But what do bacteria and fungi use antibiotics for? Why do they produce them? And what are the advantages of microbes having antibiotics as molecular weapons?

What are antibiotics?

The father of antibiotics, Selman Waksman, first used the word antibiotics for any small molecule made by a microbe that can inhibit the growth of other microbes.

So, microbes – especially bacteria and fungi – use antibiotics to kill other microbes. These other microbes can be bacteria, fungi or bigger organisms. Not viruses though!!!

Why not viruses?

Because antibiotics bind and inhibit cellular machines in living organisms. These molecules often bind to so-called targets. Antibiotic targets can be proteins or enzymes that make for example the cell wall, other proteins or components of the respiration complex.

These proteins are generally essential. So, when antibiotics inhibit the proteins, the cells are missing these essential functions. And without them, they cannot survive and die.

Hence, like other bacterial toxins, antibiotics are lethal.

Interestingly though, bacteria and fungi make antibiotics from simple building blocks. These are present in every cell and can be amino acids, lipids or even sugars.

But instead of using these building blocks for their normal functions, microbes link them together in different ways. With this, they create new – and fancier – molecules that barely resemble the original blocks.

Then, they transport these antibiotics to the outside or send them off in outer membrane vesicles. When the antibiotic hits another microbe, there are two possibilities: either the microbe is resistant to the activity of the antibiotic or it dies from it.

But what about the microbe that produces the antibiotic? Is it resistant to the antibiotic itself?

Why are microbes that produce antibiotics not get killed?

Since antibiotics are meant to KILL other microbes, then why do producing microbes not get killed by their own antibiotics? The answer is self-protection!

Whenever bacteria or fungi produce antibiotics, they always also produce some sort of self-protective means. Just as when bacteria produce other toxins, they always need to make sure they are not killed by their own weapons.

These self-protectors usually keep the antibiotic in an inactive state. For example, they completely surround the antibiotic molecule so that it cannot bind to its usual target within the cell. Another strategy is to add a small molecule to the antibiotic – again to keep it from binding to its target.

Then, when the microbe is ready to transport the antibiotic outside of the cell, it takes the self-protection off the antibiotic. This releases only the toxic part – the antibiotic itself – into the surrounding.

Note, however, that these self-protection mechanisms are not antibiotic resistance mechanisms. Self-protection mechanisms are meant to inactive antibiotics only temporarily. Hence, these mechanisms are reversible. The antibiotic can still become active and thus toxic.

Resistance mechanisms, on the other hand, are meant to inactive antibiotics permanently. Hence, these mechanisms are irreversible. Since this usually completely destroys the antibiotic, it cannot become active anymore.

But what triggers microbes and especially bacteria to produce antibiotics? How do antibiotics help the producing cell in their daily circumstances?

Why do bacteria produce antibiotics?

To answer this question, we need to look at where the bacteria live that make antibiotics. And two-thirds of the known antibiotics are made by bacteria from the Actinobacteria family. Within this family, Streptomyces is the best-known member that produces half of all known antibiotics.

Another example is bacteria from the Myxococcus family. So, where do Streptomyces and Myxococcus bacteria live? Interestingly, these bacteria call the soil their home.

And in the soil, they often confront lots of friends and foes. And they need to constantly fight for their own survival.

Myxococcus is known as a wolf-pack predator because it kills its prey in massive attacks. Colonies of Myxococcous roll over their prey, secrete antibiotics and thus kill them and feed on them.

Streptomyces, on the other hand, uses its antibiotics a bit more civil.

To move in the environment, Streptomyces bacteria grow as long filaments throughout the soil. They build long chains and branch out into the soil as multicellular organisms. These branches are filled with Streptomyces cells but also spores so that the bacteria can extend to new places.

When the bacteria hit a period of bad weather or don’t find much food, they release their spores as a survival strategy. Plus, they start releasing nutrients for the spores. But these nutrients also attract other organisms like bacteria.

Hence, at the same time, Streptomyces produces a huge amount of antibiotics to fend off these putative food-stealers. Like this, Streptomyces makes sure their spores are safe and can survive in their new homes for a while.

How do antibiotics produced by bacteria help others?

Like Streptomyces, lots of bacteria use antibiotics to fight off predators. This assures their own survival and that of their species.

Yet, more and more research finds that bacteria not only kill other species with antibiotics so they can survive. The killing also benefits their hosts.

For example, the bacterium Janthinobacterium lividum lives on frogs where it produces the antibiotic violacein. This antibiotic kills fungi so that the bacterium protects the frog from deadly fungal infections.

Also, a bacterium that lives in our noses is the harmless Staphylococcus lugdunensis. This bacterium produces the antibiotic lugdunin. That inhibits the harmful Staphylococcus aureus from settling down in our noses. Now, scientists look into how we could use the harmless Staphylococcus lugdunensis to protect us from infections.

Another example of microbes that produce antibiotics to help others is the three-member association of ants, Streptomyces and a fungus. Several species of ants grow fungi for food. They feed their fungi with fresh plants and let them grow in special underground gardens.

To not contaminate these fungal gardens, ants carry symbiotic Streptomyces that produce antibiotics. Like this, the antibiotics kill other microbes and keep the fungal gardens free of harmful intruders. As a thank you, the ants feed the Streptomyces and give them a place to live.

About antibiotic-producing microbes

So, just as we use antibiotics to kill harmful bacteria and fungi, antibiotic-producing microbes do the same. They want to fight off predators and assure their own survival.

When you think about it: we use their own killer weapons against them. Poor microbes!

The post Bacteria use antibiotics to kill their foes and protect others appeared first on Bacterialworld.
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

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.

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