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

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

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

What are extremophiles

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

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

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

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

Extremophiles living in the deep sea

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

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

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

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

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

How extremophiles adapt to the deep sea

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

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

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

Extremophile bacteria have different membranes

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

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

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

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

What we can learn from extremophiles in the deep sea

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

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

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

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

The post Even at the dark and cold bottom of the sea, microbes flourish appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Do bacteria always only live in one form; either they are single cells or multicellular?

How do we distinguish between unicellular and multicellular bacteria?

Which advantage do bacteria gain from sticking together and forming multicellular organisms?

What are some examples of multicellular bacteria?

In this article, we will answer exactly these questions!

Let’s dig in!

What makes multicellular bacteria?

Scientists define multicellularity as a form of “biological organisation in which a permanent cell aggregate exhibits an activity more complex than that of the individual cells“.

This means that multicellular bacteria are only present in their multicellular forms. True multicellular organisms cannot go back being single-celled.

Hence, bacterial biofilms are no true multicellular organisms. Bacteria can decide between these two lifestyles; they actively produce the biofilm when needed and they break it off and become single cells again.

Also, a bacterial colony in a petri dish is not a multicellular organism. In a colony, a bunch of bacterial cells grow on top of each other. But the cells in the colony are not organised and they do not function in an organised manner.

Multicellular bacteria are organised

The difference here lies in the term biological organisation. Multicellular bacteria are organised due to two different concepts:

They work in an organised manner; bacteria within the multicellular organism need to communicate with each other. Thanks to communication, every bacterium within the organism knows what is going on, so it can react in an organised manner.

Just as when your stomach is empty, it tells your brain that you’re hungry and you react accordingly by eating. Your stomach and your brain are communicating with each other.

The second way to organise multicellular bacteria is by using different functions to advance the whole organism. Within a multicellular organism, some bacteria undergo a process called cell differentiation. Cell differentiation is what makes a human stem cell develop into a skin cell or a blood cell. And this skin or blood cell has more specialised functions than the stem cell that it was before.

The same can happen in multicellular bacteria. Some bacteria develop into specialised cells. These specialised bacterial cells have functions that other cells (or the single version of the bacteria) do not have.

Now, some of the bacteria have additional functions or abilities. And thus, the whole multicellular organism gains new bacterial superpowers that can advance the organism.

Why do bacteria form multicellular organisms?

Here, evolution plays a massive role since multicellularity has so many advantages.

In multicellular organisms, the labour is divided. Just as it is easier for you and your co-workers to work in a team with everyone doing what they are best at. With bacterial cells taking on new functions through cell differentiation, the whole organism profits.

Another advantage is that when bacteria cluster together, they can protect their core. And some multicellular bacteria keep their spores within the core for protection. Like this, their most vulnerable members are protected.

Also, multicellular bacteria are generally bigger than single bacterial cells. This makes it more difficult for attackers to prey on this organism. And we know how much bacterial warfare is going on in the microbial world.

What are some cool examples of multicellular bacteria?

Researchers have not found that many yet. But those multicellular bacteria, that they started to investigate, are pretty cool.

Well, that’s what I think, but see for yourselves.

Multicellularity in chains: filamentous cyanobacteria

Filamentous cyanobacteria are Earth’s oldest multicellular organisms. And thanks to them, we have all this precious oxygen on our planet.

Some cyanobacteria form long chains, so-called filaments. In such an organisation, the whole chain of cyanobacteria is surrounded by one common outer membrane. This means, that all cyanobacteria cells within the filament share one periplasm. And they use this periplasm to communicate with each other and exchange nutrients.

Also, filamentous cyanobacteria like the Anabaena species can undergo cell differentiation. In the picture above, you can see a chain of Anabaena cells. Some cells are smaller, which are the undifferentiated cells, and some are bigger blobs.

The normal-sized cells have photosystems and they perform photosynthesis to produce oxygen.

But when cyanobacteria do not have enough nitrogen, they start to differentiate into those bigger cells, so-called heterocysts. And these heterocysts are now able to fix nitrogen. This helps the organism with its nitrogen limitation.

The reason why Anabaena needs these two cell types is because the chemical processes of oxygen production and nitrogen fixation interfere with each other. They can not happen within one cell, which is why cyanobacteria need to have a different cell type for each process.

In the end, the cells share the produced oxygen and the fixed nitrogen with the whole filament. So everyone is happy with this arrangement.

Multicellular bacteria as electricity producers: cable bacteria

Cable bacteria form – similarly to cyanobacteria – long filaments that are surrounded by one common outer membrane. And they use this arrangement to transport electrons and conduct electricity.

We talked about multicellular cable bacteria in detail in the article Cable bacteria – unusual microbes conducting electricity. Head there to read about this special kind of multicellular bacteria.

Multicellular organisms in cell aggregates: Myxobacteria

Some bacteria, like the well-characterised Myxobacteria, can form huge cell aggregates of up to 100’000 cells. These cell aggregates are called fruiting bodies and their main function is to feed and transport their spores.

The spores have a special place within the Myxococcus fruiting body: They are kept at the core of the fruiting body. Here, they are safe and protected from the surrounding.

Interestingly, myxobacteria are also known as wolf-pack predators, because of the way they attack their preys. They kill their preys by launching a massive attack and secreting lethal bacterial toxins. This kills the prey instantly and the whole fruiting body can feed on the prey.

Multicellular organisms forming hyphae networks: Streptomyces bacteria

Streptomyces bacteria develop a complex network of hyphae within the soil. With this network, Streptomyces bacteria can branch into different directions and elongate the branch tips.

Within the branches, some hyphae within the soil have secluded compartments with walls to separate them from the rest of the network. Yet, Streptomyces uses the hyphae to transport nutrients and chemicals and to communicate.

But when nutrients are missing, the branches grow out of the soil and into the air. Here, they form spores and produce geosmin and antibiotics. This geosmin attracts insects that distribute the spores in the environment.

Plus, by producing antibiotics, Streptomyces tries to kill those microbes that want to eat the spores.

The superhero of multicellularity: Magnetotactic multicellular prokaryotes

Ever since I heard about these bacteria, they became my favourites. And not only because these multicellular bacteria cannot even survive as single cells.

All cells within the magnetic berry are connected to a common core. On the outside of the berry, bacteria have flagella.

And because many of these bacteria assemble together and each one has several flagella, the whole berry is basically covered in bacterial flagella. When all of these flagella start rotating together, the whole berry becomes incredibly fast.

The second feature is, that these magnetotactic bacteria sense the Earth’s magnetic field lines thanks to their magnetosomes. Hence, this magnetotactic superorganism is even more sensitive to the Earth’s magnetic field, which gives it probably even more superpowers.

Lastly, the multicellular magnetotactic bacteria respond to blue light and swim away from it. This is a completely new bacterial ability and researchers are still not sure why these bacteria do that.

Unfortunately, we do not know much about these fascinating organisms, because they are incredibly difficult to grow in the lab. Until now, researchers could only image these bacteria from environmental samples as they still do not know what these bacteria need to survive in the lab.

Multicellular bacteria – an advanced lifestyle

As we have seen in this article, bacteria can grow either as single cells or as multicellular organisms.

By teaming up with their sibling cells, multicellular bacteria gain new superpowers, they can spread out and protect their weakest team members.

From an evolutionary point of view, forming multicellular organisms was a super important step. Only thanks to this, highly-developed animals with all their different cells and organs could develop.

The post Together we are strong – bacteria form multicellular organisms appeared first on Bacterialworld.
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 ?

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

Especially for the killing process, bacteria have a full arsenal of killer weapons at their disposal.

They can start a chemical war, burn their foes, roll over them or punch holes into them with a bow and arrow.

But each of these decisions comes with a price; they cost energy and resources.

Especially activating and shooting killer bows and arrows is incredibly costly for a bacterium.

So, before bacteria decide to kill, they need to take their whole environment into account.

Here, we will look at when bacteria activate and engage their nanoweapon, the type 6 secretion system.

A bacterial weapon to kill when needed

Bacteria have this incredibly efficient killer T6SS weapon that looks like a crossbow with arrows. They shoot these arrows together with toxins into their foes to kill them and get rid of them.

However, you can probably imagine that bacteria can’t just fire these arrows randomly all the time. Producing the machine as well as the arrows costs a lot of energy. Hence, bacteria need to make sure they only produce and fire this weapon when it is required. Or that they gain something out the kill – like when they protect their hosts from intruders. So, they need to decide well.

Two recent studies (here and here) looked at four different bacterial species from the Vibrio genus. They focused on these bacteria because they all have very similar bacterial nanoweapons but seem to use them differently.

Also, some bacteria from the Vibrio genus can cause diseases in us or marine animals. Hence, research focuses on these bacteria to better understand them.

Two proteins control the killer weapon

Generally, bacteria from the Vibrio genus use two proteins to control when to produce their T6SS weapons. We will call these two controllers protein X and protein Y.

Interestingly, in these species, protein Y also controls the motility of the bacterial cell. So, this protein regulates how active the bacterial rotor, the flagellum, is. If it’s rotating very fast, the bacterium can swim forward. If the rotor is quiet, the bacterium stands still.

On the other hand, protein X controls an activity called competence. Bacterial competence means that the bacterium produces a special machine on the cell surface. This machine picks up free DNA from the environment. Once a bacterium takes up external DNA, it can stitch the new DNA into its own DNA. Now, this bacterium has new “powers” depending on what the new DNA is for.

These two studies looked at the links between the two controller proteins and the killing machine. And what they found, helps us better understand the bacterial lifestyle and decision-making.

Bacteria decide to kill and steal DNA

One main focus of research is on the bacterium Vibrio cholerae. This pathogen lives on seafood and can cause extremely dangerous diarrhoea in us. This is why it is important for researchers to better understand how this bacterium lives and survives in water and in the environment.

In Vibrio cholerae, both proteins X and Y control the T6SS weapon. As soon as Vibrio cholerae killed a neighbouring bacterium, protein X activates the competence machine. Now, the bacterium can take up the DNA of the dead bacterium and integrate it into its own.

With this behaviour, Vibrio cholerae not only kills competitors but also evolves. After getting rid of a foe, it gets new DNA and thus new superpowers for challenging conditions.

However, sometimes Vibrio cholerae realises it does not have a chance against its competitor. In this case, protein Y activates motility and the bacterium can swim away and escape the predator.

Bacteria decide: should I kill or should I go?

Then, both studies looked at whether the control of the T6SS weapon works similarly in other Vibrio species. They looked at these bacterial species:

• Vibrio parahaemolyticus, which causes diarrhoea and lives in seafood
• Vibrio fischeri, a squid symbiont
• Vibrio alginolyticus, another seafood-poisoning cause

All of these bacteria live in marine environments and can live in fish or seafood. Since they all cause some form of diarrhoea, researchers try to understand these bacteria better to inhibit the diarrhoea-causing mechanisms.

Both Vibrio parahaemolyticus and Vibrio alginolyticus have two T6SS weapons while Vibrio fischeri only has one. Interestingly, they are all active at different temperatures, so bacteria already control their killing activity depending on how warm or cold it is.

Also, proteins X and Y control each T6SS weapon completely differently in each bacterium. There is no pattern. None.

So, why would very similar proteins have completely different impacts on the T6SS weapons in different bacteria?

And does this mean bacteria decide differently about whether to kill or not?

There is currently no clear answer to this. So, my guess would be that it depends on the killing power of the T6SS weapon. Some T6SS weapons can kill other bacteria. Then it makes sense to activate the competence machinery at the same time. Like this, the attacker bacterium can also take up the dead bacterium’s DNA. 

However, other T6SS weapons are supposed to kill higher species, like fungi or amoeba. But a bacterium could not use the DNA of such a species. In this situation, the competence machinery is not needed. Rather, motility would be more appropriate to escape this dangerous situation.

It remains mysterious around this T6SS killer machine and how bacteria decide to kill. Or not.

The post Should I kill or should I go? Bacteria making decisions 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

And sometimes, they use a chemical to kill other bacteria. This chemical is the so-called bacteriocin – a molecule produced by bacteria that is toxic against other bacteria.

But interestingly, these bacteriocin chemicals are not only to kill. They also help bacteria communicate and let them know about external attacks.

This mechanism might even give bacteria some kind of conscience. They work together to understand that they are under attack and then they decide to launch a massive counterattack.

This strategy to produce the bacteriocin is a bit complex, so we will explain it in more detail here.

Bacteria produce bacteriocin – another mechanism of bacterial warfare

Researchers knew for a while that some bacteria produce a group of molecules that they called bacteriocins. These bacteriocins are toxic proteins. And they mean to kill bacteria from the same family as the producing bacterium.

But when a bacterium produces such a bacteriocin, it also risks killing itself with it. This is why this bacterium also needs to produce an immunity protein. This immunity keeps the bacteriocin inactive so that the producing bacterium is safe from its toxicity. 

Additionally, bacteria produce a lysis protein. This lysis protein dissolves the membrane of the producing bacterium. So, once the bacterium produced a lot of the bacteriocin, the bacterium dies and releases the molecules into the surrounding. Here, the bacteriocin comes into contact with other bacteria to kill them.

How to investigate that bacteria produce bacteriocin

So, when one bacterium decides to commit suicide, it actually means killing those surrounding bacteria. What an altruistic strategy.

But, obviously, bacteria need to regulate the production of these three proteins very tightly. Otherwise, they might risk killing themselves or their sibling for nothing.

This is why researchers are investigating how bacteria regulate this process. And they found, that bacteria even use this strategy to talk to each other to send alarm signals.

For this, researchers looked at two bacterial family members that produce two different kinds of bacteriocins. And they put these two bacteria right next to each other and let them grow. After a while, both bacteria have doubled so many times that researchers could see these bacterial colonies with the eye.

In the picture below, you can see these colonies as two big black spots. However, here neither bacterium actually produces the bacteriocin.

Bacteria attack

In the next experiment, the bacteria in the right spot produce their bacteriocin. So, they are ready to kill.

The bacteria in the left spot do not produce a bacteriocin but instead, they have a so-called reporter. This reporter gets activated when the bacterium WANTS to produce a bacteriocin. And when the reporter is active, the bacterium turns green.

Now, bacteria in the right produce a bacteriocin to kill the bacteria in the left spot. And this works as you can see that the left spot is a bit smaller than the right spot.

Plus, the left spot now turns green. This green region is right next to the killing zone. Thus, it seems as if the remaining bacteria here are getting angry and turning into green little Hulks. This means they would like to produce bacteriocin to counterattack the bacteria in the right spot.

Bacteria fight back

Next, researchers wanted to know what happened if bacteria could actually fight back. So, they gave bacteria in the left spot also the ability to produce their bacteriocin. Now, bacteria in both spots could produce bacteriocin to fight.

And that is exactly what they do.

You can now see the killing zone in both spots. This means that bacteria in both spots are dying. 

Also, almost the whole left spot turned green. Previously, only a small zone close to the killing zone was green. Instead, now all bacteria in the left spot are ready to counterattack the bacteria in the right spot. 

Bacteria get angry and produce bacteriocin

From these results, researchers think that bacteria have some kind of competition-sensing mode. As soon as bacteria realise that there is danger, they talk to each other. Now, they can assemble and fight off the attacker as a team.

Basically, someone angers you, so you get angry. Now, you call up your friends to come together and put an end to it.

Are bacteria social because they produce bacteriocin?

In this study, researchers showed that bacteria have some kind of social behaviour. The idea is that when bacteria are under attack and start dying, they tell their siblings about it. Now, the others can prepare themselves to fight off the attacker.

This behaviour is pretty altruistic and incredibly smart of bacteria. Even though a bacterium is dying, it wants its sibling – and thus its species – to survive.

What do you think? Do you think is altruistic behaviour is worth to safe the rest of the family? Let me know your thoughts in the comments below!

The post Bacteria talk about bacteriocin so that they assemble and battle as a team appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

How does this bacterium make sure it won’t be disturbed in its new quiet environment? Easy – it builds a house to protect itself and its siblings.

But a bacterial house is a special one – we call it a bacterial biofilm. And bacteria form a biofilm when they want to protect themselves from their surrounding, form communities and grow and reproduce.

Let’s read on to find out what these bacterial houses are and how they build them.

Why do bacteria form a biofilm?

Just like you need a roof over your head to protect yourself from the outside weather, bacteria form a biofilm that works like a house. And they build these houses from scratch.

A bacterial biofilm has protecting walls and a roof around it. These barriers defend them from all sorts of stresses of chemical or mechanical nature.

And there are so many advantages for bacteria to live in such a house:

• Most antibiotics cannot penetrate biofilm so that bacteria are safe inside.
• Bacteria keep their own nutrients and water and oxygen within the biofilm.
• In the case of desiccation or starvation, they can survive inside.
• Immune cells cannot break through a biofilm, hence bacteria inside are protected from the host immune system. 

So, basically, a biofilm is the master accommodation for bacteria. 

Where do bacteria form a biofilm?

Biofilm is the stuff that you can feel on your teeth in the morning after you woke up. But don’t worry, you easily brush it off your teeth. 

Biofilm is the gloomy stuff that grows on your kitchen sponge and it is the crust in your kitchen sink if you haven’t cleaned it for a while.

Some bacteria can form a biofilm on contact lenses, which can lead to eye infections.

Unfortunately, bacterial biofilms are also one of the major burdens in hospital settings. Here, bacteria form biofilms on medical devices like catheters, joint replacements, implants or pacemakers.

Researchers even found microbial biofilms in 3.2 million-year-old fossils from volcanoes.  

So, generally, bacteria can form a biofilm on any surface.

What does a microbial biofilm consist of?

Many microbes and especially bacteria can form a biofilm. And dependent on the microbial and bacterial species, the biofilm can have a different colour, thickness and texture. 

Generally, biofilms consist of bacterial cells (either only one species or many different ones), as well as other microbes as for example viruses or phages. All these microbes inside the biofilm talk to each other and communicate.

Inside the biofilm, bacteria glue themselves together with so-called extra-polymeric substances. These are big molecules that bacteria produce and excrete.

These extra-polymeric substances are proteins, lipids, sugar molecules or polysaccharides and DNA. And these substances give the biofilm its gloomy or slimy texture.

Interestingly, each microbe and bacterium produces a slightly different kind of polysaccharide. And each of these polysaccharides has slightly different chemical properties. This makes the texture of biofilms from different bacteria also slightly different.

Within the biofilm, bacteria can store everything, for example, metal ions bound to DNA, nutrients like sugar, bacteriophages, oxygen… And bacteriophages even protect the bacteria inside the biofilm.

How do bacteria decide to form a biofilm?

This is an important question scientists are currently trying to understand. As soon as we understand how bacteria regulate biofilm formation, we might be able to develop drugs that prevent bacteria from biofilm formation. 

There is a general model of how bacteria form biofilm.

The general idea is that a few bacteria attach to a surface. For this, they use special adhesion proteins that help stick to the surface.

Now, bacteria want to settle down so that they do not need to move anymore. This is why they stop all movement mechanisms like swimming.

As mentioned already, inside the biofilm, bacteria talk to each other. Like this, they know when they are many together and they can start producing these extra-polymeric substances. By excreting them, bacteria get glued to each other. This helps them completely encapsulate themselves with this hydrogel. 

Interestingly, once in a while, a bacterium spontaneously explodes. Then, the other bacteria use the cellular content (so all the DNA and proteins and lipids) of the dead bacterium to form more biofilm.

Inside such a so-called mature biofilm, bacteria happily grow and divide inside.

However, as soon as nutrients become scarce inside the biofilm, the bacteria need to find a new place to live. Then they will start producing scissors to break the biofilm. And when they activate their swimming and motility motors they can detach from the biofilm towards a new place where they start all over again.

How do we research bacterial biofilms?

This is actually pretty easy, as there are many different stains that specifically bind to bacterial biofilm and make them visible. In the picture below you can see two examples.

These are two different stains that visualise bacterial biofilms. With the stain crystal violet, we can see a purple ring of biofilm on plastic and with congo red, we can visualise the structure of a biofilm.

In the above picture, in the left column (PAK) is a biofilm of the bacterium Pseudomonas aeruginosa. This one does not make much biofilm because you can barely see any violet or red stain. The other two columns are different mutants that produce more biofilm. These biofilms you can recognise by the strong violet or red colours.

With these experiments, researchers can understand under which conditions bacteria form more or less biofilm or whether their texture changes. This will eventually help us get a clearer picture of the fascinating life of bacteria and how to counteract them.

We still don’t understand biofilms very well. And so far we know that some enzymes exist that break a biofilm apart. However, the big goal would be to prevent bacteria from forming biofilms in the first place.

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

And just like in your life, these interactions can be good or bad for both parties. Also, bacteria can either help or fight each other.

Interestingly, bacteria developed very efficient killer weapons to go to war with other microbes.

Here, we will talk about one of these weapons – the so-called contact-dependent growth inhibition system. Or as researchers also call it:

Death on a stick

What is contact-dependent growth inhibition?

The name of this weapon is more of a concept than a physical machine. So, let’s start by breaking this phrase apart.

Contact-dependent growth inhibition: “contact-dependent” means that a bacterium needs to be close to and in physical contact with the other bacterium for this system to work. “Growth inhibition” means that the bacterium with this system restricts the growth and reproduction of other bacteria. In other words, it kills these bacteria.

So contact-dependent growth inhibition is basically a weapon to kill other bacteria. And interestingly, researchers managed to take a snapshot of this weapon. It indeed looks like a stick on the outside of the bacterial membrane.

Imagine, how tiny a bacterium is. And on the outside of this tiny bacterium sits an even tinier killer weapon!

Okay, now that we understand what this contact-dependent growth inhibition system is, let’s look at how it actually works. How can a little stick be so dangerous to other bacteria?

How does the contact-dependent growth inhibition weapon work?

To answer these questions, we need to first understand what this stick weapon is built of.

In the picture below you have two bacteria and one stick weapon. The bacterium at the bottom is the attacker with the stick poking out of the membrane. The bacterium above is the prey that will get killed.

And in that picture, you can see that the stick weapon consists of three parts: the proteins A and B and an immunity protein.

Protein B (brown) can make holes in membranes.

Protein A is huge and has many different parts with different functions (hence the different colours in the figure). At the very end of protein A is a toxin (red) that can break the prey cell apart.

This is why the attacker bacterium needs to have an immunity protein (grey). This protein binds to the toxin and keeps it from breaking the attacker cell apart.

What are the different steps of killing?

So, our attacker lives in a nice environment minding its own business. And just in case, another bacterium becomes annoying, our attacker produces this stick and have it poking out of the cell. However, the main part of protein A sits and waits inside the attacker.

When another bacterium comes into contact with our attacker, the green part of protein A binds to this prey. This activates the stick and protein B helps protein A pass through the hole to the outside.

Now, the yellow part of protein A inserts itself into the membrane of the prey bacterium. This allows the last bit of A to travel through the prey’s membrane and cut itself loose from A.

Next, the orange bit of A binds to a specific transporter in the inner membrane of the prey so that it imports the toxic domain (red). It is unlikely that the prey bacterium has the matching immunity protein (grey) for this attacker’s toxin. Hence, the imported toxin domain can damage the bacterium and even kill it. 

Why did bacteria evolve these cool contact-dependent growth inhibition weapons?

As you can understand, the contact-dependent growth inhibition weapon is a very complex mechanism and not every step is completely understood yet. That’s why researchers keep investigating this system so that we might be able to use it to our own advantage.

One theory is, that bacteria use this system to distinguish between siblings and non-siblings. Only a sibling bacterium would have the right immunity for an attacker’s stick weapon and thus survive an attack.

Other bacteria with different toxins and immunities would be killed. These bacteria likely belong to a different family and should thus be excluded from the community. 

This would help bacteria connect only with family members and form exclusive networks for only like-minded (or -powered) bacteria. Even though these are only theories, it seems that also bacteria are very picky when it comes to choosing their friends and family. As we said in the beginning, social interactions can be helpful or harmful.

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

And this food exchange is what makes bacteria and their interactions so incredibly fascinating. Bacteria can fight each other to get rid of competitors or they are nice to each other and share food.

But how do bacteria feed each other? How do they know that they have a friend in need of food? And how do they actually exchange the food?

Read on to find out how.

How bacteria make stuff

First, we need to understand how bacteria actually produce stuff and what proteins are made of.

Bacteria and all living organisms use their DNA as a transcript. They read this transcript and produce long chains of amino acids from it. This chain is what we call a peptide. And this peptide eventually folds into a protein.

Most organisms use twenty amino acids to make their proteins. And since these amino acids can link together in any random distribution, proteins can look completely different. They have all sorts of different sizes, shapes, functions, binding sites, etc.

Now, these amino acids are like LEGO bricks that can be linked together in a million different ways and the outcome is always different (which is why proteins are so different). To produce all the necessary proteins, each amino acid needs to be present within a cell.

But not all organisms can produce all amino acids. For example, we need to make sure that we take up certain amino acids with our food since we cannot make them ourselves. Similarly, some bacteria need to find certain amino acids in their environments to make all proteins so that they can function properly.

How bacteria feed each other

A new study found that some bacteria can actually help each other when one of them is in need of a specific amino acid. In this case, the bacteria form tubes between them to exchange cellular content. These tubes are called nanotubes and bacteria use them to exchange nutrients to ensure the receiving cell survives.

To better understand this sort of food exchange, the researchers used the idea that bacteria need all of the amino acids to survive. So, they wanted to show that two different bacteria can help each other out with certain amino acids. For this, they created two bacteria with different abilities – so-called strains:

• one strain produced a lot of amino acid W and no amino acid H

• the other produced a lot of amino acid H and no amino acid W

W and H are the codes for the two amino acids Tryptophane (W) and Histidine (H).

In the experiments, the researchers then grew the bacteria in a medium that did not contain the amino acids W and H, but all the other ones. They grew the bacteria:

• together so that they would be in close contact
• together but with a separating “wall” 
• on their own

Neither of the bacterial strains could survive on their own as each was missing one amino acid. Also, when the two bacterial strains grew in the presence of a wall, neither of them survived.

Interestingly, only when they grew closely together, did both bacteria survive. This meant that the two bacteria needed to have direct contact with each other to survive. Also, the survival of both bacterial strains completely depended on each other.

Bacteria form nanotubes to feed each other

When the scientists then took a closer look at the bacteria, they saw that the bacteria formed some kind of nanotube between the cells. And they are convinced that the bacteria use these nanotubes to exchange nutrients and feed each other with essential food.

It is as if you and your neighbour both want to make a cake but they miss the eggs and bought too much flour while you forgot to buy flour and got too many eggs. Neither of you would be able to make the cake on your own. So you need to dig a tunnel between your flats to exchange eggs and flour and you can both bake your cakes.

However, now the interesting question one might ask is how do you know that your neighbour needs eggs and how do they know that you have enough to share? You cannot just start digging a tunnel hoping that your neighbour has the things you need.

So how does one bacterium know that the other one is in need of a certain amino acid? We know that bacteria do talk to each other, but they certainly will not call or send the other guy a message on WhatsApp… 

And also, what is it that the bacteria actually exchange? Do they send the amino acid itself (hence the eggs) or do they send the DNA so that the other cell can learn how to make the amino acid? This would mean you send your neighbour a chicken so they can produce their own eggs…

We now better understand how bacteria can feed each other and make sure their friends survive. Yet, there are still many unanswered questions about this interaction. Hopefully, we will have some answers to them soon.

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