Bacteria building houses

Bacteria can be major problems for human health. One of the reasons for that is because they have the ability to form biofilms. 

What is a biofilm you ask?

I am glad you’re here.

Bacterial biofilms are defined as a structured consortium of microbial cells surrounded by a self-produced matrix. 

This means a bacterial biofilm can be understood as a self-built house. It is like bacteria have protecting walls and a roof around them. Such biofilm protects them from all sorts of stresses either of chemical or mechanical nature.

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

So, basically, a bacterial biofilm is like a master accommodation for bacteria. 

But where do we find biofilms?

Components of a mixed biofilm from a sulfure spring.
(a) Light microscopy of biofilms with Archaea arranged like a chain of pearls
(b) Electron microscopy of biofilm showing dense bed of Archaea
(c) Electron microscopy of biofilm showing Archaea,Bacteria, EPS structures, and the fungus Mucor hiemalis
Picture was adapted from Hoque and Fritscher, 2017.

Biofilm is the stuff that you can feel on your teeth in the morning after you woke up and that you then brush off your teeth. 

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

Some bacteria can form biofilms on contact lenses, which can then lead to eye infections.

One of the major burdens in hospital settings is bacterial biofilm that is formed on medical devices like catheters, joint replacements, implants or pacemakers.

Biofilm was even discovered in 3.2 million year old fossils from volcanoes.  

Taken together, bacteria can form biofilms on almost any surface like contact lenses, skin, host cells, plastic, plants and so on…

What does a biofilm consist of?

Not all bacteria are able to form a biofilm and dependent on the bacterial species, the biofilm can have a different colour and thickness and texture. 

Biofilms consist of bacterial cells (either only one species or many different ones), that are glued together by so-called extra-polymeric substances. These substances are found extra-cellular and are of polymeric structure, which means they are big molecules that are produced and excreted by bacteria.

These extra-polymeric substances are proteins, lipids, sugar molecules or polysaccharides and DNA, which give them their gloomy texture. Each bacterium produces a different kind of polysaccharide that makes up the biofilm, which is why the texture of biofilms can be different.

Inside the biofilm, basically everything can be stored for example metal ions that are bound to DNA, nutrients like sugar, oxygen…

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 inhibit biofilm formation. 

There is a general model of how bacteria form biofilm which I tried to sketch in the picture below. 

It is generally understood, that a couple of bacteria attach to a surface. To do this, they use adhesion proteins, the same ones that were discussed in the article “how bacteria get too attached“.

Then bacteria stop expressing proteins that they would usually use for movement like swimming. They want to settle down now and become lazy, so no moving required anymore. 

Now, they start producing these extra-polymeric substances. By excreting them, bacteria get glued to each other until they are completely encapsulated by some kind of hydrogel. 

Interestingly, once in a while, one bacterium spontaneously explodes and its cellular content (so all the DNA and proteins and lipids) is being used as a foundation for biofilm. Researchers could actually visualise this recently and a video showing exploding bacteria is below.

After they have established a so-called mature biofilm, bacteria happily grow and divide inside and also communicate with each other.

As soon as nutrients become scarce inside the biofilm, they need to find a new place to live. Then they will start producing their swimming and motility motors and detach from the biofilm towards a new place where they start all over again.

How do we research biofilm?

This is actually pretty easy, as there are many different stains that specifically bind to bacterial biofilm and make them visible. Two examples are shown in the picture below.

These are two different assays that visualise biofilm formation of our lab bacterium which is Pseudomonas aeruginosa.
With a biofilm assay we can see a purple ring of biofilm on plastic and with a congo red assay we can visualise the structure of a biofilm.
In the left column (PAK) is a biofilm of the wildtype bacterium. The other two columns are different mutants from the same bacterium that produce more biofilm that is also structurally different. Hence the darker purple and red colour.
Picture was adapted from Bordi et. al.

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

2 thoughts on “Bacteria building houses

  1. Are biofilms the reason why disinfectants kill only 99% of bacteria or because of other resistances, or both? Or are disinfectants actually an effective way of penetrating the biofilm and killing the bacteria inside?

    Liked by 1 person

    1. That is a great question and I was just skimming through the current literature. It seems that bacteria grown in a biofilm are generally a lot more resistant to disinfectants than planktonic (swimming) bacteria. This is a major problem in hospital environments as it is super difficult to completely get rid of a bacteria once they have established a biofilm.

      Liked by 1 person

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