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

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!

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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

How are they aware of their bacterial neighbours? 

They cannot see them or hear them. 

But do bacteria talk to other bacteria?

Yes, they do!

Like humans, bacteria talk to each other and socialize. But obviously, they cannot send messages or call each other. They have completely different communication channels that are not based on words.

So how do bacteria speak to other bacteria and even interact with them? 

They use special molecules. Researchers call these kinds of molecules extracellular signalling molecules. This means, bacteria produce these molecules and send them outside of the cell (extracellular). There, they can be a signal to other bacteria.

Microbiologists call this phenomenon quorum sensing. This means that a bacterium “senses” its “quorum”. A quorum means the number of other bacteria in the surrounding. Hence, with quorum sensing, a bacterium knows exactly how many other bacteria are nearby. 

The next step is then population-density dependent cell-to-cell communication. This fancy term means that only when enough bacteria are together (a high population), do they talk to each other (cell-to-cell communication).

But why is it important to bacteria to have all this bacterial chatting going on? Do they not like being lonely?

Why do bacteria need to talk to each other?

A community is always stronger than an individual. And the same is true for bacteria.

Many bacteria together can face the harshest environmental challenges. We also discuss the power of microbial communities when talking about multicellular organisms. 

But by using quorum sensing, bacterial cells are still individual cells. Yet, they act and react as a community; a real microbial community.

Bacteria have been using quorum sensing for millions of years. And it did shape evolution because bacteria learned to include others in their decision making. 

When bacteria face harsh conditions, they use quorum sensing to tell other bacteria in the surrounding that they are not alone. And as a community, they coordinate and tackle that challenging condition together. Therefore, bacteria developed mechanisms that respond to quorum sensing. 

For example, only when many bacteria live in the human body do they produce toxic virulence factors to make us sick. 

The same is true for biofilms. Bacteria only build their biofilm houses when they have other bacterial neighbours. 

On the contrary, a bacterium knows it is completely alone because no quorum sensing is happening. And when the bacterium also has no food, it might decide to sporulate. With this, the lonely bacterium assures to survive on its own until better times come.

Yes, quorum sensing controls a lot in the bacterial life, so how does this important mechanism actually work?

How does quorum sensing work? 

It all starts with one bacterium. 

One bacterium that produces these special quorum-sensing molecules. Researchers call these molecules autoinducers. And the bacterium sends these autoinducers out into the environment. We call this bacterium the sender.

Now, when another bacterium from the same family is nearby, it can recognize the autoinducer. This bacterium is the recipient. Both bacteria have specific receptors on its surface to which the autoinducer binds. 

Next, the recipient takes up the autoinducer. Inside the bacterial cell, the autoinducer can regulate genes. But only, when the amount of autoinducer inside the bacterium is high. 

Hence, when one bacterium sends out autoinducers, the recipient can only take up a few autoinducers. And these few molecules are not doing much on their own.

But now imagine, there are a hundred bacterial cells around. And each of them produces a few autoinducer molecules. Now, all recipient bacteria take up a lot of autoinducers. And a lot of autoinducers inside a bacterial cell start controlling genes. 

All these autoinducers can trigger the bacterium to produce nasty virulence factors or biofilm.

Therefore, with many bacteria around, they produce a lot of autoinducers and more bacteria take them up. Thus, more bacteria listen to each other. And then they produce more autoinducers and send them to the surrounding. Like this, they start chatting and making decisions together.

But what if the chatting bacteria are from different families? Do they still understand each other?

Is quorum sensing a microbial language? 

Researchers found that many bacteria use autoinducers to communicate with each other. And they also found that not all bacteria use the same autoinducer to communicate. 

It is like speaking different languages. 

And interestingly, some bacteria only produce one autoinducer. This is as if they only say one word. All the time.

And other bacteria produce several different autoinducers. So they speak several different words.

Imagine in a mixed microbial community. Different microbes produce hundreds of different autoinducers and send them to the environment. This means hundreds of different words spoken. Therefore, hundreds of different conversations and as such, a lot of chatting going on. 

But all these conversations are not always friendly. In some bacteria, quorum sensing also controls killer weapons. As soon as bacteria “hear” via the quorum sensing channel that other bacteria are around, they turn into fighters to kill the neighbour bacteria. 

As such, quorum sensing as a microbial language can lead to cooperation or competition between bacteria. And bacteria always try to adapt to new conditions. Therefore, by listening and responding to other bacteria, they developed new mechanisms. This is why quorum sensing played such an important role throughout evolution.

Where can we see bacteria talking in real life?

Scientists can see quorum sensing in the lab all the time. Often they grow bacteria in liquid in a glass flask. At the beginning, the bacteria are not many, so nothing happens.

After a while, bacteria grow in the flask and become a lot more cells and they do quorum sensing. And many bacteria start to produce colourful molecules as a response of quorum sensing.

For example, the bacterium Vibrio fischeri starts producing bioluminescence. Hence, the liquid with the bacteria starts to glow.

And these bacteria also use bioluminescence in nature. The Vibrio fischeri bacteria usually live inside the so-called light organ of the bobtail squid.

And at night, the bacteria grow and divide and do quorum sensing inside the squid. After a while, the bacteria start producing bioluminescence and the squid shines light towards the seafloor. Like this, it looks as if the squid is not present as it does not throw a shadow anymore.

With this mechanism, bacteria help the squid to survive at night. And all this through quorum sensing.

Quorum sensing – a fascinating language

Did we just convince you once again how amazing bacteria are?

Do you also think that quorum sensing is a fascinating language?

And is it not remarkable how bacteria can talk to each other and help each other?

So, yes, we think so. With this amazing mechanism, bacteria know they are not alone. And they can launch an appropriate response to an incoming signal. Just as you say “yes?” when someone calls your name. 

However, bacteria have their own language. And we are still learning to understand it.

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

They don’t have eyes to see what is going on.

Neither do they have ears to hear a foe approaching.

And yet they seem to know exactly what is happening around them.

How is that possible?

In other articles, we already looked at different mechanisms of how bacteria sense their environment. And we learned about various ways bacteria use to know what is going on around them.

Here, we will look at another one of these mechanisms. A mechanism in which bacteria destroy proteins to understand the environment and adapt to it.

But before we can look at why bacteria destroy proteins, we first need to understand how bacteria produce proteins.

Bacteria need proteins to produce proteins

Every living cell, like a bacterial cell or a human cell, contains DNA. And the DNA contains many different sections, which are genes. These genes are the templates for ALL proteins that a cell can produce.

A cellular machine called the polymerase (bright blue in the figure below) recognizes the start of a gene (yellow), before it transcribes this gene into a string of mRNA (grey). Next, a ribosome reads the mRNA fragment and translates it into a protein (yellow).

This is how every living cell produces proteins from DNA.

Now, we will focus on the first step: when the polymerase recognizes the start of a gene.

Bacteria need proteins to regulate protein production

When you think about it, bacteria do not always need all genes and all proteins. Just as you don’t need an umbrella when it is sunny outside, but it is always good to keep it handy. Similarly, bacteria have heaps of genes on that long string of DNA and they need some of them only under certain circumstances.

For this, all living cells have regulators. These regulators make sure that the polymerase only produces mRNA from genes that are required at a specific time point.

And these regulators come in two forms: activators and repressors.

Activators activate genes

Sometimes, the polymerase cannot recognize a specific gene on its own. This is when the polymerase needs an activator (green). 

An activator is a protein that binds to a specific gene only when needed. This attracts the polymerase to this gene so that it produces mRNA from that gene. Like that, an activator ensures that bacteria only produce certain proteins when needed.

This means something else needs to activate the activator at a specific time point. And while some activators are activated by specific systems as explained in How bacteria sense their environment, sometimes protein-destroying systems are involved. More about that below.

Repressors deactivate genes

Repressors (dark blue) do exactly the opposite of activators. These proteins bind specific genes right at the start. This blocks the polymerase from binding the start of that gene and from producing mRNA.

But when the bacterium needs a specific protein, the polymerase has to recognize and bind that specific gene. At that point, the bacterium has to get rid of the repressor.

So, let’s have a look at how bacteria gain access to genes that need activators or are blocked by repressors.

Bacteria destroy proteins to understand the environment

The environment constantly changes for a bacterium. So, all the time, a bacterium needs to produce certain proteins to handle these new situations. Just as you take your umbrella when it is raining suddenly.

This is when the bacterium needs the polymerase to recognize a specific gene to make mRNA from it.

To get rid of a repressor or to activate an activator when needed, bacteria came up with a simple mechanism: protein destruction.

Yes, to produce proteins, sometimes bacteria destroy proteins.

Proteins that destroy proteins are called proteases and these work like molecular scissors. Proteases cut proteins in at least one specific location. This makes the protein fall apart and become kaput. 

When do bacteria destroy proteins?

Different bacteria developed various mechanisms when to destroy specific proteins. And researchers start to understand more and more about this way of regulation.

So, let’s have a look at a few cool examples of bacteria destroying proteins.

Radiation leads to protein destruction and survival

For example, the fascinating bacterium Deinococcus deserti has genes to cope with radiation and desiccation. However, the bacterium does not need to produce these proteins when there is no radiation or desiccation.

Under these circumstances, the repressor D (dark blue in the figure below) blocks these genes and makes sure the polymerase cannot recognize them.

But as soon as the bacterium is hit with radiation (lightning), the radiation activates the protease M (red). This protease can now bind the repressor D and destroy it. Now, that the repressor does not block the radiation genes anymore, the polymerase can recognize the genes and produce mRNA from them. Now, the ribosome produces proteins (yellow) that cope with the radiation. 

And this is how the bacterium Deinococcus deserti destroys proteins to survive. And yes, this bacterium has the superpowers to withstand radiation and desiccation like no other bacterium.

Antibiotics lead to protein destruction and resistance

In another example, Staphylococcus aureus has a similar mechanism to cope with antibiotics and become resistant. 

In the membrane of this bacterium sits the protease R (red) that is generally inactive. However, when the bacterium meets antibiotics (green molecules), the antibiotics change R. 

Now, the protease falls into the inside of the bacterium and destroys its target protein. This is the repressor I (dark blue), which sits and blocks a certain gene. After protease R destroyed repressor I, this gene is unblocked and the bacterium produces a protein (yellow) that cleaves the antibiotic. 

And this is how Staphylococcus aureus becomes resistant to antibiotics by destroying proteins.

Heat leads to protein destruction and survival

But bacteria do not only destroy repressors. They also use a similar mechanism to activate their activators. 

Generally, to keep an activator inactive, another protein is involved. This is the so-called anti-activator since it captures the activator and inhibits it from functioning. So, for the activator to become active and to bind its specific gene, the anti-activator needs to go. And this is exactly what bacteria do.

For example, in the soil bacterium Bacillus subtilis, the anti-activator Y (dark blue) captures the activator S (green). Plus, Y brings S to the cellular garbage machine (purple) to destroy this protein.

However, as soon as it is getting too hot for the bacterium, Y becomes unstable. So unstable, that it cannot hold S anymore. This means S gets freed, binds its favorite genes and leads the polymerase to them. Now, the bacterium produces proteins (yellow) that help the bacterium to cope with the damage from the heat.

And this is how Bacillus subtilis destroys proteins to cope with heat.

Destroying proteins means bacteria can survive

Here we explored three different ways of how bacteria destroy proteins for their own benefit. Interestingly, the benefit always handles the incoming signal which is often a sign of stress.

Like in Deinococcus deserti, radiation activates protein destruction that leads to protein production. And these new proteins now handle the damage after the radiation attack.

Or in Staphylococcus aureus; antibiotics activate a specific protease that destroys a repressor. Now, the produced proteins are meant to destroy the harmful antibiotics.

So by closing these circles, bacteria found efficient ways of how to read their environment and adapt to it.

Interestingly, most bacteria seem to use similar mechanisms. This means, the better we understand the way most bacteria work, the better chances we have to fight the nasty ones. So we need to keep researching the good bacteria, to understand the bad guys too!

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

Read on to learn what this fascinating superpower is and why magnetotactic bacteria work like a compass.

What are magnetotactic bacteria?

So-called magnetotactic bacteria are those bacteria that sense magnetic field lines and align with them. They then decide whether they swim toward the North or the South.

To actively swim through water, magnetotactic bacteria, like many other bacteria, have flagella. And they can have one flagellum on one side or one on each side or a bundle of flagella.

So far, researchers found magnetotactic bacteria on the whole planet and they mostly live in water sediments and oceans. Some magnetotactic bacteria even live in extreme spots like the hot springs in northern Nevada. Here, they grow happily at about 55 °C. 

Researchers gave these fascinating bacteria names that already let you guess their superpowers: Magnetospirillum magnetotacticum, Magnetospirillum magneticum, Magnetospirillum gryphiswaldense, Magnetococcus marinus or Desulfovibrio magneticus. And obviously, scientists keep discovering new species that can sense magnetic field lines.

Okay, now we know what magnetotactic bacteria are. Let’s look at what gives magnetotactic bacteria their superpowers to read magnetic field lines.

What are magnetosomes?

Magnetotactic bacteria can sense magnetic field lines because they have so-called magnetosomes.

Magnetosomes are tiny crystals of iron oxide or iron sulfide. And these crystals are surrounded by a lipid membrane within a so-called organelle. Magnetosome organelles lie within the bacterium and import and export iron from the bacterial cytosol.

These magnetosomes can have different shapes and sizes. Some crystals are cuboctahedral, prismal-shaped or even bullet-shaped. Like the super cool magnetosomes in the pictures below.

As you can see in the pictures, bacteria do not only have one magnetosome but several. And these magnetosomes can align in a perfectly straight line or cluster together on one side of the bacterium.

For a magnetosome chain or cluster to work, bacteria need to keep their shapes perfectly. For this, magnetotactic bacteria use so-called scaffold proteins. These scaffold proteins position the magnetosome within the bacterium and hold this chain in its place.

How do magnetotactic bacteria grow magnetosomes?

Because magnetosomes are made of iron, magnetotactic bacteria have very special iron uptake systems. These iron importers help the bacteria get as much iron into the cell as possible.

Then the bacterium needs to transport the iron toward the magnetosome. The problem is that free iron is actually toxic to the cell.

Hence, the bacterium needs to assure the iron does not come into contact with the cell content. Therefore, magnetotactic bacteria produce iron transporters that shield the iron from the surrounding. 

Now, the bacterium needs to carefully crystallise the iron to grow the magnetosome. This process is actually not well understood yet and researchers are on it to shed light on it.

Okay, now we know what magnetosomes are and how they are formed. Let’s look at how magnetosomes help bacteria sense the Earth’s magnetic field.

How do magnetotactic bacteria sense magnetic field lines?

Because magnetosomes are highly-concentrated iron crystals, they have a magnetic dipole. And since a bacterium has many magnetosomes aligned in a straight line, the magnetic dipole is increased.

So, the magnetosome chain works similarly to a compass needle and aligns along magnetic field lines. Just as a compass needle aligns with magnetic field lines and you align your position according to the compass needle.

And we have the scaffolding proteins that keep the magnetosome chains in place within the bacterium. Because of them, the whole bacterium aligns with the magnetosomes. So, when you think about it; the bacterium aligns with the magnetic field lines in a passive way.

Imagine you put a worm on a compass needle that it can’t move away from. The compass needle will always point North and thus the worm will always point North as well. So, no matter where the compass goes or how fast you turn yourself with that compass, the needle and the worm will always face north. But the worm is only aligning North passively. Same as the bacterium.

As we said at the beginning, magnetotactic bacteria always have a flagellum that helps them swim around. Similar to other motile bacteria, a bacterium swims because it rotates its flagellum. This moves the bacterium forward or backward.

But since the magnetotactic bacterium is aligned to the North or South, it will only swim toward the North or South.

And researchers found that magnetotactic bacteria can be either North-bound or South-seeking. Hence, depending on whether the bacterium lives in the northern or southern hemisphere, it will swim towards the North- or the South pole.

So, next time you want to hitchhike on a magnetotactic bacterium, ask it first where it is going!

Why do magnetotactic bacteria sense magnetic field lines?

Researchers do not have a clear answer to this one yet.

One hypothesis is that within the depth of the water, a bacterium has three dimensions to align to, swim to and explore. By aligning the bacterium to the Earth’s magnetic field, the bacterium only moves in one dimension. This makes the search for the perfect location easier. Otherwise, bacteria might swim aimlessly in all three dimensions and get lost.

Also, most magnetotactic bacteria are chemotactic and even aerotactic. This means they move towards oxygen – again to find the perfect spot to live and to find nutrients.

And some magnetotactic bacteria are even phototactic and swim away from blue light. Researchers think that because blue wavelengths are a sign of deep water, bacteria are trying to avoid going too deep. But this still needs some more research.

Do magnetotactic bacteria help other organisms?

Researchers found an amazing example of a symbiotic relationship in the microbial world.

They discovered magnetotactic bacteria that live on a eukaryotic protist. The two species exchange metabolic molecules, so they feed each other.

What I find really fascinating is that these two species together become a swimming magnetic superorganism. The researchers saw that the magnetotactic bacteria completely cover the surface of the protist. And because the magnetotactic bacteria have magnetosomes, they align with the magnetic field. Thus, the entirety of bacteria on the protist aligns the whole protist with the magnetic field. 

Interestingly, this species of magnetotactic bacteria lost their flagella during evolution. So they are unable to swim. But the protist still has a swimming rotor. Thus, because of the symbiosis, this multi-organism is able to sense and swim along the magnetic field lines. 

Magnetotaxis – a bacterial superpower

Okay, I hope I could convince you yet again how amazing bacteria are and that they do have superpowers.

Again, it is not a hundred percent clear yet, how sensing magnetic field lines help bacteria to survive. But as usual with evolution, if some species kept such an impressive superpower, it must have a big advantage. 

We just don’t understand it yet.

The post How bacteria read and follow the Earth’s magnetic field appeared first on Bacterialworld.
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

When you look at a bacterium, you see that it has no eyes to see, no ears to hear and no nose to smell. So, how do bacteria know where they are and what is happening around them?

Bacteria use some simple but highly efficient systems to make sense of their environment. Here, we will look at two of these systems.

Bacteria use complex systems to sense their environment

When we talk of the environment of a bacterium, we mean any kind of condition that a bacterium might encounter in its daily life. This includes temperature, pH, presence or absence of a nutrient, oxygen levels or the presence of certain antibiotics…

And bacteria need to know about the state of these conditions. They need to know how warm or cold it is, where the food is or if they are close to deadly antibiotics. Once they sensed this condition as a so-called signal, they need to respond to it.

This is why scientists called these systems response regulator systems. Bacteria use them to regulate their response to a specific signal.

The one-component system

The simplest of these systems is the ‘one component system‘ as this includes only one protein. This protein has two parts, or modules. One module is the sensor module (bright green in the picture below) which senses or measures a certain signal within the cell. The second module is the response module (dark green) which responds in a specific way to the measured signal. 

The two modules are in close contact with each other. Thus, the response module knows exactly what the sensory module measures and how it is supposed to react. 

In most cases, the sensory module measures the presence or absence of a certain molecule, for example, oxygen or iron. This happens because the sensory module has a very high binding affinity for this molecule.

For example, if oxygen is present within the bacterial cell, it binds to the sensory module. When oxygen is not bound to the sensory module, it has a slightly different structure. In this case, the response module reacts by binding to another response module of another one-component system.

Now, this double protein can bind to bacterial DNA at specific positions. It binds right next to a certain gene to turn this gene on so it can produce specific proteins. These proteins will now help the cell deal with the lack of oxygen.

Like this, the response module ensures that the cell gets the right set of proteins that are needed in this specific situation.

Okay, but this system only measures conditions within the cell. How does a bacterium know what is going on on the outside? 

The two-component system

In this case, the sensory module and the response module are located within two separate proteins. These are the sensor protein and the response protein. Since two proteins are involved in this system, scientists call it the ‘two-component system‘.

Here, the sensor protein has two parts or modules and sits in the bacterial cell membrane. The sensor module is similar to the module in the ‘one-component system’ that we discussed above. The second module has an enzymatic activity (orange in the figure below).

The response protein also has two modules and lives inside the bacterial cell. The receiver module (red) waits for specific interactions with the sensor protein. Interestingly, the second module, the response module, is the same as in the ‘one-component systems’. 

Two-component systems sense signals in the environment

Because the sensor module sits in the bacterial cell membrane, it can sense signals inside or close to the membrane. For example, certain antibiotics damage the cell membrane. Bacteria measure or sense such membrane damage with specific sensory modules. 

Other sensory modules can measure the temperature within a bacterium. The membranes of bacteria are made of fatty acids and you know how the consistency of fat changes when the temperature changes? Similarly, with rising temperatures, the membrane becomes more fluid. On the contrary, at low temperatures, it is more rigid. Interestingly, sensory modules act like thermometers and measure the fluidity of the cell membrane. 

Once a certain signal activates the sensor module in the membrane, its enzymatic module also gets activated. The enzymatic module can then interact with the receiver module from the response protein and adds a little molecule (P) to the receiver.

This addition changes the structure of the response protein. Now, the response module can bind to another response module, similar to what happens in the ‘one-component system’.

Hence, the response itself is similar. Bacteria produce proteins that cope with the detected signal. One example is dealing with changing temperature or getting rid of antibiotics.

The two-component system is also part of the chemotaxis system which controls the movement of bacteria towards nutrients.

Bacteria know how to adapt to the changing environment

In all, bacteria found amazingly simple but efficient ways to sense and know what is going on in their environment. Using these systems, they know exactly how to deal with the changes based on the information they receive. This simple trait, in my opinion, makes them super smart.

Takeaway message from this article 

• Bacteria sense their environment and couple it directly to a specific response
• Signals can derive from within the bacterium or outside of the cell
• The response helps the bacterium to adapt to the new environmental conditions 

The post How bacteria sense and respond to the environment appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

And this process is very interesting to researchers. It tells them how bacteria move in the environment, advance their populations and evolve in general. So, here we explain one mechanism of how bacteria break biofilms.

The bacterium Desulfovibrius vulgaris likes water pipes

As you might know, bacteria are basically everywhere. And they like to build their biofilm houses on pretty much any surface they can find. Be it in or on our bodies or somewhere in nature and the environment.

For example, the bacterium Desulfovibrio vulgaris likes to live on metallic surfaces in the soil. These could be water systems or pipelines that are wet and warm.

Here, the bacterium builds its biofilm house to be protected from the surrounding. Now, Desulfovibrio vulgaris can use the metal from the pipe to gain energy, so it “breathes” the metal. But this metabolic activity leads to the metal pipes corroding or rusting.

And when these metal pipes start corroding, they stop functioning properly which can lead to some serious health issues. So, researchers decided to look into how these bacteria build and break their biofilms.

Bacteria build and break biofilms

The researchers looked at the genes of Desulfovibrio vulgaris with bioinformatic tools. And they found some genes that the bacterium uses to produce less biofilm. Researchers already know some of these genes from other bacteria. Here, these genes also prevented the bacteria from producing a lot of biofilm.

So, the researchers decided on one of these genes and looked at them in more detail. They found that the gene produced a specific enzyme, which is a protein with a special activity.

And in this case, the enzyme’s activity was that it works like a scissor and breaks the biofilms of Desulfovibrio vulgaris. But the researchers also found that this scissor can break the biofilms of other bacteria.

Scientists have always tried to find some kinds of scissors in bacteria that can break biofilms. However, they usually focused on biofilms formed by bacteria in hospital settings. Now, they finally found a new pair of such scissors made by bacteria that live in the environment.

Why do bacteria produce scissors?

Do they not like living in their biofilm houses?

To answer this question, we need to understand that the bacterial biofilm lifestyle works as a cycle. Bacteria build biofilms and use them as houses. As soon as nutrients are scarce or there are too many bacteria within a biofilm, some bacteria break the biofilms to cut themselves loose.

For this, bacteria need to break down parts of their biofilm houses for which they use their special scissors. After cutting themselves free from the biofilm, they start swimming and looking for a new place to live. Once they found it, they will settle down and build a new biofilm house.

By discovering these new kinds of scissors, scientists now have novel tools to combat bacterial biofilms. These tools could inhibit bacterial biofilms in many different settings like the environment or in hospitals.

The post Bacteria breaking free from home appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Yes, you read correctly.

So-called cable bacteria transport electrons from cell to cell over centimetre-long distances and thus conduct electricity.

Mind-blowing.

It all started when in 2001, researchers measured electric currents in aquatic sediments. Soon afterwards, they found that this current is due to specific bacteria that exchange electrons with the surrounding.

And they called these bacteria cable bacteria.

So, let’s look at these fascinating species in more detail.

What are cable bacteria?

Cable bacteria are multicellular bacterial organisms meaning many bacteria from the same family are living very closely together. They usually share the same food and nutrients and help each other out. This tightness makes the whole bacterial community stronger and often gives them new superpowers – like in this case, the multicellular cable bacteria can conduct electricity.

Until now, researchers do not know much about cable bacteria, as they usually live in marine, freshwater and salt-marsh sediments. Here, they often use unusual components like sulfur or sulfur complexes to gain energy and grow. Such conditions are pretty difficult to imitate. So currently, researchers are struggling to grow them in a lab.

However, recent studies managed to find out what cable bacteria look like and how cable bacteria conduct electricity.

What do cable bacteria look like? 

For this, researchers took water samples from different locations. They then visualised the cable bacteria with different spectroscopic techniques. With these machines, researchers can magnify the tiniest things and get high-resolution pictures of bacterial cells.

Within these pictures, they actually saw that one “cable bacterium” is a multi-cellular microorganism. In the pictures below, you can see long chains or cables. Interestingly, these are completely surrounded by isolating walls. And within these cables, you can see single compartments, which are the bacterial cells.

These cables or chains, researchers call filaments and they can get up to 7 cm long.

What are cable bacteria made of?

Researchers are still trying to classify the family of cable bacteria. However, they know so far that cable bacteria are rod-shaped Gram-negative bacteria. This means these bacteria have an inner and an outer membrane as a surrounding and protecting wall.

Generally, between the inner and outer membrane is a liquid space that is the periplasm. This space kind of works as a flexible and soft buffer zone between the two membranes.

However, in cable bacteria, one bacterial cell is surrounded by an inner membrane to protect its cellular content. Then these cells arrange into a chain and share one common liquid periplasm. Next, one common outer membrane surrounds and stabilizes this bacterial-cell-periplasm chain. So, one outer membrane isolates the whole bacterial chain from the outside.

The whole chain is further held together by so-called fibres. You can see these fibres as those long dark grey lines in the pictures above. These fibres go along the cells through the whole periplasm of the cable filament. Researchers think, that these fibres give the cable its structure, stabilise the cable and protect it from breaking. 

As you can see, this whole structure indeed looks like a cable and insulate the bacteria on the inside from the outside. That’s pretty much where these bacteria got their name from. 

How do cable bacteria transport electrons and conduct electricity?

And why would they even create an electric current?

The short answer is to survive. As always, all organisms just want and need to survive.

So, let’s look at this in more detail.

Cable bacteria live in water sediments. These waters are full of oxygen in the top layers close to the surface. And they are full of sulfur in the deeper layers.

And cable bacteria use this oxygen-sulfur gradient to conduct electricity.

Cable bacteria now actually sense the oxygen in the water and align perpendicular to the waterfront. This means one end of the cable is in the oxygen-rich area at the top and the other end in the sulfur-rich area towards the bottom. Similar to the model below.

Bacteria breathe sulfur and conduct electricity

Now the filament works as a half-cell.

The bacteria in the deeper layers “breathe” the sulfur. This produces electrons (e^–) and protons (H⁺) as an anodic half-reaction. These electrons then travel along the cable within the liquid periplasm to the upper part of the cable. Here, the bacteria consume these electrons to reduce oxygen in a cathodic half-reaction.

These oxidation and reduction processes are part of each cell’s metabolism. So, this is what keeps every cell alive.

However, usually, both reactions happen within the same cell so that one cell gains energy from both reactions at the same time. Interestingly, cable bacteria found a way to uncouple the oxidation and reduction reactions.

Hence, oxidation and reduction mechanisms happen in different cells – one reaction in cells at the bottom of the cable, the other reaction in cells at the top of the cable. Yet, they somehow learned to do both reactions within one system – the cable. And this is the mind-blowing part.

What does it mean for the environment?

This unusual metabolism of cable bacteria has some interesting effects on their surroundings. These reactions produce protons in the deeper water layer and reduce them in the surface layer. This leads to a drop in pH in the deeper layer and an increase in the pH near the surface. This can mineralise and demineralise metal complexes. 

Researchers suggest that these (de-)mineralisation processes also have an impact on the geochemistry within the local environment in the water. However, how exactly the metabolism of cable bacteria influences the environment and maybe other species is still not well understood.

Since researchers only recently discovered cable bacteria, it is understandable that there are still many questions unanswered. But I am convinced that we will hear many more interesting facts about them and who knows, maybe one day bacteria will fuel some kind of seawater-based batteries…

Takeaway from this week’s articles:

• cable bacteria are filaments of a multitude of bacterial cells
• they can produce and consume electrons and transport them from one end to the other
• this electric current shapes the local environment in water sediments

The post Cable bacteria – unusual bacteria conduct electricity appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world