Whatever you do throughout your day, you are constantly bringing microbes onto and into your body. Especially when eating, you introduce a mix of microbes into your gastrointestinal tract.

In this dark, airless place, microbes flourish, working tirelessly to keep you in good shape. They improve your body’s health starting from the gut and strengthen your gut’s defences by fighting off unwelcome intruders.

Gut bacteria break down the food you eat from which they produce all sorts of molecules. The most important ones are called short-chain fatty acids. These small molecules impact the health of your gut and your overall body.

Here, we’re looking at gut bacteria that produce short-chain fatty acids and how they maintain the health of your gut. We’ll also explore ways to help bacteria make even more of these beneficial molecules.

Let’s start by understanding how your gut protects your body.

The mucus layer of the gut as a first line of defence

The food you eat passes through your body, yet it is always in contact with your body’s outer layer of cells. Only in the gastrointestinal tract do your gut cells absorb molecules from food and transport them into the body.

This means the outer layer of your gut, the so-called epithelium, faces away from the body and is in constant contact with the outside. One of its main jobs is to prevent harmful components from getting too close or even entering the body.

That is why goblet cells, which are special gut epithelial cells, produce a thick, slimy mucus. As they constantly secrete mucus, the cells actively push everything away from the epithelium, while the ever-growing mucus layer sits like a protective shield on top of the the intestinal epithelium.

When the mucus layer is too thin or broken, harmful microbes and bacteria can come into contact with the gut. This can trigger inflammatory immune responses, resulting in chronic diseases such as inflammatory bowel diseases.

Commensal gut bacteria produce short-chain fatty acids

While this slimy physical barrier is already a strong first line of defence for your gut, you can also rely on your gut microbes. Those that reside in and on your body over a long time are called commensal microbes.

One way to make them stay with you is by feeding them their favourite foods. Gut bacteria eat what you eat, while some commensals like Ruminococcus gnavus and Akkermansia muciniphila also eat the mucus in your gut.

And from your food, the majority of gut commensals prefer the dietary fibre. That is the indigestible part of plant-based foods as it passes through your small intestine unchanged. Once it reaches the large intestine, your gut bacteria get to work.

They break down the fibre, ferment it and produce all sorts of molecules from it. The most important group of molecules are the short-chain fatty acids, including acetate, propionate and butyrate.

The commensals Bacteroides thetaiotaomicron, Bifidobacterium longum, Eubacterium and Blautia coccoides are actually some of the best-known producers of short-chain fatty acids. Just by eating a lot of dietary fibre, you increase both the different microbial strains growing in your gut and the amount of short-chain fatty acids they make.

How short-chain fatty acids improve gut health

From the gut, short-chain fatty acids diffuse through the mucus and reach the epithelial layer. Here, they bind to receptors on the goblet cells and activate certain pathways.

They trigger goblet cells to grow and produce more mucus. This increasing mucus layer, in turn, protects more effectively against harmful bacteria while providing more food for your commensals.

For example, two gut bacteria, Akkermansia muciniphila and Blautia coccoides, produce the short-chain fatty acids acetate and propionate. Both molecules trigger gut cells to make more mucus, improving gut health and feeding commensal bacteria while fighting off intruders. In mice, Bifidobacterium longum induces the growth of mucus, likely by producing acetate.

The diet-microbiome-gut health connection

Now, let’s tie all these pieces together: By eating plant-based fibres, you feed your beneficial gut bacteria. These digest and ferment the fibre and produce short-chain fatty acids, which bind to your gut cells and trigger them to produce more mucus. This increasing mucus layer shields off your gut while feeding your gut bacteria.

Generally, the more fibre we eat, the more beneficial bacteria live in our guts. They become more active at digesting fibre since they lose their appetite for the mucus.

Beneficial bacteria like Blautia can even be found in human stool after 12 weeks of eating high-fibre diets. Hence, it seems that the commensal Blautia decides to settle down in your gut depending on what you eat. So, by eating food full of fibre, you can attract helpful bacteria to you.

On the other hand, when you eat little fibre, your gut bacteria start eating your mucus layer, since their preferred substrate is not available. This can lead to inflammation and other gut health issues.

You are what you and your bacteria eat

When considering the role of your gut bacteria for your health, the saying “you are what you eat” may take on a new meaning.

By eating a lot of different plant fibres, you’re not just feeding yourself — you’re also feeding the bacteria in your gut. Your food gives them the right fuel to produce short-chain fatty acids that strengthen your gut’s protective layer and gut health. This, in turn, impacts the health of your body, mind and cardiovascular system and even your emotional and mental wellbeing.

Hence, by eating more veggies, fruits and seeds with lots of fibre, you influence which types of bacteria live close to and inside of you. So, what you eat affects how you feel, quite literally from the inside out.

Your gut bacteria will thank you for that extra serving of vegetables. To show their gratitude, they’ll provide you with all the good stuff to keep you healthy.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

The term “sustainability” was introduced. This concept focuses on a world in which we live well within the resources of our planet, today and tomorrow. Based on environmental, social and economic sustainability, the United Nations launched the 17 Sustainable Development Goals in 2015.

The idea was to combine science, society and technology to reach these goals and create a healthier planet and society. Fortunately, among the many contributors to this mission, we also have our tiny friends—microbes.

About the role of microbes in sustainability development

Microbes have existed for billions of years, making up 99% of our ecosystem. They have been breaking down waste, recycling matter and helping maintain balance on Earth long before humans arrived.

Considering that microbes and bacteria influence most of the 17 Sustainable Development Goals, scientists aim to use their superpowers for the sustainable development of our planet. So, let’s look in more detail at how microbes impact planetary sustainability:

Goal 2: Zero Hunger

Microbes are directly and indirectly involved in food production and agriculture.

• Microbes ferment food, increasing its shelf life and nutritional value. Tasty and staple foods like bread, yoghurt, cheese, sourdough, chocolate, sauerkraut, kombucha, cider, idli, beer and wine are indeed products of fermentation
• They fix nitrogen in the soil, naturally improving soil fertility and crop growth
• They help restore carbon in the soil, supporting good farming practices

Some microbes are even food themselves! Many bacteria and fungi are protein sources for both humans and animals. They are grown from agricultural and industrial waste and purified to meet food quality standards. This so-called ‘Single-cell protein‘ or microbial protein is now being explored as an eco-friendly and nutritious alternative to animal-derived protein.

Goal 3: Good Health and Well-being

While some bacteria do cause disease, many others do the exact opposite:

• Bacteria are used as factories to produce life-saving antibiotics, cholesterol-lowering and anti-cancer drugs
• Bacteria can be engineered to produce vaccines and therapeutic agents or transport drugs within the human body
• Probiotic bacteria, those that, when taken in appropriate amounts, are beneficial to human health, improve digestion, boost immunity and enhance our overall well-being

Goal 6: Clean Water and Sanitation

Yes, some bacteria can contaminate water and you surely want to keep these out of your water. Yet, other microbes do the opposite:

• They break down organic waste in water treatment plants
• They can clean up oil spills and even neutralise toxic chemicals, helping recycle water for reuse

Goal 7: Affordable and Clean Energy

One of our global challenges is to reduce our dependence on non-renewable fossil fuels for electricity and energy.

• Bacteria come to the rescue as they produce bioelectricity from organic material, the so-called cable bacteria, conducting electrons across a few centimetres
• Bacteria can convert renewable materials like agricultural and industrial by-products into clean liquid biofuels, offering eco-friendly alternatives to fossil-derived fuels

Goals 9 and 12: Industry, Innovation and Infrastructure & Responsible Production and Consumption

One way to protect our environment is to produce essential materials from renewable sources and recycle waste in industries – an approach called circular economy. Some microbes can degrade organic material, while others produce various chemicals and necessary materials. That is why microbes play a key role in this sustainability area.

• Bacteria can produce the building blocks required to make plastics from renewable materials
• Bio-based plastics are broken down more quickly than conventionally produced plastics, saving our lands and oceans from plastic pollution

Goal 13: Climate Action

Despite ongoing efforts, greenhouse gas emissions remain high due to human activity, leading to adverse climate change. It is expected that the global temperature will rise by 2.5°C by 2050.

• Microbes can capture and convert greenhouse gases like carbon dioxide into low-carbon fuels and useful value-added chemicals
• Some microbes transform carbon dioxide into organic material, which other species use

Since microbes have been maintaining the carbon balance in the ecosystem for ages, they are essential players in curbing climate change. Yet microbes are adapting and changing their behaviour according to climate change. Understanding the relationship between the production and consumption of greenhouse gases by microbes and climate change can help us restore balance sooner rather than later!

Goal 14: Life Below Water

Pollution from human activities is impacting our oceans. We see that the residuals of medicines, caffeine from the coffee we consume, harmful waste from industries, plastics and heavy metals go right into the ocean.

All of this often has a negative effect on marine ecosystems. Gladly, microbes can help break down these harmful pollutants. They use toxic substances as food and convert them into less toxic by-products, water and carbon dioxide. This is called bioremediation, a process that keeps our waters and marine ecosystems clean and healthy.

Goal 15: Life on Land

All life on land needs food. We depend directly and indirectly (through animals) on plants for our everyday nutrition. Plants get their essential nutrients from soil, with microbes having a huge impact on the amount and availability of soil nutrients.

• Microbes help in converting atmospheric nitrogen into a usable form in the soil for plants to use. They also help in making insoluble phosphorous, potassium and sulphur in soil accessible for plants to take up. In doing so, microbes act as biofertilisers as an alternative to chemical fertilisers.
• They are also key players in our food system by preventing the growth of harmful microorganisms that can cause crop diseases, becoming an alternative to chemical pesticides.

Microbes in the ecosystem work in groups to transport chemicals between the atmosphere and land, maintaining a natural balance. However, with human activity, the microbial communities are affected and disturbed. While we still don’t fully understand the extent of their role in ecosystem functioning, it is possible that supporting co-living microbial communities in the environment can help restore the ecosystem.

Goal 16: Peace, Justice and Strong Institutions

Throughout history, the growing demand for better food, resources, health and living conditions has often led human societies to compete—and sometimes even to go to war. But as we’ve seen, microbes offer solutions and services across various spheres of our needs. So microbes can even help us promote harmony and peace – one of the foundations of social sustainability.

How microbes can support achieving sustainability

We’re now beginning to understand the power of microbes in moving towards a greener planet. So next time you want to make an impact on the health of our planet, you can also include microbes in your decision-making.

You could, for example, choose products responsibly produced using bio-based processes, encouraging industries to shift to circular bioeconomy. Composting waste from your kitchen to be used as biofertiliser is a great way to use microbial superpowers on a small-scale level.

There’s still a long way to go in terms of large-scale production and applications, but progress is underway. By recognising and harnessing the potential of microbes, we can make a difference and move a step closer towards the UN Sustainable Development Goals. The future of sustainability might just depend on microbes, their superpowers and the innovative ways we choose to work with them.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Consider the scent of a ripe cheese or a glass of wine—these aromas come from bacteria and other microbes. Even less pleasant odours, like old sweat, smelly feet or a mouldy apple, are thanks to molecules produced by microbes.

Let’s explore the fascinating world of bacterial smells, their origins and what we can learn from them.

Microbial smells come from volatile organic compounds

All microbes produce volatile organic compounds as part of their metabolism. These molecules are generally gaseous and vaporous, allowing us, animals and even plants to smell and react to them.

Depending on their environment, the substrate they use, pH, salt concentration and temperature, microbes produce various volatile organic compounds. These can range from simple gases like carbon dioxide or ammonia to organic acids such as isovaleric acid or large and complex steroid derivatives.

For both microbes and us, volatile organic compounds serve as a means of communication and information. As we’ll see, these small compounds play crucial roles in microbial communities and their survival. On the other hand, for us, certain volatile organic compounds signal to our brains that bacteria are present, indicating that something may not be safe to eat or drink.

Some bacterial odorous molecules have a dual nature: indole, produced by gut bacteria from food, gives faeces its characteristic odour. Yet, at low concentrations, indole has a flowery scent and is even used in perfumes.

Bacteria attract animals with earthy smells

Do you recall the scent of fresh rain? That earthy, musty smell comes from a molecule called geosmin, produced by bacteria of the Streptomyces family.

Streptomyces live in the soil, where they produce soil material and form long thread-like filaments. To survive and spread, they use the volatile organic compound geosmin.

When these bacteria release their spores into the soil, they cover them with both antibiotics and geosmin. While the antibiotics protect the spores from other microbes, geosmin attracts small insect-like animals. These creatures eat the spores and distribute them in the environment.

In this case, geosmin signals a food source to the animals as the spores nourish the animals. At the same time, the spores use the animals for transport to new areas. Once conditions improve, the spores develop into bacteria and start forming their filaments in the soil.

Also mosquitoes are attracted to the smell of geosmin in ponds and waters. Here, cyanobacteria produce the molecule, so the mosquitoes decide to lay their eggs here as the bacteria are food sources for the larvae.

Bacteria produce characteristic food smells

Other pleasant and unique bacterial smells come from the fermentation of fruit, vegetables or milk. During this process, bacteria produce compounds that give food not only their characteristic tastes but also aromas.

As an ancient fermentation product, vinegar has a very characteristic sour smell due to volatile organic compounds produced by microbes. Mainly bacteria from the Lactobacillus and Leuconostoc families and some yeasts degrade the sugars of cereals or fruits to produce acids and alcohols.

Also, the fine aromas of wine and cheese come from the many volatile organic compounds bacteria and yeasts produce during fermentation. They include alcohols, aldehydes, ketones, lactones, esters as well as many other classes of chemicals. As you probably know, depending on the origin of the grapes or milk, the ripening temperature and the microbes added, the resulting product can taste and smell entirely different.

However, the unpleasant smell of rotten foods is also due to bacterial metabolic activity. Meat, fish and eggs contain molecules like choline and trimethylamine oxide. Over time, bacteria break these down into trimethylamine. Your brain likely recognises this off-flavour as a sign of food decay, triggering you to reject rotten foods to protect your health.

Bacteria create your unique body odour

Interestingly, your body odour changes based on what you eat and which microbes and bacteria you introduce into and onto your body. Depending on your diet and health, your body secretes different mixes of sweat—generally a watery mixture of minerals, amino acids, fats, urea and antimicrobial substances.

Although your skin produces odourless sweat all over the body, some areas are more hospitable for bacteria and microbes than others. Consider your armpits, where your main body odour originates: They contain more sweat glands and slightly different hair follicles, making them moister and more enclosed. With more water and nutrients available, your armpits are very microbe-friendly.

Consequently, the microbial communities in your armpits can differ completely from the rest of your body. Here, three bacteria—Corynebacterium striatum, Corynebacterium jeikeium and Staphylococcus haemolyticus—have special strategies to survive the high salt content of sweat and even use the urea in sweat as food.

They break down the molecules in sweat into volatile organic compounds that together give each person their unique body odour. For example, sulphur-containing compounds, often with strong onion-like smells, are produced by Corynebacteria.

Our sweat also contains lactic acid and glycerol, from which Staphylococcus and Propionibacteria produce acetic and propionic acid. These molecules directly impact your body odour as they evaporate leaving a pungent smell or supporting the growth of other bacteria. But our smelly sweat has advantages too: After eating citrus fruits, people’s sweat contains limonene, a mosquito-repellent possibly generated by skin bacteria.

Bacteria are responsible for smelly feet

Another significant area of your body directly impacted by bacteria and their smell-creating superpowers is your feet.

Our feet actually contain the highest variety of microbial communities, with Staphylococcus, Corynebacterium and Brevibacterium being the most common. These bacteria feed on skin particles, urea and the amino acids in sweat.

For example, Staphylococcus epidermidis, a normal resident of human skin, degrades the amino acid leucine into isovaleric acid. Unfortunately, this molecule has a powerful, rancid cheese-like odour—the reason for smelly feet.

Fortunately, other bacteria, like Brevibacterium, Micrococcus and Kytococcus, can completely degrade both leucine and isovaleric acid, thus preventing the unpleasant smell. As usual, it comes down to having the friendly bacteria around.

Bacterial smells in your life

As we’ve seen, the world of bacterial smells is fascinating and complex. From the earthy smell of rain to the rancid odour of sweaty feet, bacteria play crucial roles in creating the smells that surround us.

These microbial odours are not just curiosities; they have important functions in nature and human biology. They can act as communication signals between microbes, influence animal behaviour, make our food smell delicious and even impact our unique body odour. So, embrace the microbial world with all its facets, colours and smells!

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

The complement system is the first line of immunity defence

As part of the innate immunity, the so-called complement system consists of several proteins. These get activated sequentially and function together to finally destroy any pathogen.

To recognise harmful bacteria, complement proteins have special receptors. These bind to specific proteins on the surface of the bacteria, so-called pathogen-associated molecular patterns, or PAMPs for short.

Imagine the bacterial PAMP as a key that perfectly fits into the groove of an immune receptor lock. The binding between these two proteins activates the immune system and triggers mechanisms that aim to clear out the pathogen.

The enzymatic lock & key hypothesis.

The immune system recognising different bacteria

Bacteria come in two main types: Gram-positive and Gram-negative bacteria. Depending on which type a bacterium is, it has different PAMPs. Luckily, your immune system has evolved to identify both of these structures.

Gram-positive bacteria are surrounded by a rigid layer, the so-called peptidoglycan cell wall. Within this layer of carbohydrates and proteins are the modified carbohydrates teichoic acid and lipoteichoic acid. These are the PAMPs, that your immune system recognises and binds to.

The Gram-positive bacterial cell surface. Created with BioRender.com.

On the other hand, Gram-negative bacteria contain an additional capsule layer on top of the peptidoglycan wall. This layer is made up of another type of carbohydrate, the lipopolysaccharide, which is the PAMP of Gram-negative bacteria. So, even though Gram-negative bacteria also contain a peptidoglycan cell wall, it is covered by the capsule and thus inaccessible to the immune system.

The Gram-negative bacterial cell surface. Created with BioRender.com.

How does the complement system work

Imagine a harmful bacterium managed to sneak into your body. To prevent any intruder from causing damage, the sensor proteins of the complement system are constantly patrolling the bloodstream, hunting for malicious beings that aim to harm the body.

As soon as a sensor protein recognises and binds to a bacterial PAMP with its lock, it alerts the complement system. The sensor protein begins to produce a key enzyme called C3 convertase.

A complement sensor protein binds to a bacterial PAMP. Created with BioRender.com.

Within your blood, there are lots of small complements called C3. And the main function of the C3 convertase is to break down this C3 into small C3a and large C3b fragments. This is the most important step in complement activation and from here everything else happens.

C3 convertase production and its subsequent action. Created with BioRender.com.

Now, the bloodstream is flooded with C3b fragments which bind to the bacterium’s surface. As more C3 proteins are broken down, more C3b large fragments are produced and more bind and coat the bacterium. This process is called opsonisation.

Illustration of opsonisation by C3b. Created with BioRender.com.

The immune system gets rid of bacterial intruders

The C3b-covered bacterium now acts as a location device for phagocytes. These arrive and bind to the C3b fragment very tightly. This keeps the bacterium locked and prevents it from moving around.

Now begins the process of phagocytosis, whereby arm-like structures extend around the bacterium, eventually engulfing, ingesting and destroying it. The infection is finally cleared.

Phagocytosis of a bacterial pathogen.

In some cases, however, phagocytes do not arrive fast enough to the site where the C3b-covered bacterium hangs around. In this case, other complement proteins, such as C5 and C6, begin to spontaneously assemble around C3b and form the so-called membrane attack complex (Figure 6). This complex punctures a hole into the cell surface, which looks like a gunshot wound, causing the bacterium’s innards to spill out and dissolve.

Formation of the membrane attack complex via the self-assembly of complements. Created with BioRender.com.

How does the complement system differentiate between commensal and pathogenic bacteria?

You are probably aware that in your body also live many friendly bacteria, the so-called commensal ones. And you do not want to get rid of these helpful bacteria. Hence, the immune and complement systems have adapted several strategies to keep your friendly bacteria and focus their killing power on harmful intruders.

For example, commensal bacteria reside only in certain areas of your body like the gastrointestinal tract. They do not float around in the blood. Your immune system is aware of this. Hence, the complement system in the gastrointestinal tract is modified and does not attack these commensal bacteria. Instead, their recognition skills focus on harmful intruders.

Also, commensal bacteria contain additional molecules on their surfaces to hide their PAMPs from the complement system. This prevents the complement system from getting activated.

The complement system as the first immune fighters

As you’ve seen, the complement system works tirelessly, day and night, patrolling your bloodstream to ensure that no harmful bacterium gets too comfortable inside. With its sensor proteins, it identifies these pathogens and activates the immune army to clear out any infection.

Hence, the complement system is the crucial first line of defence of our immune system. By recognizing and targeting harmful bacteria and sparing beneficial commensal bacteria, it ensures that your body remains healthy and free from infection.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Whatever it was, chances are high that part of your food was fermented by microbes. As exceptionally healthy and tasty as fermented foods are, these would not exist if it weren’t for microbes and their fermentation superpowers.

Yet, microbial fermentation is a lot more than processing food and giving it a new taste or aroma. Indeed, depending on who you ask, microbial fermentation means slightly different concepts.

For once, fermentation is a metabolic pathway in some microbes and organisms. It is an energy-saving way to degrade and metabolise substrates and produce complex and energy-rich fermentation products.

Secondly, microbial fermentation describes the process of preserving food based on the fermentation pathway. For this, we let microbes break apart and ferment food in a controlled manner, eventually producing well-known fermented foods, like yoghurt, beer and chocolate.

Lastly, the industrial process of growing microbes in big cultures is often called microbial fermentation. The goal of this process is for microbes to produce a specific product – and often they do so through the fermentation pathway.

As you can see, the different definitions for microbial fermentation are grounded on the same principle: microbes degrading substrates and making fermentation products from them. Here, we will look closer at the biochemistry of microbial fermentation and explore some examples of where this microbial superpower naturally occurs and how we make use of it.

The biochemistry of microbial fermentation

From the view of a biochemist, fermentation is first of all a metabolic pathway to conserve energy. Most organisms gain energy from opening chemical bonds of molecules. This releases the energy-rich electrons that are bound within the bond. They then save these electrons in other molecules or fuel cellular machineries.

Most microbes have one preferred substrate for their metabolism. For many, this is glucose, the same sugar that our cells preferably burn and degrade. By degrading glucose, they (and us) produce several intermediary products, the most important one being pyruvate. This degradation process sets free several electrons, which microbes save in a molecule called ATP. ATP is the main fuel for microbial growth machines, swimming motors or transporters.

Sometimes microbes find themselves in environments with an excess of their preferred substrate. In this case, setting free all the energy would produce a lot of heat, damaging or even burning the cell. Hence, as an alternative, energy-conserving pathway, they switch to fermentation metabolism.

During this pathway, they degrade the substrate only partly, thus not extracting all available electrons from it. Instead, they use one of the intermediary products and bind it to another molecule in an energy-neutral reaction. This conserves the electrons and energy within the fermentation product.

What makes fermentation so fascinating: Many species have unique fermentation pathways. Depending on their genes, they branch off the fermentation pathway at any intermediate and produce different molecules.

For example, from pyruvate, some microbes produce ethanol, which we use for beer or wine production, and others produce lactic acid, like for yoghurt production. Other microbes ferment substrates like citrate or succinate and produce complex molecules like caffeine or colourful biopigments.

By conserving the high-energy electrons in the fermentation products, microbes produce fewer ATP molecules. Hence, they have less energy available at that moment. But if they need energy later, they can break down the fermentation product to extract the electrons. Often though, their energy levels are so high, that they even export the product to get rid of it.

Fermentation is thus a way for microbes to process molecules and conserve energy. Gladly, we learned to make use of this pathway as microbes help us convert energy-rich substrates into beneficial products.

Microbial fermentation for food preservation

One source of energy-rich substrates are carbohydrate and fibre-rich foods, which is why these are some preferred environments for microbes. By fermenting fruits, vegetables, milk and grains, microbes can grow and spread on seemingly any plant-based substrate.

Gladly, we learned to grow microbes and ferment food in controlled environments, making food fermentation one of the oldest human technologies. Throughout history, many cultures have optimised different fermentation processes and created all kinds of products.

Food fermentation can include adding so-called starter microbes to the food or using those microbes that naturally live in the foodstuff. These microbes break apart the carbohydrate component of the foodstuff to fuel their fermentation pathways.

The resulting fermentation products can be beneficial vitamins, antioxidants or molecules that change the aroma, taste, texture or stability of the foodstuff. The degradation and modification of the food itself and the accumulation of fermentation products, over time, make our well-loved cheeses, coffee, bread, chocolate, beer, wine, kombucha, yoghurt or kimchi.

For example, thanks to microbes, cheese and yoghurt taste and smell differently than the original milk. Coffee and chocolate get their complex and unique aromas only thanks to the microbial fermentation of coffee and cocoa beans.

During fermentation, many bacteria produce strong acids from the original substrate. Thus, the resulting food becomes acidic and sour, which prevents other microbes from growing and spoiling the food. That’s why food fermentation became an efficient way to conserve food. Many vegetables, like cabbages, pickles or olives, are thus preserved into sauerkraut or kimchi, sour pickles and olives, and the like. Also making kombucha, kefir or cheese are ways to preserve the original tea or milk.

When fermenting cereals, yeasts mainly produce carbon dioxide or ethanol. Carbon dioxide, for example, in sourdough bread makes the bread rise. In the beer-brewing and wine-making processes, yeast produces ethanol as well as several beneficial and aromatic molecules that give beers and wines their tasteful and diverse aromas.

About the microbes involved in food processing

Each fermented food has a unique community of microbes that changes with the fermentation process over time. With the rise of one microbial species, the pH of the food might change or a certain substrate becomes available, which might kill one species or feed and thus help another one grow.

In many vegetable-based fermentation products, lactic acid bacteria, such as Leuconostoc, Lactobacillus and Weissella, are the primary microbes. They produce acids which prevent food-spoiling microbes from growing. The acids also give the resulting kimchi and sauerkraut their sour and acidic tastes. On the contrary, in alkaline-fermented foods of Asia and Africa and in bean-fermented foods, such as tempeh, miso or natto, Bacillus bacteria are usually responsible for the fermentation process.

In milk fermentation, bacterial cultures are of two types: Lactococcus, Lactobacillus, Leuconostoc and Streptococcus bacteria that acidify the milk. This denatures the milk and produces yoghurt-type products, such as yoghurt, buttermilk and kefir.

As a second step during the cheese-making process, Brevibacterium, Propionibacterium, Debaryomyces, Geotrichum and Penicillium are added. These bacteria and fungi produce more complex molecules and give the ripening cheese its unique flavour, texture and aroma.

For cereal fermentation, yeasts are the most widely used microorganisms, producing beer, sourdough bread, sake and whiskey. For bread-making, the principal yeast is Saccharomyces cerevisiae. Other Saccharomyces species, as well as Torulaspora, Hanseniaspora and Pichia are responsible for fermenting most cereal-based drinks.

How the human body benefits from fermentation

As we’ve learned above, many fermented foods are full of microbes – as long as the food was not heated or pasteurized. Hence, when eating fermented foods, you also take in the microbes in and on the food. And these are ready to settle in your body, feed off your food and do some more fermentation.

After arriving in your gastrointestinal tract, the microbes start digesting part of your food too. They degrade the plant cell structures of vegetables, fruits, cereals, seeds and nuts as well as non-digestible fibres. This releases sugars which gut microbes ferment to short-chain fatty acids and gases, like methane. These fermentation products have beneficial effects on your digestion, mental and gut health as well as your immune system.

Hence, by eating fermented foods you gain beneficial microbes – some of them are the so-called probiotics. And by eating plant-based foods you give your gut microbes the appropriate food to ferment, which is what makes some of them prebiotics.

But this is not the only place where microbial fermentation takes place in your body. For example, Lactobacillus bacteria are the key players within the vaginal microbiome and their fermentation activities influence the health of women.

Within the vaginal tract, host cells provide Lactobacillus with glycogen. From this, the bacterium sets free glucose and ferments it to produce lactic acid and hydrogen peroxide. These molecules decrease the pH creating an acidic environment within the vagina. This acidity kills some pathogenic microorganisms directly and prevents others from growing. Hence, by feeding residential Lactobacillus bacteria, the body helps them grow and in return they protect it.

Microbial fermentation as a pillar of industrial production

The more we learn about microbes, bacteria and their fermentation pathways, the better we can use their metabolic superpowers for our own good. Especially the biotechnology and food industry are making great use of microbial fermentation.

We now grow microbes in big batches and harvest fermentation products, like bioethanol, lactic acid or vitamin B12. In many cases, microbes grow on plant-based products or even ferment waste into usable and, thus, green products. As you can guess, food fermentation based on appropriate starter cultures is taking place on large scales to produce many of our beloved foods.

As such, microbial fermentation is an essential part of our lives. Not only as a fundamental process in cellular metabolism and thus human health, microbial fermentation has become a key pillar in food production and preservation as well as industrial production.

As a sustainable tool to produce plant-based foodstuffs, pharmaceuticals and fuels, microbial fermentation may even play a crucial role in our journey towards a greener and more resilient future. Just another reason to be grateful to microbes and their fascinating superpowers.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Below are a few ways how bacterial research is and continues to make advancements in modern science.

Treatment Courses

Microbiologists working in diagnostic laboratories perform tests on samples which come from either humans or animals.  Doctors or veterinarians analyse these samples to detect the susceptibility or resistance of bacteria to antimicrobial drugs. This kind of research is incredibly important when it comes to discussing the right courses of treatment and future preventative measures that can be taken.

Similarly, biochemists and microbiologists analyse body fluids to identify if and which disease-causing organisms are present. With this bacterial research, doctors can adequately diagnose patients to ensure that they get the right treatment plan in the shortest time possible. Also, the research done by biochemists helps nurses and doctors alike to understand what will and won’t work for certain patients.

Food Health

With microbiological techniques, food preservation is possible. Thanks to modern science and continual research, microbiologists can identify pathogens in food products. These pathogens, if left alone, can end up spoiling the goods and make us sick.

By examining multiple food samples, researchers can determine if contaminants are present and what kind they are. For instance, the type of bacteria that may be found. The results of such examinations help scientists assess the products that are dangerous to human health and those that are not.

Manufacturing Foods

Microbial fermentation helps break down larger food components into simple ones. It is one of the most natural ways for improving vitamin, protein and anti-nutrient content as well as enhancing the flavour and appearance of food.

Fermentation processes are based on microbes like yeast and bacteria that change the food matrix of fruits, vegetables or beverages. Fermented foods include sourdough bread, beers, wine, yoghurt, sauerkraut, kimchi and even cheese.

Medicine

Studying how the human immune system works is incredibly important. To shed light on this question, microbiologists and immunologists work closely together to unravel how pathogens overcome the immune shield of the body. Based on this knowledge, they can then aim to find strategies to fend pathogens off.

Microbiologists are further investigating how “good microbes” help our body function. By better understanding how the human microbiota works and supports us, researchers are aiming to find new strategies to use the microbiota to keep us healthy and fit.

Since the human microbiota also impacts disease and treatment progresses, researchers are currently looking into ways to support the microbiota. This would eventually improve treatments and support the health of people.

The Future of Microbiology

There’s something positive on the horizon regarding the future of microbiology. All of the scientific shifts have brought about new opportunities in different areas of study: food manufacturing, fermentation, medicine and treatment. Such developments will only be beneficial to human life and the environment around us.

Proper, up-to-date Microbiology Laboratory Equipment is an essential part of any microbiology lab no matter the type of research. Advancements in the technology used by microbiologists help accelerate their research and progress in discovering new pathogens and treatments.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Those bacteria that call your gut their home are the so-called commensal bacteria. Luckily, they have a special superpower: They can protect us from bacteria that cause infections and make us sick. For this, our commensal gut bacteria developed some extraordinary strategies to defend these pathogens.

So, by nurturing our friendly gut bacteria, you are also strengthening your protection against diseases. Here, we will look at what kind of bacterial wars are going on in your gut and how your gut bacteria defend pathogens and keep you healthy.

Your gut bacteria defend pathogens with toxic molecules

Bacteria have many different means to kill other microbes, competitors or even their own siblings. Often, these bacteria produce molecules that are toxic to their prey, which means they inhibit cellular proteins or machineries. Without these machineries, the prey is then lacking an essential cell function to grow or survive, so that it eventually dies.

Interestingly, gut bacteria produce and deliver many different toxic molecules of various shapes and sizes, functions and even origins.

Gut bacteria produce bacteriocins

Many bacteria produce molecules that are like antibiotics specifically to kill bacteria. These are called bacteriocins.

Some bacteriocins are simple and small molecules, while others can be big and fancy. However, they all have a similar goal: they bind to a specific target in the prey bacterium and prevent that target from working properly.

So, no wonder that many bacteria in our gut microbiome produce bacteriocins that are toxic to pathogenic intruders. Also, we carry a lot of different bacteria in our guts and they all produce different bacteriocins. Hence, incoming pathogens face this huge load of toxic molecules making it really difficult to establish themselves in our intestines.

For example, one bacterium that loves the warmth and lack of oxygen in our gut is the bacterium Ruminococcus gnavus. And this one produces at least two bacteriocins, Ruminococcin A and C, that are toxic against human gut pathogens like Clostridium perfringens.

Other friendly gut bacteria, like Escherichia coli or Blautia producta, also produce bacteriocins that are toxic to pathogens, like Enterococcus faecalis. And some of their bacteriocins can even impact our gut cells by activating and strengthening our immune response.

Gut bacteria produce short chain fatty acids from fibres

Another way to protect against pathogenic gut bacteria is directly related to your diet. When we eat a lot of fibres, which are non-digestible carbohydrates, our friendly gut bacteria break these up. From these fibres, they produce small molecules that are called short-chain fatty acids, which have many positive health benefits for our overall wellbeing.

Interestingly, when we have a lot of these short-chain fatty acids in our intestine, the pH drops. This is already pretty difficult for most pathogenic bacteria, as not many can handle this acidic environment.

Plus, short-chain fatty acids diffuse into pathogenic gut bacteria where the pH drops as well. This can disturb many cellular machineries from functioning properly and not many bacteria have the right tools to defend against this attack, so they’ll die.

Gut bacteria convert bile acids into toxic compounds

To better digest the fats in food, our liver produces bile acids. These molecules bind fatty acids and lipids so that we can take them up better into our bodies.

But some of our friendly gut bacteria can convert these primary bile acids from our liver. For example, one of these bacteria, Clostridium scindens, transforms them into secondary bile acids that can bind the lipids of bacterial membranes.

Like this, secondary bile acids open the membranes of some pathogenic gut bacteria, like Staphylococcus aureus, Bacteroides thetaiotaomicron or Clostridoides difficile. This eventually kills the intruders and keeps our guts pathogen-free.

Killing pathogens with bow and arrow

Yes, also direct bacterial wars are happening in our guts! And they are nasty!

Some bacteria use tiny little bows to shoot deadly arrows into other bacteria. And these arrows can be incredibly toxic so the shot bacterium has barely any chance to survive the attack.

Luckily, our gut bacteria use their bows and arrows to defend against gut pathogens. For example, commensal bacterium Bacteroides fragilis has three different bows and can shoot various arrows. And research showed that this bacterial friend can protect us from bacteria that otherwise cause intestinal diseases.

Interestingly, Bacteroides fragilis is not opposed to hit’n’kill its own toxic bacterial siblings since some members of his family can indeed make us sick. But our friendly Bacteroides fragilis collected many different immunity proteins against its evil siblings so that their toxic arrows cannot harm it. Instead, Bacteroides fragilis keeps shooting and killing until we are safe from the pathogenic sibling.

Keeping nutrients from pathogenic gut bacteria

Another important way how gut bacteria defend pathogens is by keeping nutrients away from them. In all mixed microbial communities, bacteria fight for nutrients, especially for metals like iron, zinc but also sulphur sources.

Luckily, our gut bacteria developed some sneaky ways to steal these metals from gut pathogenic bacteria. By sending out special proteins that bind these metals very tightly, the commensals make sure to keep these metals from the pathogens. And if the pathogenic bacteria don’t have enough of these essential metals, they won’t survive and will eventually die.

Strengthening the mucus layer to block pathogenic gut bacteria

When you think about it, your gut is not part of your body – even though it is inside of you. All the food that we eat, stays within this digestion tube (mouth, oesophagus, stomach, intestines) until it comes out on the other side.

And to protect us from harmful microbes and molecules, we need to have a clear physical barrier from the content of the tube. This barrier is the so-called epithelial layer, which is covered by a slimy mucus on the outside. And this sticky slime helps keep off intruding microbes so that they cannot breach through the epithelial wall and get into our bodies.

Luckily, our helpful gut bacteria help us maintain this slimy defence wall. As bacteria produce SCFAs close to the mucus layer, the epithelial wall produces more slime. And if the slime gets thicker, gut pathogenic bacteria have more difficulties getting into our bodies.

To help the slime grow, some bacteria adapted very well to the conditions within the gut. For example, the friendly gut bacteria Akkermansia muciniphila and Ruminococcus gnavus cut off the very end of the mucus layer and feed themselves with them. This does not harm the mucus itself, but it keeps these bacteria close by. And this in turn triggers the epithelial wall to produce more mucus. So, everyone wins.

How to help your gut bacteria defend pathogens

Now, that you better understand how your gut microbiome defends pathogenic gut bacteria, make sure you support them keeping you healthy. By feeding your gut bacteria the right foods, you will help them be comfortable and happy in your gut. And when the right bacteria grow within you, they will gratefully protect you from nasty intruders!

Another idea for researchers is to use what they have learned to keep you healthy. The idea is to develop probiotics or prebiotics that help us defend against nasty pathogens. For example, you might take pills containing toxins against pathogenic gut bacteria or probiotics with bacteria that can fight off pathogens.

Whatever it may be, you can always help your gut bacteria be happy in your intestines by eating the right things. That means lots of fibre and veggies! ?

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

I am fascinated by the impact that these tiny organisms have on our bodies and health, the environment, climate and even food. And I am always amazed by how everything is interconnected; how microbes in the soil can shape the weather and the climate and how microbes in our guts from the food we eat shape both our mental and physical health. Mind-blowing!

With such a huge impact on our lives, microbes even shaped human history, politics, culture and advancement. Due to their integral influence on everything we do, I am convinced that we should all learn more about the fascinating microbes and bacteria all around us.

Sure, this is the main motivation that we write this blog, but there are also great books about microbes that are both educating and entertaining. Here, I want to share my favourite books about microbes and bacteria, written not only to inform but also to make you giggle about what microbes do. I recommend reading any of these microbial books if you’re slightly interested in the microcosmic world or are looking for a present for someone who is.

Disclaimer: some of these links are affiliates and I might make a small profit from your final purchase with no extra costs to you.

I Contain Multitudes: The Microbes Within Us and a Grander View of Life by Ed Yong

This book is already a classic in the microbiology literature. In an easy and funny way, Ed tells the reader how microbes affect our daily lives. After a quick introduction into evolution, Ed talks about how microbes impact our bodies, metabolism or defend us from diseases.

Ed further tells us in a light way that you should not consider your body just as it is, but rather as this multi-organism interacting, communicating and exchanging with the microbes in and on it. After reading this book, you might not see your body the same way as before.

This book about the microbial life is great for:

Everyone who wants to read light stories about microbial life and get a first overview of how microbes have always impacted us and keep impacting everything we do.

Deadly Companions: How Microbes Shaped our History by Dorothy H. Crawford

I started reading this book when the Covid19-pandemic started and felt reassured and scared at the same time. In this book, Dorothy talks about several global pandemics in human history, how these shaped our culture and politics and what we could learn from each one of them.

This book makes it clear that by advancing our communities and cultures, we gave microbes the opportunities to spread amongst us. Like this, infectious disease pandemics have always been part of our history and should be no surprise to anybody.

This book about microbial history is great for:

Everyone who is interested in human history and wants to learn more about how microbes have always impacted human life, especially our politics and culture.

Coloured Bacteria from A to Z from BacterialWorld

We, Noémie and Sarah, wrote and illustrated this book to introduce you to 26 different bacteria, one for each letter. You will get to know bacteria from different environments, their colours, superpowers and how they impact your daily life. In the descriptions for each bacterium, the reader will gain a basic understanding of bacterial cells and growth, microbial fermentation and food production, microbes’ impact on sustainability, antibiotics and health.

With hand-drawn illustrations and a final quiz section, both young children and adults can engage in a relaxing activity while learning about the colourful bacterial world. You can choose among different languages and get the book from Amazon or print the sheets yourself as often as you want.

This microbiology colouring book is great for:

Anyone who has a young child and wants them to learn while colouring. We also found lots of adults who enjoy the meditative activity of colouring and for whom this microbiology colouring book might be a thoughtful present.

Joyful Microbiology Activities Ebook by Justine Dees

Even though microbes are all around us, it is often difficult for students to grasp their omnipresence. The Joyful Microbiology Activities book brings microbiology to your home and shows you with well-explained and hands-on experiments where you can find microbes and bacteria.

A bucket list of the different locations to check out and look for microbes as well as a colourful photo atlas with images of lichens, molds and fungi helps students and curious kids get interested in the world of microbes. Justine also prepared follow-up questions and more ideas for projects and exercises, so parents and teachers can take their microbiology activities one step further.

This book about microbiology activities is great for:

Teachers with science classes as these activities are suitable for class experiments and students of multiple ages. Parents who want to awaken microbiology curiosity in their kids.

The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices, and Our Overall Health by Emeran Mayer

Emeran wrote this book for people who are interested in the little details of how microbes impact our bodies. He talks about the molecular communication between gut microbes and the rest of our body and tells the reader what they can do to positively influence this interaction.

From this book, you will also learn what that gut feeling actually is and why sometimes things just feel right or why you have butterflies in your belly when you’re excited or meet a new love. Emeran also explains why a plant-based diet is the right food for your gut microbes and which food additives you should avoid to stay strong, happy and healthy.

This book about gut bacteria is great for:

Everyone who wants to dig deeper into how microbes impact our health, mood and behaviour and wants to learn in detail about how the human body and brain work.

Invisible Friends: How Microbes Shape our Lives and the World around us by Jake Robinson

This book surprised me a little about its content. Expecting another book introducing the world of microbes, this book instead talks from a social science perspective about how microbes touch our lives. I still haven’t understood the storyline and the key message of the book, but hope it will reveal itself as I get to finishing the book.

Books about microbes and what to learn from them

Here you have six books about how microbes shape your health, the environment and even human history. These are written in languages as jargon-free as possible. And when the authors use technical words, they explain exactly what they mean.

Like this, your background doesn’t matter. As long as you’re interested in the microbial world, you will easily follow these books.

Do you have a favourite book about bacteria or microbes? Make sure to share them in the comments below, so that others can learn more about the fascinating microbial world as well!

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

You touch your face when it itches. You touch surfaces in a house. Even when you lay down in bed, you touch your phone or the bed itself.

Remember that this is a microbial world, and microbes are everywhere: on us, in us, and around us. People and their skins interact with microbes. And microbes interact with us via our skin.

About the bacteria on your skin

The skin is the largest human organ. It acts as a barrier against intruding bacteria and pathogens.

With more discoveries in the field of the human microbiome, scientists figured out that our skin also has its own microbiome. The hand microbiome is particularly interesting for public health research since we often transmit diseases via our hands.

Plus, your index finger is your most used finger. Hence, it has the greatest variety of microorganisms.

So, if you think about it; hands are never REALLY clean and people touch A LOT of things all the time.

The day to day life of your hand microbiome

During the day, we and our hands interact with a lot of different environments. All these interactions impact our hand microbiome. This means that hands do not harbor a constant, unchanging microbial community; on the contrary, it changes pretty rapidly.

Therefore, scientists cannot specify or define what is a “healthy hand microbiome”. But, what we know is that the hand microbiome of every individual can have “good” (beneficial) and “bad” (pathogens) bacteria.

“Good” or “beneficial” bacteria are the ones that live in symbiosis with humans. This symbiotic relationship is known as mutualism. This means that both humans and bacteria benefit from interacting with each other. Bacteria protect against pathogens and support the host’s immune system. Humans provide the environment – the skin – and nutrients to help microorganisms grow.

“Bad” or “pathogenic” bacteria, on the other hand, come from the environment. They can cause diseases like acne because they know how to trick our immune system. That’s why we are taught to wash our hands to get rid of these types of bacteria and avoid getting sick.

When scientists looked at what the average hand microbiome could look like, they found that bacteria are the most common microorganism. Additionally, viruses and fungi are less common in the skin microbiome of our hands. They make up less than 5% of the found microorganisms.

Factors influencing the skin microbiome of our hands

As we saw above, many factors influence what our hand microbiome looks like. And it turns out that your lifestyle has the greatest impact on your hand microbiome.

Just think about your diet, where and how you do exercises, or even about your job… All these factors impact which microbes settle down on your hands and become part of your skin microbiome.

And would you have thought that gender also influences the microbial community on your skin? Yes, it is proven that, overall, men and women have different bacterial profiles on their skin. No one knows why such a difference exists. It could be one of those things that distinguish men and women on a biological level.

Also, let’s not forget about external circumstances affecting your hand microbiome. Every time you step outside of your house, your skin microbiome changes.

Scientists also found that members living in the same household have similar hand microbiomes. So, even though every individual has their own unique collection of microorganisms on their hands, living in the same space makes them more similar to one another.

Additionally, if you own a dog, your hand microbiome and microbial community on your pet’s paws become more similar to one another. By interacting with your pet throughout the day, the microbes on your hands can exchange with those on your pet. Who knew that pet ownership can increase the diversity of bacteria on your hands?

Many different microorganisms live on our personal belongings, like cell phones and keyboards. These microbes likely come from our skin microbiome because those objects are, by far, the most touched throughout the day. Some scientists even think of introducing microbiome analyses of personal objects as an alternative to human DNA forensic investigations.

How can studying the skin microbiome help us?

Hands are like busy intersections, connecting our microbiome with the microbiomes of other people, places and things. Even a slight interaction with an inanimate object in your house can change what your hand microbiome looks like.

So, what can we learn from studying the hand microbiome? Our hand microbiome is like a second fingerprint. Hence, experiments in this field can uncover information on how to use a hand microbiome as a diagnostic tool.

Such a microbial tool would speed up the diagnosis process! By building general microbial profiles of every patient, doctors would be able to target only those areas that need immediate attention. And this would mean fewer prescriptions of broad-spectrum medications!

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

So, yes, also bacteria are always trying to find their siblings and communicate with them. And once they know they are not alone, they start reacting as a group.

Some bacteria start building biofilms – houses to keep the bacteria inside safe. Others like to talk to each other and produce goodies that everyone can enjoy. And other bacteria even form multicellular organisms with new superpowers.

Yet, some bacterial species like to move only in groups. Researchers call this bacterial movement twitching.

Bacteria can only twitch and move in groups when they have so-called twitching pili. Not all bacteria have these types of pili and – unfortunately for us – many bacterial pathogens produce them. And these bacteria use their pili to infect us and make us sick.

So, let’s have a look at what these bacterial pili are.

What are bacterial pili?

Bacterial pili look like little hair that grow out of bacterial cells.

This hair is anchored to the bacterial cell envelope and can be attached to any site of the bacterial surface. Some bacteria only have on pilus, others have two pili at opposite ends and some bacteria even produce bundles of pili that work together.

The pilus hair is a helix of an endless number of the same protein: the so-called pilin protein. This pilin works like a perfect puzzle piece: Each end of the pilin fits the next pilin piece. Like this, endless pilin puzzle pieces attach to each other in a circular manner and form a stable hair-like helix structure.

But not to lose their precious hair, bacteria need to attach the pilus to their cell envelope. For this, bacteria have a huge anchoring complex on the inside of their cell envelope. And this anchor holds the pilus at the correct location.

To make this pilus dynamic, bacteria link the anchor to a tiny motor. This motor has a ring shape that surrounds the anchor and thus the hair. And bacteria need this motor for the actual moving process.

How do bacteria move with pili?

This circular motor on the inside of the cell envelope has two main functions: to extend and retract the pilus. Endless circles of extending the pilus, attaching to a surface and retracting the pilus allow bacteria to move.

To extend or lengthen the pilus hair, the motor (orange) binds the pilin proteins inside the bacterium (grey circles) and transports them outside of the cell. This costs energy, which is why bacteria need this little motor. Hence, by adding more pilin protein to the pilus from the inside, the pilus hair (grey) extends towards the outside.

On the outside at the end of the pilus hair sits a protein (green) that can stick to surfaces. When this protein attaches to a surface, the motor on the inside of the bacterium changes its direction. Instead of adding pilins to the pilus and lengthening the hair, the motor takes pilins off the pilus and thus shortens the hair.

Now, the bacterium is attached to a surface while the pilus shortens. Like this, the bacterium pulls itself towards that surface.

This means that the attachment to the surface has to be so strong, that it can pull the bacterial cell towards this new location. This works like the bacterial superglue that some bacteria use to grow and survive.

What is the function of bacterial pili?

Bacterial pili can attach to all sorts of surfaces. Mainly, bacteria use this movement in environments of low water or on wet surfaces like human tissue.

For example, a bacterium can connect with its pilus to another bacterial cell. Now, when the bacterium retracts the pilus, it pulls the other bacterium closer. Like this, bacteria can form aggregates which helps them in the first steps of settling down and building biofilm houses.

Also, when several bacteria stick together and form bigger groups, they can move along a surface in a coordinated manner. This helps bacteria conquer new environments quicker and find new resources. For example, the bacterium Pseudomonas aeruginosa can reach out in swarms trying to find more space and new places to live in.

Interestingly, multicellular Myxobacteria move as huge cell aggregates to attack their prey. These bacteria use their twitching pili to glide along a surface, attach to a prey and pull the whole aggregate towards the prey. Like this, the Myxobacteria quickly run over their prey so it does not stand a chance.

However, bacterial pathogens also use pili to infect us. The bacterium Neisseria gonorrhoeae can attach its pilus to human epithelial and endothelial cells. When the bacterium then retracts the pilus, it pulls itself closer to the cell and attaches to it more tightly. Now, it can infect the cell and eventually the host.

But not all is lost with bacteria and their pili. Currently, researchers are trying to better understand how bacteria use their pili and how this machine works mechanistically. They will then try to find drugs that inhibit the pili. This could be an alternative way to inhibit bacterial pathogens and maybe even drug-resistant bacteria.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world