Biofilms Protect Bacterial Communities

green and blue bacteria colonies and molds in a petri dish

Biological Strategy

Salmonella

Natalie Chen

Image: Jeroen Fortgens / Shutterstock / Public Domain - No restrictions

Cooperate Within the Same Species

A species is a group of organisms capable of breeding to produce fertile offspring. When individuals within a species undertake activities that benefit one another, that cooperation benefits not just the individuals, but also local and wider populations of that species. Collaborating in activities such as finding food, controlling parasites, and protecting from predators enhances overall survival. To cooperate, there must be enough benefit to an individual, and especially to a population, to justify any risk taken by individuals. Through cooperation, risk is distributed among individuals and the benefits to the community are greater than the sum of the benefits to individuals. An example is birds that gather in flocks, a cooperative activity more beneficial than acting alone. While some birds forage, others watch for predators. When one finds food, others also feed on it. Despite potential short-term competition for an individual that finds food, over the long-term, that same individual benefits when others find different food sources.

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Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

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Protect From Chemicals

Chemicals are everywhere in the bodies of living organisms and their external environments. While most chemicals are valuable or benign, some are toxic, including those used for defense (such as the mucus that protects clownfish from an anemone’s stinging tentacles). Even naturally-occurring chemicals, such as arsenic, must be managed to reduce their impact. Some living systems have strategies to break down harmful chemicals, alter them into less toxic forms, physically prevent chemicals from harming sensitive tissues, and more. For example, some herbivorous mammals can digest toxic compounds in plants because they have a particular enzyme that helps them process poisonous plant compounds.

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Bacteria

Domain Bacteria (“small staff”): L. acidophilus, Staphylococcus

From inside of our own bodies to the deepest parts of the ocean, bacteria have adapted to almost every possible environment. All bacteria are unicellular, microscopic, and lack a membrane-bound nucleus and organelles, and come in three basic shapes: spherical (cocci), rod (bacilli), and spiral (spirilla). Some strains can be deadly, like Staphylococcus aureus (MRSA) while others, like Lactobacillus acidophilus, found in our intestinal microbiome, keep us healthy. Cyanobacteria, also known as blue green algae, caused the Great Oxidation Event 2.4 billion years ago, producing Earth’s first oxygenated atmosphere.

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Bacteria rely on social cooperation to produce a biofilm that protects the community

Bacteria are tiny cells that can enter the human body and cause infections that make humans sick. In order to get better, the body needs to kill or stop the growth of these bacteria. Doctors give medicines called antibiotics to help the body get rid of an infection. Penicillin is a common antibiotic often used to stop bacteria from growing. It does this by preventing the bacteria from building a cell wall, which makes it difficult for it to grow and reproduce. However, bacteria can build resistance, or develop a defense against antibiotics. Random changes can happen to the bacteria’s genetic material, or DNA. DNA provides instructions that tells the cell how to operate. Certain changes in DNA can result in changes to a bacteria that make it resistant to an antibiotic, and this makes the antibiotic less effective at killing the bacteria.

Another way bacteria can protect themselves from antibiotics is to form a ‘biofilm’. A biofilm is a substance produced by bacteria that covers them and protects them from harm. Biofilms are the source of more than 60% of bacteria-causing diseases. For example, slimy films in swamps are biofilms. Forming biofilms is a social strategy that helps to protect bacteria. It can physically prevent antibiotics and disinfectants from coming close to the cell. It also protects the cell from removal by physical means, such as wiping or washing away on surfaces.

Although biofilms are very useful, bacteria need to use energy and resources to grow them. Bacteria expel different substances to build and maintain the biofilm. A group of bacteria working together is called a colony. The colony needs all the cells to work together to grow and maintain the biofilm. Creating biofilms can benefit any cell underneath the film, even if some bacteria don’t produce the necessary substances. To visualize this, imagine a community of 50 people holding up a blanket to protect themselves. The blanket needs to be held up to be useful. Of the 50, 10 people may not be holding up the blanket but they will still be protected. However, if only 1 person is holding up the blanket then it will fail to protect everyone.

This strategy helps to strengthen the bacterial community as a whole. For it to work, a majority of the colony is expected to take part. Because there is a cost in energy and resources to produce the biofilm, if certain bacteria are not making the substances they can grow faster than those that are. Eventually, these bacteria will outnumber those putting energy into making the biofilm. Over time, there will be less bacteria contributing to making the biofilm and it won’t be as good at protecting all the bacteria. This makes them more vulnerable to antibiotics or being removed from surfaces.

Scientists are studying how bacteria make biofilms to help develop more effective antibiotics. They have developed a chemical (5-aryl-2-aminoimidazole-based inhibitor) that can stop bacteria from making biofilms. This makes it easier to kill the bacteria with antibiotics and makes it easier to remove them from surfaces.

To learn more about this biofilm inhibition strategy, watch this video from KU Leuven.

Image: CDC/ Rodney M. Donlan, Ph.D.; Janice Carr (PHIL #7488), 2005. / Public Domain - No restrictions

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References

“Biofilms are a major form of microbial life in which bacteria form dense surface-associated communities, typically enclosed in a matrix of self-produced exopolymeric substances (EPS). Bacteria within biofilms are up to 1,000 times more tolerant to antibiotics, disinfectants, mechanical removal, and other stresses, and this tolerance heavily impedes antimicrobial treatment. Hence, persistent biofilm infections and contaminations widely occur and cause a tremendous amount of problems in various sectors, including medicine, food industry and agriculture. This urges the need for strategies that inhibit biofilm formation and render microbes susceptible to treatment.” (Dieltjens et al. 2020: 2)

“Social evolution theory predicts that inhibiting public goods inhibits bacterial growth and survival, and that, critically, strains resistant to the public good inhibitor will be counter selected. The reason is that a resistant strain will produce the public good and pay a cost to do so, while susceptible strains will be able to use the public good without paying the cost.” (Dieltjens et al. 2020: 2)

Journal article

Inhibiting bacterial cooperation is an evolutionarily robust anti-biofilm strategy

Nature Communications | 09/01/2020 | Lise Dieltjens, Kenny Appermans, Maries Lissens, Bram Lories, Wook Kim, Erik V. Van der Eycken, Kevin R. Foster & Hans P. Steenackers

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Reference

“Much of the social activity of P. aeruginosa involves cooperation through the secretion of public goods. ‘Public good’ is an umbrella term used in the microbial social evolution literature to refer to a resource, such as a secondary metabolite, that is secreted by bacteria and becomes publically available to other cells within a population. Many public goods are costly to produce, making them susceptible to exploitation by cheater strains that benefit from the public good without producing it themselves.” (Boyle et al. 2013: 207).

“Biofilms, in particular, may be the norm rather than the exception: an often cited number is that 60% of all human bacterial infections involve biofilms.” Boyle et al. 2013: 207)

Journal article

Exploiting social evolution in biofilms

Current Opinion Microbiology | 01/04/2014 | Kerry E. Boyle, Silja Heilmann, Dave van Ditmarsch, and Joao B. Xavier

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