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

Everything is connected and our lives depend more and more on technology and electrical devices.

All electronic materials that we use, are produced with lots of energy, harsh processing and/or toxic chemicals. Many electronic devices and batteries are considered disposable. But these are not recyclable or biodegradable and they are often filled with toxic materials. 

So, just as plastic waste is an environmental burden, all electronic waste is becoming an increasing problem for both the environment and our health.

But also for this problem, bacteria provide a green and sustainable solution: Microbial nanowires.

What are microbial nanowires?

Some bacteria can produce protein structures that work like electric cables. Researchers don’t fully understand the details yet. But somehow bacteria use these protein structures to send and receive electrons. Hence, they produce electricity.

And microbial nanowires don’t just substitute synthetic electric cables, they are also lasting. Bacteria-produced nanowires can withstand temperatures up to 100 °C, extreme pH conditions and protein-destroying chemicals. 

And they are green!

Most electronic components that we synthesise, consist of some sort of metal to conduct electricity. Yet, microbial nanowires do not contain such toxic metals and are thus considered harmless to the environment.

Which microbes produce green nanowires?

Many bacteria form cable-like structures that they send out of the cell. Researchers call these structures pili and they have different functions. For example, bacteria can use them to send or receive genetic material.

The bacterium Geobacter sulfurreducens produces this such a type of pilus, but with one difference: Its pilus can conduct electricity. This is why researchers call it an e-pili.

Other bacteria, like Shewanella oneidensis, produce nanowires that they produce from outer membrane vesicles. Outer membrane vesicles are blebs from the membrane of a bacterium. And in the membrane of the vesicles are electron transporters through which electrons hop. The vesicles then extend and eventually become a nanowire with the ability to conduct electricity.

Researchers even found archaea that produce so-called e-archaella. These work similarly to e-pili and help archaea to exchange electrons with their environment.

Why do bacteria produce microbial nanowires?

Researchers don’t fully understand why bacteria use nanowires to conduct electricity. But they are convinced that bacteria produce nanowires for food.

When bacteria produce the nanowires, they immediately transport them outside of the cell. They stay connected with the cable while the cable reaches out to new nutrient sources.

For example, bacteria can connect their nanowires with solid metal oxide particles. By transferring electrons to the metal oxides, they become soluble and the bacteria can use the metal for their metabolism. Like this, microbial nanowires function as arms for bacteria. They try to reach metals that are otherwise too far away from the bacterium.

Also, bacteria produce these nanowires in biofilms or cell aggregates. This looks as if bacteria form electrical networks to exchange electrons. However, it is not clear yet to researchers what the advantage of such a microbial electrical network is.

How can we use microbial nanowires?

Yes, electronics are meant to help us bring our thoughts and ideas to life in creative ways. So, maybe it is about time to use life for electronics as well. This is how e-biologics were born. 

Researchers learned under which conditions bacteria produce a lot of e-pili. They then cut them off the bacteria, dry them and fix them. These green microbial nanowires have even higher conductivities than when connected to bacteria. 

Therefore, microbial nanowires can be sustainable solutions to our increasing electronic waste problem. 

And what about degradation?

As often, when Nature knows how to produce something, it also knows how to destroy it. So, you could throw out your broken bacteria-produced electronic component onto the compost pile. And the bacteria would take care of them and degrade them.

Microbial nanowires are very robust and conduct electricity. Hence, they could be conducting components in electronic devices such as biosensors, light-emitting diodes and organic solar cells.

Researchers are also trying to increase the conductivity of microbial nanowires. For example, the bacterium Geobacter metallireducens produces a nanowire that conducts electricity 5,000 times better than the one from Geobacter sulfurreducens. By understanding the differences between these two structures, researchers can create nanowires with even higher conductivity.

Bacteria powered devices

We know that cable bacteria can conduct electricity over distances up to 7 cm Yet, microbial nanowires are even more remarkable. Usually, proteins are bad electron conductors. But again, bacteria created masterpieces by developing protein structures that are great electron conductors. 

Now it is up to researchers learning to handle e-pili to produce e-cables that one day we might use in our electrical devices.

And who knows maybe one day, we will have self-powering devices that contain bacterial biofilms producing their own electricity.

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

But as we know all this plastic is seriously hurting our planet, the animals on it, the plants and also ourselves. Not only plastic is incredibly stable and its breakdown products can be found almost everywhere, but producing plastics takes a massive toll.

Producing plastics hurts our planet

Making plastic materials is an energy-rich process that requires extracting and burning fossil fuels and petroleum. Chemicals from petroleum are extracted and combined into long chains called polymers.

However, petroleum and fossil fuels are resources that are limited. Plus, burning fossil fuels releases a lot of carbon dioxide, which leads to climate change and air pollution.

Currently, it is still easier and cheaper to make new plastics than recycling and reusing the already plastic items. Plastics are very durable, so it takes a lot of energy to break them down and melt them into a reusable form.

The idea is to find a greener and more sustainable way to make plastics.

Gladly, there is—bacterial-generated plastics!

Bio-plastics from bacteria

Many bacteria produce products that we use in our daily lives, from fermented foods like yoghurt, kombucha and beer to biofertilizers and ethanol that we use for biofuels. For example, the bacterium Escherichia coli, commonly known as E. coli, produces many medicines, like antibiotics and insulin used for diabetic treatment.

So, asking bacteria to make plastic isn’t that hard to believe.

How do bacteria make bio-plastics? 

Plastics are long chains of smaller units called plastic monomers. These monomers can look different, which finally make the different kinds of plastics.

When bacteria have too much energy inside their cells, they produce a lot of these monomers. They then link these monomers into polymers to store energy.

Interestingly, different bacteria can produce different kinds of monomers. And different combinations of these monomers make different plastic polymers.

When living organisms like bacteria or fungi produce plastics, these plastics are called bio-plastics.

For example, several microorganisms, such as Burkholderia xenovorans and Pseudomonas strains produce the polymer polyhydroxyalkanoate (PHA). In these cases, PHA serves to store carbon and energy during times of hunger.

You can understand PHA as fat in our bodies; the bacteria store energy and carbon for when they need the extra energy. But instead of viewing PHAs as fat, researchers are learning ways to use these polymers to create sustainable, biodegradable bio-plastics!

Engineering bacteria to produce bio-plastics

By learning how to use building blocks already made in nature, we can create plastics that are a lot healthier for the planet. But first, scientists need to make sure bacteria can produce enough bioplastic polymers to meet the worldwide demand.

To achieve this, even bacteria need some engineering help from scientists to produce more of the bio-plastics. Maybe engineering bacteria sounds scary, but it just means adding genetic material to a bacterial cell so that the cell knows how to produce the wanted product.

Genetic engineering is how E. coli makes insulin. And that same E. coli can also be engineered to make bio-based polymers.

One group even engineered E. coli to produce common plastic building blocks from the simple sugar glucose. Glucose is an abundant and renewable starting material, making bacterially produced plastics more sustainable than processes that rely on fossil fuels. Plus, this one-step process using E. coli is much simpler than the current way to make plastics.

But it is not just E. coli that scientists are trying to use to make bio-plastics. Researchers engineered both the bacteria Novosphingobium aromaticivorans and Ralstonia eutropha to produce biopolymer building blocks. However, we still need more research to optimize the process.

Benefits of bacterial bio-plastics

The plastics made by bacteria require less burning of fossil fuels, while many precursors used by bacteria are also sustainable. Both reducing non-renewable resources and instead using renewable resources makes bio-plastics a healthier and ‘greener’ option for the planet.

Additionally, some of the bio-plastics are more biodegradable than conventional plastics. Because these polymers are already natural products, other microorganisms and natural processes already know how to break them down and release natural products back into the environment.

Synthetic polymers found in traditional plastics are meant to last forever and can take decades to break down! This means that all the plastic trash fills up our landfills and oceans.

One study found that a bio-plastic item had a lower environmental impact as compared to a traditional plastic item over the item’s lifetime. That’s because the production of bio-plastics emits fewer greenhouse gases, uses fewer fossil fuels, and produces fewer toxins as compared to traditional plastic production.

In all these ways, bacterial bio-plastics are making the Earth greener.

A greener future with bacterial bio-plastics

Plastic pollution is a threat to our planet. These items overflow our landfills and oceans, where they sicken us and wildlife. In 2010 alone, it was estimated that up to 12.7 million metric tons of plastic ended up in the oceans! All this plastic hurts aquatic life and our planet’s marine ecosystems.

Luckily, scientists and engineers are exploring ways for bacteria to reduce our plastic pollution, both by creating bioplastics and degrading already produced plastics.

Using bacteria and bacterial enzymes, we can soon produce biodegradable plastics with less energy. From food to medicine to plastics, microbes are important for producing items we need to live.

However, even with microbes’ help, we can all play a part by reducing our plastic consumption, buying reusable over disposable products and recycling our plastics appropriately.

Along with microbes, we can save the planet!

Takeaway messages from this week’s article

• Plastic production is a major burden on the planet
• Bacteria can produce the building blocks for bio-plastics
• Bio-plastics start with sustainable precursors and are more environmentally friendly as compared to fossil fuel-derived plastics

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

Geosmin is one of these bacterial products that easily vaporise into the air and often have distinct smells. They are called volatile compounds.

Some other volatile compounds make the taste of chocolate or the smell of Cheddar cheese. And others, like geosmin, the smell of rain.

Bacteria produce geosmin – a volatile organic compound

Geosmin has this specific earthy or musty odour. It is the natural smell after a refreshing summer rain; the earthy smell of beets or carrots but also the off-tastes in water or wine.

You probably know what I am talking about.

Geosmin itself is not toxic, however, toxic fungi and bacteria produce geosmin. To our brain, the smell of geosmin signals that toxic fungi or bacteria are growing. So, our brain protects us from those by telling us not to eat the food. Thanks, brain!

Animals can also “smell” geosmin. For example, when the vinegar fly senses geosmin, it understands that toxic fungi are growing. In this situation, geosmin also acts as a repellent and the fly chooses not to eat or live around that place.

On the contrary, some mosquito species are attracted to the smell of geosmin. For them, the geosmin smell means that they are close to a lake, so the mosquito chooses to lay its eggs in the vicinity. Later, the mosquito larvae grow in that lake where they already have a food source. They will eat the bacteria. So, to mosquitoes, the geosmin smell is a sign of food.

Streptomyces – a geosmin producer

There are a few families of bacteria that produce geosmin. One of them is bacteria from the Streptomyces family. And Streptomyces already has a pretty interesting lifestyle.

Streptomyces not only grows as a bacterial cell, but it also produces very long and thin arms that grow out of the bacterial cell; so-called mycelia. The mycelia from one bacterium form a connected network with mycelia from other bacteria. And this complex mycelia network can extend into the soil, spread around soil particles and even wrap around tiny organisms.

After forming an interconnected mycelial network, the Streptomyces bacteria produce spores. And interestingly, Streptomyces produces these spores at the end of the mycelia arms.

Bacterial spores are non-viable versions of bacterial cells, just like a plant seed is a non-viable version of a plant. Spores generally only contain the genomic DNA of the bacterium, proteins to stabilise the DNA and proteins to react to the environment.

Similar to plant seeds, spores are wrapped in a thick envelope to protect the spore from the surrounding. Then, when the environmental conditions are better, the spore – just like the plant seed – germinates and forms a viable bacterial (plant) cell. This cell can then grow and metabolise and form new mycelia.

Why do Streptomyces bacteria produce geosmin?

Interestingly, when Streptomyces starts forming spores, the bacteria also produce geosmin.

Research found that a little insect-like animal, the springtail, is actually attracted to geosmin-producing bacteria. These tiny invertebrates – also known as snow flies or Collembola – live in the soil. And here, they are especially attracted to Streptomyces spores.

Researchers saw that the springtail uses its tiny antennae to smell the geosmin. The insect then follows the geosmin smell and once it found the Streptomyces spores, it starts eating them.

What is the advantage of being eaten by springtails?

Yes, it seems that bacteria produce geosmin to attract animals and insects to be eaten by them. To understand the reason for that we have to know that the springtail is covered with a waxy outer layer. Spores, on the other hand, have a hydrophobic envelope that easily sticks to the waxy springtail. This makes the spores stick to the springtail.

And when the animal moves around in the environment, it carries the spores around. So, it seems that bacteria use the animal as transport vehicle.

Also, the researchers saw that the springtails absolutely love eating those Streptomyces spores. They even found that the spores are not digested by the springtails. Instead, the springtails had viable spores in their faeces from which the bacteria could grow again. This finding gave the researchers another clue that Streptomyces spores might use the animals for transport.

So, it seems that Streptomyces bacteria produce geosmin to attract insect-like animals to attach to them and use them to hitchhike to different places. In a new place, there might be more nutrients for the spores to germinate, form viable bacteria, grow and reproduce.

From this, the cycle starts over again, as the bacteria form mycelial networks again to produce spores. Then, the bacteria produce geosmin to attract insects to get carried somewhere else again.

Bacteria live with many more players in the environment

Yet, one thing to take into account at this point:

Both Streptomyces and springtails live in the soil and in this study, the researchers only looked at how these two species interact with each other.

In the soil, there are several other bacteria, fungi, viruses, insects or tiny animals. So far, we have no idea about how any of these other organisms could impact the interaction between Streptomyces and springtails. The researchers did this study in the controlled environment of the lab. But the whole game might completely change in the wild environment of the soil.

However, I still think this is a cool example of how bacteria trick animals for their own good.

Take away from this article:

• Bacteria produce volatile compounds like geosmin that animals can taste or smell and be attracted to or repelled from
• Bacteria specifically produce geosmin to attract springtails to eat the bacterial spores
• Springtails transport the bacterial spores to new places

The post Bacteria produce geosmin to trick bugs into hitchhiking appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

If you are like me, you would make sure to always have your stock filled with this delicacy.

Especially in tough times, you need it more than ever. And you are trying to hide the chocolate from yourself. Yet, you would always find it again and indulge in its sweet-bitter taste that feels like home to you.

But did you know that chocolate, as well as other foods like beer and wine and bread, would not taste as we know it if it wasn’t for our little microbial friends?

That bacteria and microbes actually make the chocolate taste because they produce certain molecules that give it its flavour?

So, next time you enjoy your piece of chocolate, be grateful to bacteria and their superpowers for providing you with such a delicious fermentation product.

Where does chocolate come from?

It all starts with cocoa beans.

Cocoa beans are the seeds of the fruit pod of the tree Theobroma cacao that grows in tropical regions. These beans usually grow within the slimy white-creamy pulp inside the pod.

When the pods are ripe, people harvest and open them. They take out the beans and the pulp from the pod and leave them in the sun to ferment. This takes up to a week, during which the beans are regularly moved to avoid the growth of toxic fungi.

When the beans are dry, they are roasted to kill the remaining bacteria. This process is also important for the flavour of the beans. Then the beans are crushed into cocoa nibs and separated into cocoa powder and cocoa butter and processed into delicious chocolate.

Which bacteria are involved in cocoa fermentation?

When growing on the tree, the inner of the fruit pod is free of microbes. Only the surface of the pod is covered by different bacteria, yeasts and fungi. This consortium of microorganisms is the co-called COCOBIOTA.

When opening the pods, the microbes from the outside come in contact with the inner pulp where they start doing their magic. Without the microbial activity, the pulp is full of sucrose and citric acid and tastes very “sugary acidic and really good. Really unexpected.” as our graphical wizard, Noémie knows from her own experience.

Interestingly, cocoa fermentation is a naturally occurring process, so no artificial bacterial starter culture is added. Only those microbes that are present on the pod ferment the beans.

And scientists found that the superheroes of chocolate fermentation are lactic acid bacteria like Lactobacillus fermentum and Acetobacter pasteurianus and the yeasts Saccharomyces cerevisiae, Hanseniaspora thailandica, Hanseniaspora opuntiae and Pichia kudriavzevii. Also, many other microbes, that are still not well characterised, are involved in the process.

What happens during cocoa fermentation?

Since the inner pulp of the bean is so acidic, not many bacteria grow on it. However, yeasts and lactic acid bacteria love this kind of sour environment. So, they grow and metabolise the pulp.

First, yeast enzymes break down the sucrose of the pulp into the sugars glucose and fructose.

Next, different yeast strains metabolise the glucose and fructose and produce ethanol from the sugars. This is the actual fermentation process. In the next step, lactic acid bacteria make acetic acid and lactic acid from the ethanol.

Due to the metabolic activity of the microbes, the temperature of the pulp rises. Yeasts generally do not like this warmth and die.

Instead, other microbes break down the citric acid which makes the pulp less acidic. Now it is an environment that is very friendly for other bacteria so that bacteria like Bacillus, and fungi, as for example Penicillium citrinum and Aspergillus fumigatus start growing.

This consortium of microorganisms produces several compounds that diffuse into the cocoa beans. Without the bacterial activity, the raw beans “are definitely far from chocolate taste” as Noémie put it.

What chocolate-tasting molecules do bacteria produce during cocoa fermentation?

Scientists are just starting to understand the microbial network and metabolism that create the chocolate taste. You can understand the bacterial metabolism as the following phenomenon.

When bacteria live in an environment with an overload of nutrients (like within the pulp full of sugar), they switch their metabolism to high activity. In this mode, bacteria use their normal metabolism to grow and divide and be happy. On top of that, they have all that excess sugar with which they fill up the cell storage for bad times. And from these stored sugars, they produce additional fancy molecules, so-called secondary metabolites.

Imagine the sugars as your monthly salary. In normal times, you pay all your basic monthly bills, like rent, electricity etc, and probably put the rest in your savings. When you get a massive paycheck and swim in cash, you do all that as well, plus you buy some additional fancy stuff that you don’t really need to survive. This additional stuff represents those secondary metabolites.

Secondary metabolites are often super complex molecules and certain bacteria even produce unique compounds that no one else produces. For example, antibiotics are secondary metabolites as well and so are certain probiotics.

Bacteria produce the right mix for the chocolate taste

In the case of chocolate, the right composition of the secondary metabolites is important to give chocolate its unique taste.

For example, the bitter taste of chocolate comes from caffeine and theobromine. These compounds are especially important if you prefer chocolate with higher cocoa content as it contains more caffeine and less sugar.

Another group of secondary metabolites that microbes produce during cocoa fermentation is polyphenols. Polyphenols are also prebiotics so they are actually beneficial for our health. You can find other polyphenols also in some fruits, nuts, red wine and, obviously, chocolate.

In all, by producing the right mix of these secondary metabolites, bacteria and fungi change the taste of the cocoa bean into the delicious chocolate flavour that you are familiar with.

Thank bacteria for the delicious chocolate taste

And to make you feel better when enjoying your chocolate: Researchers found in animal and human studies that cocoa itself has health benefits. After eating cocoa, people showed lower rates of cardiovascular disease, diabetes and vasodilation which might even have positive impacts on learning and memory regions.

However, as always when it comes to diet, quantity is key ?

So, the next time you enjoy your chocolate, be grateful to bacteria and their chocolatey superpowers!

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

Yes, bubbles!

No, bacteria don’t just produce bubbles and try to hit another microbe with them. They are more sneaky. Bacteria fill these bubbles with antibiotics. And antibiotics are toxic and kill microbes.

So, when these toxic bubbles hit other bacteria, they will suffer.

Let’s look at where these bubbles come from and why bacteria decide to fill them with antibiotics.

Bacteria and their membrane(s)

Bacteria come in one of two kinds. They can have one or two cell membranes.

If a bacterium has one cell membrane, it is called Gram-positive. If it has two cell membranes, an inner and an outer membrane, it belongs to the Gram-negative bacteria. 

The outer and inner membranes of Gram-negative bacteria are slightly different. Interestingly, the inner membrane of Gram-negative bacteria is the same as the cell membrane of Gram-positive bacteria. But in Gram-positive bacteria, that membrane has a lot of additional stuff to make it thicker.

Because Gram-negative bacteria have two membranes, their outer membranes can form “blebs”. These blebs, also called vesicles, eventually form round spheres – or bubbles – and detach from the membrane which is how they are released into the environment.

Bacteria and their outer membrane bubbles

As you can see, these bubbles are made from the outer membrane of Gram-negative bacteria. This is why they are called outer membrane vesicles. These are basically a double layer of lipids in the form of a sphere with stuff inside. 

Within these bubbles, bacteria pack anything that they want to get rid of. This can be cell junk and can come from cell machines that don’t work anymore. Bacteria can get rid of that stuff by throwing it out.

About Chromobacterium violaceum

One bacterium that produces these outer membrane vesicles is Chromobacterium violaceum. And this one has a special reason to produce bubbles: it uses them to kill other bacteria.

Chromobacterium violaceum produces the antibiotic violacein. Violacein is a purple molecule and turns Chromobacterium colonies into purple dots. 

Since violacein is an antibiotic, it kills other bacteria. However, this antibiotic only kills Gram-positive bacteria, those with only one cell membrane.

The problem with violacein is, that it is a very hydrophobic molecule. This means that it is insoluble in water. Hence, researchers were interested to find out how Chromobacterium transports violacein through water to other bacteria. 

Chromobacterium violaceum bacteria produce toxic bubbles

So, researchers had a look at Chromobacterium cells. They saw that these bacteria produce bubbles from their outer membrane. And they do indeed look like spikey bubbles as in the picture below.

The researchers then purified the vesicles and added them to Staphylococcus aureus, a Gram-positive bacterium. The vesicles killed Staphylococcus aureus, hence the researchers thought that the violacein would be inside these vesicles.

Then they grew a Chromobacterium mutant that did not produce any violacein. But this mutant still produced outer membrane vesicles. Surprisingly, the vesicles from this mutant did not kill Staphylococcus aureus. 

From this, the researchers concluded that Chromobacterium transports the violacein within the bubbles.

This meant that the researchers found new functions for outer membrane vesicles. Hence, bacteria use them

a) to solubilise a hydrophobic molecule

b) to transport a hydrophobic and toxic molecule towards other bacteria

c) as bacterial weapons

Now, this concept gives researchers interesting possibilities to apply outer membrane vesicles.

Maybe, one day we will find a way to fill these bubbles with therapeutic molecules and send them towards tumour cells or we just found a new way to deliver antimicrobial substances in general.

For sure, scientists will come up with some cool new ideas to use outer membrane vesicles in the clinic, but as always, that requires a lot more research ?

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