So, when we take antibiotics because of a bacterial infection, billions of bacteria are suddenly attacked by antibiotics.

They struggle to repair damage, maintain their structures and continue essential functions just to stay alive.

This ultimately weakens or kills the cells.

And as you can imagine, this is pure stress for the bacteria.

One that we take advantage of.

This article series takes you on a journey through the microscopic war between bacteria and antibiotics. Across five articles, we will explore how antibiotics attack bacteria, how bacteria overcome them, become resistant and how evolution pushes bacteria to survive the antibiotic war.

In this first part of the series, we explore how different classes of antibiotics work, while focusing on the most commonly used antibiotics. Once you understand these mechanisms, you will better understand how and why bacteria fight back, evolve and develop resistance.

Antibiotics attacking bacterial cells by stopping cell division

Bacteria have a rigid cell wall made of peptidoglycan to maintain their shape and internal pressure and to protect them from the environment. Without the ability to build or repair the cell wall, bacteria become fragile and burst easily.

This vulnerability is precisely what antibiotics from the β-lactam family exploit. You have probably heard of penicillin, one of the most well-known members of this class. Other similar antibiotics are amoxicillin and cephalosporins.

How these antibiotics work is pretty simple but devastating to bacterial cells: they block the so-called penicillin-binding proteins. These enzymes sit in the cell wall where they are responsible for building and cross-linking it.

So, when a bacterium gets hit by a β-lactam antibiotic, it loses the ability to divide. Basically, every time it tries to divide, it will burst like a water balloon.

Antibiotics sabotaging bacteria’s genetic machinery

Every bacterial cell carries instructions for life in its DNA, the molecule that stores genetic information. Before dividing, bacteria copy their DNA and then share it with their daughter cells.

Bacteria also make RNA, the molecule that executes the instructions stored in DNA. RNA comes in different types with distinct roles, but it is fundamentally needed to make proteins from DNA.

Some antibiotics exploit this vulnerability by inhibiting one of the cell’s information-processing machineries. This fundamentally interferes with DNA or RNA synthesis. If a bacterium can’t produce DNA or RNA, it can’t divide or maintain its genetic integrity, leading to cell death.

The antibiotic class fluoroquinolones inhibits DNA production. For example, ciprofloxacin freezes the enzymes that help bacteria copy their DNA. When DNA replication stalls, bacteria cannot divide. They accumulate damage and eventually die.

In comparison, rifamycins inhibit RNA synthesis. These antibiotics bind to the RNA polymerase, the enzyme that produces RNA from DNA. They thereby block the first step in protein production.

It’s like cutting electricity to an entire factory; without RNA, the cell cannot produce proteins, halting metabolism and growth. This is highly stressful to bacteria and can quickly kill them.

Antibiotics blocking protein production: The ribosome hijackers

Other antibiotics directly inhibit the protein production step: To build proteins, bacteria produce a temporary working copy of those DNA instructions, the so-called messenger RNA or mRNA.

This molecule travels to the ribosome, which reads the mRNA and makes proteins from it. Since proteins are essential for metabolism, movement, growth and cell division, no cell can function without them.

Some antibiotics, like tetracycline, take advantage of this protein production vulnerability. By interfering with ribosomes, these antibiotics prevent them from producing proteins and eventually the bacterial cells from functioning.

Interestingly, not all protein-production inhibitors kill bacteria in the same way. Some antibiotics are bacteriostatic, which means they freeze growth without immediately killing the cell. The bacteria cannot make new proteins, so they can’t divide or repair themselves. Instead, the existing proteins remain active for a while, allowing the cell to survive in a weakened state.

Others, like aminoglycosides, are bactericidal. Instead of simply blocking ribosomes, they cause the ribosome to make mistakes and produce misfolded proteins. These faulty proteins build up inside the cell and damage essential structures, overwhelming the bacterium, so it eventually dies.

Antibiotics disrupting metabolic pathways

Lastly, some antibiotics target essential metabolic pathways that bacteria need to survive. For example, folate is an essential vitamin that all organisms need to grow and reproduce, and most bacteria have proteins to make their own folate. So, when antibiotics block these folate-producing proteins, the bacterium will eventually run out of folate and lose the ability to grow.

How different antibiotics kill bacteria

As we’ve seen in this post, antibiotics can impact bacteria in many different ways. But they all have the same goal: do the biggest damage possible. Antibiotics can damage a bacterium’s DNA, its protein production machinery, metabolic pathways or the cell envelope.

This damage is essentially stress for the bacterium: they must repair the damage or adapt their metabolisms to it. If they cannot cope with the damage or the stress, they’ll die. And remember, this was basically the antibiotic’s goal from the beginning.

But be aware: this stress can be both lethal and a driving force for bacterial evolution. As they learn to cope with the antibiotic and the stress, they become resistant. And in future articles, we will explore these bacterial learning processes and how they help make bacteria resistant to antibiotics.

The post How Antibiotics Kill: The Weapons We Use Against Bacteria appeared first on Bacterialworld.
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.

The post How your immune system battles harmful bacteria every day appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

And only thanks to pigments, life on Earth is possible. Pigments were the first molecules that microbes used to harvest sunlight. Microbes could then transform the light energy into chemical energy and produce oxygen.

Even the brown-reddish haemoglobin in your blood is an essential pigment as it transports oxygen within your body. Also for bacteria, pigments and their colours have life-saving functions. Here, we will look at how biopigments colour the bacterial world and what bacteria gain from producing them.

Bacterial pigments bring colour to the world of bacteria

Biopigments are molecules with complex chemical structures and at least one excited electron. Depending on the electron’s arrangement, a pigment absorbs light at a specific wavelength. It reflects the colour of the unabsorbed wavelength, which gives the pigment its colour.

As the function of pigments depends on the incoming light, sunlight plays a crucial role for bacteria with pigments. By adding certain pigments to their membrane, bacteria can adapt to environments that are directly affected by sunlight or the lack of it. This gives them an advantage over those bacteria that lack these pigments.

However, some bacteria also use pigments for other purposes, which we discuss further in this article.

Microbes harness photosynthetic power with colourful pigments

Sunlight is incredibly powerful since each light photon contains energy. Bacteria adapted to harvest energy from sunlight with special pigments.

Pigments can capture the incoming photon and transfer its energy to other molecules. This process transforms the incoming light energy into chemical energy. So-called phototrophic microbes are those that gain their energy from light.

The best-known example of a photosynthetic biopigment is chlorophyll in plants, algae and cyanobacteria. Cyanobacteria produce several complexes of bacteriochlorophylls to absorb blue and red light. As the green light is not absorbed, it is reflected, which is why chlorophyll – and thus cyanobacteria, algae and plants – are green.

Some bacteria harvest more light by producing several pigments of different types. They then arrange them in an optimal formation according to the incoming light.

For example, carotenoids capture energy in the green-blueish range and pass it on to the associated chlorophyll. Together, these photosynthetic complexes absorb light energy from almost the entire wavelength spectrum.

Halophilic bacteria and archaea are microbes that produce carotenoids to capture sunlight. You may have seen salt ponds with a reddish colour. This comes from the red and pink-coloured archaea Halobacteria, bacteria Salinibacter or algae Dunaliella. Thanks to their colourful carotenoids, these microbes adapt to salty waters that are exposed to direct sunlight.

Cyanobacteria in the deep sea, lagoons, lakes, ponds or rivers produce similar molecules to chlorophyll. These absorb the blue-green light in water, which allows these bacteria to survive in these dark environments. If you have ever seen a lagoon shining yellow or orange, this was probably due to the colourful cyanobacteria inside.

Bacterial biopigments protect from too much light

As light is full of energy, bacteria also need to protect themselves from getting burned. For this, they produce pigments that take up the excess light energy. Like this, the main photosynthetic complex does not get damaged.

Carotenoids and xanthomonadins are the colourful sun blockers of the microbial world. These molecules absorb high-energy light to protect chlorophyll from damage. Over 600 different carotenoids were described and they usually come in yellow-orange-reddish colours.

The yellow xanthomonadins absorb wavelengths within the energy-rich UV spectrum. Bacteria like Xanthomonas campestris live on plant leaves where they are exposed to direct sunlight. Hence, their yellow xanthomonadin coats are like self-made sunblocks protecting the bacteria.

Also, the pigment melanin shields the producing cell from energy-rich sunlight. Many bacteria living in the soil or bacterial spores produce these pigments. Here, melanin absorbs light from a wide range of the light spectrum to protect the inner of the cell. Hence, melanin-producing bacteria, like Vibrio cholerae and Streptomyces bacteria, are brown or black.

Bacterial pigments let electrons flow and save energy

Since bacterial pigments allow electrons to flow, they can also be energy conductors. Hence, some pigments are important components of energy complexes and synthesis machineries.

For example, yellow flavins are pigments involved in cellular metabolism. The main flavin is riboflavin, which you may know as vitamin B12. This essential molecule – produced only by bacteria – allows our bodies to work.

Phenazines are unique bacterial pigments with yellowish-green fluorescent colours. Pyocyanin, exclusively produced by Pseudomonas bacteria, shuttles electrons – and thus energy – during the respiration process. Hence, pyocyanin is essential for Pseudomonas as it keeps the bacteria healthy and alive.

Some biopigments have anti-oxidant effects

Bacterial pigments don’t just help adapt to external environmental conditions like the sunlight. They also guard the inner bacterial cell from stressful situations.

Excess or uncaptured energy or escaped light photons can react with oxygen. This process produces so-called oxygen radicals, which can damage molecules inside the bacterium. Known as oxidative stress, oxygen radicals can even become life-threatening for bacteria.

Carotenoids and xanthomonadins protect bacterial cells from oxidative stress. These pigments transform the free oxygen radicals into harmless molecules. Since carotenoids and their product vitamin A have similar functions in humans, it is only healthy for us to take up a lot of these with our diet.

In the bacterium Gemmatimonas aurantiaca, orange carotenoids also work like sunscreen and oxidative shield. These pigments both give the bacterium its bright orange colour and protect it from too much sunlight.

Bacteria combat microbial enemies with coloured pigments

As night falls, many bacterial pigments reveal their darker sides. They become important weapons for microbial warfare. Without sunlight, several pigments take on roles as virulence factors and antimicrobials as they mess up cells’ energy and oxygen household.

For example, prodigiosin is the red weapon of Serratia marcescens. As prodigiosin inhibits the growth of several bacterial, fungal and insecticidal pathogens, Serratia marcescens is an important biocontrol bacterium of plant disease.

You may have seen prodigiosin-producing Serratia bacteria on contaminated food. They develop these red, blood-like dots.

Violacein is a purple pigment with anti-viral, anti-bacterial and anti-cancer properties. For example, Chromobacterium violaceum sends membrane bubbles filled with violacein to kill bacterial enemies.

Similarly, Janthinobacterium lividum protects frogs and salamanders as it lives on their skins. Here, the bacterium throws violacein at pathogenic fungi that would otherwise infect and harm the animals.

Pyocyanin, the fluorescent electron-shuttling pigment in Pseudomonas, is also very sensitive to oxygen. It even turns Pseudomonas aeruginosa cultures in the lab blueish just by shaking and airing them.

Yet, not all bacteria have an appropriate coping mechanism for pyocyanin. Hence, these bacteria suffer oxidative stress when they come into contact with this pigment. This is why Pseudomonas uses pyocyanin also to fight bacterial and fungal enemies.

Vivid pigments colour the bacterial world

The Bacterial World is colourful – one of this blog’s taglines. You may have asked yourself what this is about and why bacteria have so many different colours.

From the dazzling pink of halophilic microorganisms to the sunny yellow of phytopathogens, bacterial pigments give their producers shiny and vibrant colours. But thanks to the colourful biopigments, bacteria also gain abilities to survive in new and challenging environments.

Some of these bacterial pigments are essential for us humans and even life on Earth. From some of these colourful biopigments, we produce vitamins that we need for our own metabolism. Also, every oxygen molecule that you just took up with your last breath, at some point, was transformed by a bacterial chlorophyll pigment.

So, I guess it is yet again time to be grateful to bacteria and their vibrant and life-enabling activities!

The post Creating the colours of the rainbow: Bacteria and the vibrant world of pigments appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

And some of these microbes learned to adapt to these special – or extreme – conditions. They can’t even cope in normal environments.

Extreme conditions or extreme environments can be anything that we consider uninhabitable for us. This can be extremely high or low temperatures, extremely high or low pressure, radiation or toxicity.

Some of these microbes actually love the extremes. And these so-called extremophiles have special superpowers that help them survive in hostile places – like the bottom of the sea.

What are extremophiles

For example, so-called thermophiles live and grow at temperatures above 50 °C and hyperthermophiles even at temperatures above 80 °C. On the other hand, psychrophiles love temperatures below 10 °C. Plus, researchers keep finding interesting new species in the permafrost soils of the Arctic and Antarctic.

Some extremophiles also have superpowers to survive in extremely salty or acidic places like saline lakes or acid mine drainages. And other extremophile microbes grow in places with high metallic or toxic concentrations or high pressure like at the deep sea of the ocean.

These extreme environments put a lot of pressure on microbes, which means they need to adapt to these conditions or they won’t survive. Hence, in these extreme environments, microbes are mutating more often or exchanging more DNA with other species to learn to cope with these challenging conditions.

Here, we will look at microbes and extremophiles that live and grow in the deep sea. In this dark place, microbial communities have developed fascinating mechanisms to adapt. And from here, they can also impact our global climate.

Extremophiles living in the deep sea

Imagine the bottom of the sea about 30 km underwater: It is dark since sunlight cannot shine this far. It is 2 – 3 °C cold while close to hydrothermal vents, it can be up to 400 °C all of a sudden. And the pressure at the sea bottom is extremely high since all that water is extremely heavy pushing everything down.

And yet, the bottom of the sea is full of happily-living, growing microbes that enjoy their times together, feeding each other and stabilising our ecology. These microbes can swim around in the open sea. Most of them attach to dirt or sediment particles on which they form biofilms.

As you can imagine, this environment doesn’t offer much food or energy. So, it is incredibly important that microbes interact with each other here to exchange meals and information. That’s why many microbes in the deep sea feed each other with one microbe producing a special substrate that another microbe likes to eat.

These microbial food webs are very important for our global nutrient cycles as deep-sea microbes sequester atmospheric gasses, like CO2, and degrade contaminants and pollutants. For example, thermophilic bacteria like Desulfovulcanus ferrireducens and Oceanithermus profundus live close to hydrothermal vents which is why they grow best at about 65 °C. These extremophiles get their energy from hydrogen gas and organic acids that swim in the ocean.

Also, during oil spillages in the ocean over recent years, researchers found many bacteria and fungi that can eat and degrade oil or petroleum. Hence, their need for food cleans our oceans of these harmful components.

How extremophiles adapt to the deep sea

The deeper you are in the ocean, the less oxygen is available for microbes to breathe. Hence, microbes had to become creative about where to get their energy from. For example, Desulfovulcanus ferrireducens mainly uses iron components for respiration and growth while Oceanithermus profundus prefers nitrogen gas. All over the oceans, there are SO MANY microbes eating these iron components and nitrogen gas. Hence, all their metabolic activities impact the iron and nitrogen cycles of the whole planet.

But microbes and bacteria in the deep sea did not only have to adapt their meals to these conditions. Deep-sea extremophiles also had to develop mechanisms to withstand the pressure and the cold of this hostile place.

At very low temperatures, proteins often get out of shape so that they lose their functions. This can mess up the whole bacterial cell, which is why psychrophilic bacteria have so-called chaperones that constantly check the bacterium for proteins that are out of shape. These chaperones then help the protein get back into normal shape and thus to its normal functioning state.

Extremophile bacteria have different membranes

Another way to adapt to hot and cold temperatures is for bacteria to change their membranes. As you might know from experience, fat gets solid when it’s cold and fluid when it’s hot. And since bacterial membranes are mainly made out of lipids and fats, thermophilic and psychrophilic bacteria need to make sure their membranes can cope with the extreme temperatures.

To prevent membranes from becoming too fluid and leaky at high temperatures, thermophilic microbes solidify their membranes. On the contrary, psychrophilic bacteria like Psychromonas and Marinomonas need to make sure that their membranes stay flexible at cold temperatures.

Luckily, this special cold-adapted membrane also helps bacteria withstand the high pressure in the deep sea. And to counteract the pressure inside the cell, piezophile bacteria produce a lot of stuff and basically crowd their cells with proteins. This aims to keep the cell pressure inside high against the high pressure from the outside.

However, investigating such high pressure is extremely difficult in the lab. That’s why researchers still don’t know much about the pressure adaption of extremophiles in the deep sea.

What we can learn from extremophiles in the deep sea

Even though we still don’t know much about the fascinating microbial life underwater, researchers are optimistic that they will find lots of helpful microbes. Whether adapted to the cold or to the heat, deep-sea microbes have incredible mechanisms to grow at extreme temperatures.

This means they contain proteins that function perfectly on either side of the temperature spectrum. So, researchers hope that we could use that knowledge to design tailor-made proteins for our daily lives. We could for example use them in households or in biotechnology applications, for example, to improve cleaning efficiency or reduce energy input.

Another important aspect is to explore how microbes in the deep sea affect our global climate. With climate change, our oceans are getting warmer and thus they contain less oxygen. This means that also microbes are likely adapting to these changes which in turn influences the global climate.

Hence, understanding how microbes cope with the conditions in the deep sea helps us comprehend the full impact of climate change. This might then give us an idea about how to prevent more damage to our beautiful planet. With the help of microbes.

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

Energy to grow, to move, to fight, to produce stuff and also to reproduce.

Generally, living organisms get this energy from food. It fuels us, just as it fuels animals, plants and bacteria.

But where exactly is this energy in food? How do bacteria and other living organisms access this energy? And what do they do if their favourite food is not around?

To answer these questions, let’s look at how molecules store energy.

How do living organisms gain energy?

Each chemical bond between atoms contains energy. Hence, a molecule that is made of many atoms and thus many chemical bonds, contains energy. When such a chemical bond opens, it releases energy in the form of electrons.

Depending on the kind of chemical bond within the molecule, these electrons can have higher or lower energy levels. Thus, they contain more or less energy.

So, to obtain energy from molecules, organisms need to break apart molecules and extract the electrons with high energy. But this is not as easy as it sounds. Chemical bonds are quite tight and it actually requires energy to break them open.

Hence, organisms need to have the right sets of proteins that can break open specific chemical bonds in molecules. These kinds of proteins are called enzymes. So, only if an organism has enzymes to break apart glucose, it can use glucose to extract its electrons and obtain energy.

Interestingly, most organisms do exactly that. They break apart glucose into smaller products and take the freed electrons. In that case, glucose is the so-called electron donor.

Now, these electrons need to go somewhere, since they are full of energy. So, organisms save this energy by transferring these electrons onto other molecules. These molecules have lower energy levels, hence they like to take up electrons. We call these molecules electron acceptors.

But finding the right electron acceptor is not as easy as it sounds.

The many steps from an electron donor to an electron acceptor

Imagine you stand on a high wall and want to get down onto the ground. You could take one big jump to reach the ground. But then you would risk that this high fall would give you so much energy that you might break your knees.

So, you could take a set of stairs, that brings you to the ground in multiple steps. Each step only releases a small chunk of energy but they would definitely not hurt you.

It is the same with electrons from donors with a lot of energy. Transferring these electrons to a final electron acceptor would free up too much energy at once. This could actually burn a cell. Hence, organisms transfer these electrons onto intermediate electron acceptors.

Each of these transfer steps only releases a small chunk of energy that keep organisms warm but also fuel cellular processes. In bacteria, these transfer processes happen in their membranes, where the released energy is directly used.

Here, the released electrons energise flagella so that bacteria can swim. Electrons can also activate transporters so that bacteria can import or export stuff. Not needed electrons and their energies are stored in energy-saving molecules like ATP.

This whole process of electron transfer from a donor to its final acceptor is generally what researchers call cellular or – more specifically – bacterial respiration.

Which molecules do bacteria use for cellular respiration?

Cellular respiration fuels most living organisms. And glucose is a molecule with one of the highest energy levels. Hence, breaking down glucose to extract its electrons is the most common in living organisms.

Animals do it. Fungi do it. So, bacteria are no exception to it.

And as a final electron acceptor, most organisms use oxygen. This molecule has a very low energy level and is basically everywhere so most organisms transfer their electrons to it.

This is what we call aerobic respiration (which is what we generally do as well). But it comes with great risk.

The downside of aerobic bacterial respiration

As soon as an oxygen molecule is fuelled with just one electron, it becomes hyperreactive. Such a semi-activated oxygen molecule can basically react with any compound in a cell and damage it.

This is what makes aerobic respiration quite dangerous. So, every organism aims to hide these reactive oxygen molecules in the membrane.

Yet, it can happen that such a reactive oxygen molecule escapes the membrane. In this case, a special protein binds it and breaks it apart. So, every organism that does aerobic respiration has this same kind of protective protein to get rid of reactive oxygen molecules.

This means that whenever scientists find a new microbe, they first test whether this new microbe has these proteins. To test this, they add a bit of hydrogen peroxide to the bacterial colony. When bubbles come out of the bacteria, it means that they do aerobic respiration. In this case, they have the enzymes to break apart the reactive oxygen molecule and produce oxygen from it.

Which other molecules can bacteria use as energy source?

As we said, most bacteria use glucose as an energy source for cellular respiration. However, there are also many fancy exceptions. And these exceptions make the bacterial – and microbial – world so colourful and diverse.

While many bacteria can extract electrons from many different organic acids and amino acids, some use sulphur compounds. Some bacteria also break apart greenhouse gases like methane, carbon monoxide or even hydrogen gas. Since these bacteria might be helpful in tackling our climate problems, they are of particular interest to researchers!

What does bacterial respiration look like without oxygen?

We surely need our oxygen for respiration. Yet, many bacteria and fungi can live with only small amounts of it or even no oxygen at all.

In this case, they do anaerobic respiration. This basically means that they don’t transfer their electrons to oxygen as an electron acceptor.

Instead, many bacteria have enzymes to transfer their electrons to different electron acceptors. And these depend on what the bacteria have available around them. These electron acceptors can be nitrate or sulphate compounds, salts like arsenate or even metals like iron and gold.

Also, in many microbes, anaerobic respiration is closely related to microbial fermentation. In this case, the bacteria break apart glucose but produce molecules that do not require oxygen.

Just think about yeast that produces ethanol in beer and wine. Or lactic acid bacteria in your sauerkraut and yoghurt that produce lactic acid to make the food more acidic. Lastly, there are fungi like Zymomonas mobilis that produce huge amounts of ethanol from glucose.

Bacterial respiration makes the microbial world diverse

As we have seen, bacteria learned to use various sources to gain energy. They created the right enzymes to extract electrons from fancy high-energy molecules.

And then they learned to transfer these electrons onto even fancier molecules to gain the most energy. Some of these processes even involve bacteria producing shiny gold!

In my opinion, these truly amazing superpowers make the bacterial world so incredibly colourful and fascinating!

The post How bacteria gain energy from cellular respiration to fuel life appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

So, they talked of cocci and bacilli based on the spheres and rods that they saw under the microscope.

And they classified microbes and bacteria based on these shapes.

It came only with later, modern technologies that scientists learned that there was more to bacteria than their shapes. Even though bacteria looked similar, they had different superpowers.

Yet, some of these bacterial superpowers are indeed influenced by their cell shapes.

So, what is it about bacterial shapes? Why do bacteria look differently? And how do the different shapes of bacteria help them survive and thrive?

What gives bacteria their shapes?

To protect themselves from the environment, bacteria as well as all other organisms have cell envelopes. These keep the cellular machines and internal parts together so that a bacterium can function within this envelope.

And this envelope also gives bacteria their shape.

Both Gram-positive and Gram-negative bacteria have a layer of so-called peptidoglycan within their envelope. This peptidoglycan layer is made of sugars that are linked together by very strong bonds. This is why the peptidoglycan layer is pretty rigid and stiff and has a specific shape in each bacterium.

Either on the inside or on the outside, the peptidoglycan layer is linked to the cellular membranes. Together, these make up the bacterial envelope with a specific cell shape.

What different shapes do bacteria have?

Microbiologists have different ways to classify known bacterial shapes. Here, I will introduce you to the bacterial shapes according to what makes the most sense to me.

Rod-shaped bacteria

As the name suggests, these bacteria have a rod or cylindrical shape. Examples of rod-shaped bacteria are Escherichia coli and Bacillus subtilis.

Scientists are also convinced that rod-shaped bacteria are the evolutionary ancestors of all other bacterial shapes.

The shape comes from proteins that form long cables within the bacterial cell. These span out the whole bacterium from one end to the other.

Rod-shaped bacteria grow by two modes that we talk about in Why bacteria divide into two and grow with the help of a strong ring: First, they extend their cell size by growing the peptidoglycan, the cable proteins and the membrane.

Second, the cable proteins determine the middle of the cell, where the bacterium produces a special ring. Eventually, this ring narrows so that the bacterium divides and two bacterial cells form.

Spherical bacteria

The spherical bacteria – or so-called cocci – include many pathogenic bacteria like Staphylococcus aureus, Streptococcus pneumoniae and Neisseria gonorrhoeae.

Microbiologists think that spherical bacteria were once rod-shaped as well. However, spherical bacteria do not have these long cable proteins that extend their cell bodies. Thus, they stay spherical and grow by dividing their spherical cells right in the middle.

However, sometimes the two daughter cells do not completely divide and they stay attached to each other. This is why some spherical bacteria live as so-called diplococci.

Curved bacteria

Curved bacteria have the shape of a comma or banana and are sometimes also slightly twisted. Examples of curved or banana-shaped bacteria are Caulobacter crescentus and Vibrio cholerae.

These curved bacteria usually live in watery environments where there are flows. Here, the curved shape helps the bacteria to align with the flow while staying attached to a surface.

In the case of Caulobacter crescentus, one end of the bacterium is glued to a surface with a strong super glue. When this bacterium divides in the middle, one daughter cell remains attached to the surface, while the other one can swim away and find a new location to settle down.

Spiral bacteria

Spiral bacteria are a mix of rods and curves which give them a helical twist. Hence, these bacteria have a corkscrew shape.

Many pathogenic bacteria use their corkscrew shape to swim through gel-like solutions. This includes Helicobacter pylori and Campylobacter jejuni.

Since spiral – or helical – bacteria are also thinner, they can reach locations that are too narrow for other bacteria to reach. They also use their flagella to push themselves forward and “wriggle” through narrow pores.

Star-shaped bacteria

Some bacteria look even fancier than others: They are real stars – yes, bacteria with a star shape.

While we don’t know much yet about star-shaped bacteria, they belong to the so-called Stella species or are Methylomirabilis oxyfera. These usually grow in freshwater, soil and sewage.

The star shape comes from six little arms that extend out of the bacterial cell. These push and grow to the outside giving these bacteria a shiny star shape.

Why do bacteria have different shapes?

Now that we have seen the different shapes of bacteria, you might ask yourself, why do bacteria have these different shapes? How do they help them?

As always in biology, it comes down to how a property helps a bacterium survive in a certain location. Often, the cell shape gives a bacterium advantages over other bacteria and it is easier for them to settle down and face harsh environments.

For example, spherical cells have the lowest surface-to-volume ratio. This means they have a large envelope surface through which they can take up a lot of nutrients. All this while their cell volume is relatively small. So they don’t actually need that many nutrients. This helps cocci to grow in locations where there are little amounts of nutrients.

On the other hand, rod-shaped bacteria often have flagella. And thanks to their shapes, they are efficient swimmers. This allows them to swim to new places in cases of danger or the lack of nutrients.

Bacterial cell shapes help face harsh environments

Also, straight rod cells can pack into biofilms more efficiently and build organised structures. This helps them colonise different locations and resist dangerous environments.

Many rod-shaped bacteria also form longer filamentous organisms. These stronger and larger structures protect bacteria from being eaten by other organisms. Another advantage of these multicellular organisms is that they allow more cells to attach to surfaces and colonise hosts.

Lastly, both curved and helical bacteria use their shapes to get better around their environments. Curved bacteria grow in watery environments but also in our guts. Here, their shapes help them align with the flow of water or our gut content while they stay attached to a surface or the gut wall. This keeps them at their preferred location and protects them from being flushed away.

Spiral bacteria use a fascinating helical movement to screw through gel-like or viscous fluids. This for example helps pathogens swim through the mucus of our stomach and guts and colonise us and make us sick.

Bacteria and their shapes

Here, we looked at the different shapes that bacteria have and how these help them survive. Bacteria always face harsh and new environments and conditions and only survive if they have the right tools or means.

So, by adapting their shapes, bacteria often have advantages over other bacteria. Plus, they look cool and fabulous!

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

Also, bacteria want to grow and flourish and reproduce. But they are only single cells so that their way of reproduction is unique. They reproduce asexually meaning you only need one parent bacterium to make two daughter bacteria.

When you think about it, bacterial cell division seems very easy: Start with one bacterium, divide it in the middle and you end up with two.

However, the mechanism of cell division is pretty complex and involves at least three tasks:

• the bacterium needs to decide WHERE to divide
• get all the needed machinery to the division site
• produce new cell envelope material to separate the two new daughter cells

How a bacterium starts cell division

As you can imagine, for most bacteria it makes the most sense to divide straight in the middle. Like this, they end up with two daughter cells of the same size.

This means a bacterium needs to find its middle and mark it. While it is not completely clear yet to researchers how bacteria find the exact middle, they know it involves a so-called Z-protein.

This Z-protein can bind two things: itself and the inside of the bacterial cell envelope. But it only binds the cell envelope where it is straight and not bent. And this is only the case in the middle of the bacterial cell envelope.

Hence, the Z-proteins bind themselves in a long chain linked to the straight cell envelope. Eventually, they form a ring on the inside of a bacterial cell. And this so-called Z-ring stays in the middle of the bacterium.

Also, the Z-ring is only stable when bacteria have enough nutrients and do not encounter any stress situations. This reassures that bacteria only divide when they have all the needed supplies.

How bacteria divide and produce two daughter cells

Once this Z-ring is stable, it recruits helper machineries to this now defined division site.

The Z-ring is a sign of an upcoming cell division. Now, the bacterium knows it needs to activate machineries to produce more cell envelope material and become longer. And to increase their cell envelopes, bacteria use ferries, tunnels and bridges to transport lipids into the cell envelope.

Like this, the bacterium becomes longer and can start the actual cell division. At the same time, the Z-ring becomes tighter and the cell envelope gets its natural bend again.

Now, two processes happen at the same time: Bacteria cut open their peptidoglycan envelope to separate the two daughter cells and also produce envelope material to close both cells.

After this happened, we have two daughter cells coming from the same parent. They both share the same cell envelope and genome. This is why we consider them identical twins.

But do all bacteria produce identical twins upon cell division?

Do bacteria always divide in the middle and produce identical daughter cells?

Yes, most bacteria are symmetrical. And when they divide right in the middle, they produce two identical daughter cells.

Researchers could even watch bacteria during this process thanks to amazing microscopy techniques. You can see the single stages of bacterial cell division and how bacteria produce the cell envelope in the image below.

Yet, the bacterium Caulobacter crescentus has two different cell ends. It can stick to a surface with its sticky stalk on one end and have flagella on the other.

This bacterium also starts cell division in the middle like what we discussed above. However, the new daughter cells are now different: one is still glued to the surface and the other one has flagella and can swim away.

Also, the bacterium Helicobacter pylori with its helical shape can never really find its perfect middle. Hence, the Z-ring forms somewhere inside the bacterium and its daughter cells always have different sizes.

And then there are funny bacteria that decided they don’t even need to divide in the middle. Bacteria like Gemmatimonas aurantiaca grow “budding” daughter cells out of their own parent cells. However, researchers don’t understand yet why this bacterium chooses to divide in this asymmetric way.

Another way of asymmetric cell division happens in the bacterium Bacillus subtilis when it produces spores. During the sporulation process, the spore daughter cell grows within the mother cell. In the end, the mother cell bursts to release the spore into the environment. In this case, only one daughter cell comes out of the division process.

Why and how we want to prevent bacteria from dividing

Since cell division is an essential mechanism for bacteria, nature also found ways to inhibit it. Many antibiotics or toxins inhibit the production of cell envelope material or of the Z-ring. Like this, bacteria cannot divide anymore; they cannot grow and die.

However, we also know that some bacteria can find ways around the toxicities of antibiotics or toxins and become resistant to them. Hence, by better understanding how the whole mechanism works, researchers can hopefully find new ways to interfere with bacterial growth and find new weapons in the fight against antimicrobial resistance.

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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

However, some bacteria found a way to become invisible in front of the immune cell army. They put on an invisibility cloak so that they can sneak into the human body without being seen. This invisibility cloak is a so-called bacterial capsule. And pathogenic bacteria use capsules to trick the immune system to infect our bodies.

Here, we will explore what bacterial capsules are and how bacteria use them to overcome our immune systems.

About bacteria with capsules

Bacteria that produce capsules are generally pathogens. These are bacteria that can infect us, cause disease and make us sick. And bacterial pathogens use capsules for the infection process. Without capsules, pathogenic bacteria would be eaten and killed by our immune cells.

Bacteria with capsules are for example Klebsiella pneumoniae, Mycobacterium tuberculosis, Haemophilus influenzae, pathogenic and uro-pathogenic Escherichia coli, Neisseria meningitidis and Porphyromonas gingivalis.

Many people carry Klebsiella pneumoniae in their gastrointestinal tract or nose without having any symptoms. However, in some people, this bacterium can enter the blood circulation and cause infections like pneumonia, sepsis, urinary tract infections, bacteremia or meningitis.

The pathogen Mycobacterium tuberculosis causes the devastating disease tuberculosis with almost 1.4 million deaths every year. Haemophilus influenzae infections lead to sinusitis and uro-pathogenic Escherichia coli causes urinary tract infection. Another awful pathogen is Neisseria meningitidis. This bacterium infects the membrane around our brain and leads to the disease meningitis. Lastly, Porphyromonas gingivalis is an oral pathogen that infects and destroys the tissue around our teeth. You might know this disease as periodontitis.

This list of pathogenic bacteria might sound a bit frightening. But it is to highlight the one feature they all have in common: These bacteria use their capsules to enter our bodies and cause these diseases.

So, let’s have a look at what this capsule actually is.

What are bacterial capsules

The bacterial capsule is a thick layer of a sugar-water mix that surrounds the bacterial cell.

The capsule layer consists of long chains of sugar molecules that are attached to the bacterial cell surface. These sugar molecules have different lengths, lots of branches and different attachments. The sugar chains absorb water molecules so that a gooey slime develops. Researchers can even see this under the microscope.

Interestingly, different bacteria can produce chemically identical capsules. But the same bacteria can also produce different capsules. In this case, bacteria add little attachments to the outer tip of their sugar branches. Now, this bacterium “looks” completely different from the outside.

Generally, antibodies bind to these sugars, which is why we call these sugars antigens. However, when bacteria change their sugar tips, they also change their antigens. Hence, another antibody is needed to recognise this new antigen – even though it might still be the same sugar. In this case, we call the bacterium with the new sugar antigen a serotype.

For example, researchers found 80 different antigens and thus serotypes in Escherichia coli based on their capsule sugars. And for Streptococcus pneumoniae, they even identified 93 serotypes.

Now, you might ask yourself what is the function of capsules in bacteria?

Bacterial capsules are invisibility cloaks

A bacterial capsule works like an invisibility cloak. As soon as a bacterium enters the dark halls of our human bodies, it puts on the cloak. Now it won’t be seen by the immune guardians. Like this, bacterial pathogens follow the model of “the best defence for a pathogen is a good defence”.

The players of our immune system recognise and bind to specific molecules on the surface of bacteria. This activates the immune system and attracts more phagocytes. These immune cells eat intruding pathogens and destroy them. Like this, our immune army is always ready to fight the bad guys.

However, the bacterial capsule hides these surface molecules that our immune system usually recognises. Like this, our immune players cannot bind these sugar-coated pathogens. This keeps the immune army deactivated. Now, bacteria can escape the immune system, sneak into our bodies and cause infections.

Our immune system can also fight intruding bacteria by producing antimicrobials. Yet, the sugar capsule of some bacteria can absorb these small molecules and make them useless. Hence, the bacterial capsule acts as a protective layer against immune attacks.

Neisseria meningitidis even has a “capsule-switch”. Once activated, it can cover itself with another sugar layer that looks completely different from the outside. The immune players need to learn again to recognise this new layer, which takes time. Hence, with this “hyper-encapsulation”, Neisseria meningitidis can escape the immune system again.

Overcoming bacterial capsules

Because bacterial capsules are at the outer surface of a bacterium, researchers want to use these components as targets for vaccines. However, since bacteria can change their capsular components, these targets are not very reliable. So, researchers are working on developing vaccines that recognise different serotypes.

For example, a vaccine that recognised different antigens of the capsule in Klebsiella pneumoniae was developed and reached clinical trials. However, the high costs of such an efficient vaccine made this project difficult.

Another approach is to better understand how pathogenic bacteria regulate their “capsule-switch”. If we can prevent bacteria from putting on another cloak, we can help our immune system do its job and kill intruding bacteria. Hence, researchers are looking for ways to achieve this.

Bacterial invisibility cloaks – another way for bacteria to survive

You might now think how nasty bacteria are for using such a capsule to escape our immune system and infect us. However, for bacteria, this is another survival mechanism. If they do not put on their invisibility cloak, the immune system will eat and kill them. So, some bacteria developed this mechanism to overcome their foes.

And I think it is a pretty smart way to survive.

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

For a virus to survive, it needs another living organism. Viruses infect any organism that has its own metabolism: animals, humans, fungi or even bacteria.

But none of these organisms likes being infected by a virus. It makes them sick.

Therefore, each organism developed its own way to fight off viruses. For example, you have your immune system that is trying to protect you from bad viruses.

And so do bacteria.

The bacterial immune system is not as complex and sophisticated as ours. But still, bacteria developed several mechanisms to fight off viruses and protect the community.

Here, we will look at the different ways of how bacteria become immune to viruses.

How a virus infects a bacterium

First, let’s have a look at how a virus infects a bacterium and reproduces.

Most viruses can only infect one specific bacterium. This is because each bacterium has a slightly different coat around its cell. And viruses recognise specific components on the outside of these coats.

When a virus binds to such a specific component on the bacterium, it cuts a little hole into the coat. Now, the virus can inject its genome through the hole into the bacterium.

The bacterium recognises the genome and starts producing virus particles from the viral genome.

After the bacterium produced many virus particles and they assembled into full viruses, the bacterium bursts and dies. This releases the produced viruses from the bacterium. The viruses now spread and infect other bacteria and the cycle begins again.

How bacteria fight off viruses

Each infected bacterium is a risk to the whole bacterial community. An infected bacterium produces many viruses that can infect many more bacteria in a community.

This is why, bacteria developed several ways to defend themselves against viruses. And many bacteria use different modes of defence against viral attacks.

So, what does a bacterium do to defend itself against viruses?

Preventing the virus from binding

The first line of defence against a viral intruder is to prevent a virus from binding to the coat of the bacterium.

A virus recognises and binds to a specific component on the coat of the bacterium. So, a bacterium can mutate this component and change it to prevent the virus from binding.

Another option is for the bacterium to produce biofilm. Biofilm is a slime that covers the bacterium and all its bacterial friends and protects them from harmful components like antibiotics, chemicals and viruses.

Sending out bacterial decoys

A really smart way of bacteria is to mislead viruses. Bacteria can produce bubbles from their coats that still contain the specific components that viruses bind to.

A virus can bind to these specific components and infect the bubbles. But the bubbles do not contain machines to produce viruses. Therefore, the bacterium does not get infected and will not produce any viruses.

Smart bacteria!

Destroying what is coming in

After a virus attached to a bacterium, the actual infection starts when a virus injects its genome into the bacterium. This can be DNA or RNA.

Some of our little bacterial friends developed smart devices to recognise any DNA or RNA that does not belong to the bacteria. When a bacterium “sees” viral DNA or RNA inside the cell, it activates huge destruction machineries. These work like scissors and cut viral DNA or RNA into tiny pieces to make them non-functional. Now, the bacterium will not even start producing viral components.

Many bacteria have different kinds of anti-viral scissors. And each one machinery recognises and cuts one specific piece of viral DNA or RNA.

The interesting thing is that bacteria use these scissors also to learn to fight new viruses. With the so-called CRISPR-Cas system, a bacterium learns to recognise new pieces of viral DNA or RNA when it first “sees” it. The next time the bacterium is infected with that same virus, it already knows how to fight it.

This is similar to how our body learns to fight a virus after we gave it a vaccine. We show our bodies what a certain virus looks like and it can develop the right weapons against it. The next time this virus attacks our body, we already have powerful weapons to fight the intruding virus.

Inhibiting the viral genome

If a virus was indeed successful and injected its DNA or RNA into a bacterium, some bacteria can still handle this. In this case, the bacterium produces specific molecules that bind to the viral DNA and prevent it from functioning properly.

This prevents the bacterium from producing viral components from the viral genome.

If nothing else works there is still one way out

Imagine, a virus was indeed lucky and managed to inject its DNA or RNA into a bacterium. And then imagine, the bacterium did not destroy the viral DNA or RNA and it produced viral components.

Now, the bacterium needs to prevent that these particles assemble into full viruses so that it does not kill the bacterium and spread into the surrounding.

In this case, bacteria have one last line of defence. And this defence mechanism is a truly altruistic weapon: Kill itself to protect the others.

Yes, an infected bacterium is prepared to sacrifice itself so that the whole community survives.

Just before virus particles assemble to full viruses, a bacterium can activate a suicidal mechanism. Like this, no full viruses will be released into the surrounding. No other bacteria will get infected with this virus. Everyone is safe.

Because bacterial suicide is such a drastic mechanism, bacteria only activate it after all other defence mechanisms failed.

Multiple lines of defence to protect the whole community

As you can see, bacteria developed several ways to protect themselves from viral attacks.

Don’t forget that also viruses mutate and can become resistant to any of these mechanisms. So it is a constant microscopic war between all the different microbial players.

Interestingly, not one bacterium has all the described mechanisms and is perfectly protected. But each bacterium has a few of these anti-viral weapons. Therefore, by working together, the whole bacterial community knows how to fight off most viruses. This teamwork can indeed protect the whole community.

How much we can learn from our microbial friends about how to fight off nasty viruses :)

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