The Universe of the Intelligent Microbe--The Biofilm

Revelation at Snowpatch Spire

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This picture of Snowpatch Spire is credited to BeiJiaLi and is used under a Creative Commons Attribution-Share Alike 3.0 Unported license.

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It was while preparing to climb Snowpatch Spire, in British Columbia, that J. W. Costerton observed the abundance of biofilm under the surface of Bugaboo Creek. From Costerton's observation grew insight into the role of biofilm in nature, and in human disease. This is an insight he described in his landmark research paper, How Bacteria Stick. The experiments and discoveries that followed from Costerton's observations are briefly discussed in the third paragraph of this blog.

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Biofilm: Antagonist and Ally

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Imagine a colony of microscopic life in which all parts are connected by a gelatinous, impenetrable mass. Imagine that these tiny bits of life do not operate independently, but send messages back and forth to each other so they can provide for the common defense, acquire food, propagate--and invade. This gelatinous mass spreads across the earth, so that it becomes the most abundant form of life on the planet. Science fiction? No. It's all true. This gooey, invasive mass is called a biofilm and it is formed by microorganisms. It may be both helpful and threatening to human existence. It is the oldest form of life on earth. It populates oceans, lands--and, sometimes, very aggressively, human beings.

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Usually, when we think of bacterial infections, we imagine armies of microorganisms, swarming as they invade. In technical language, what we are imaging are bacteria in their planktonic form. In this form, they are free-floating, independently-acting microorganisms.

This is how most scientists also envisioned invading bacteria before 1978. It was the year in which University of Calgary biologists, J. W. Costerton, published a paper that described the ubiquity and relative impermeability of biofilms.

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Diagram of Maturing Biofilm (Featured Bacteria: Pseudomonas aeruginosa)

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This illustration, by D. Monroe, shows the stages a microorganism goes through as it becomes part of a biofilm. The first picture shows the organism in its individual state, as it is forming attachment to other individual microorganisms. Gradually this mass becomes a mature biofilm, a unified mass. Once the biofilm reaches maturity, it goes into the final stage, in which it disperses individual bacteria into the environment. These individuals will again begin the process of attachment and formation of a biofilm. The illustration was included in D. Monroe's research paper, "Looking for Chinks in the Armor of Bacterial Biofilm", published in PloSBiology. The image is used here under a Creative Commons Attribution-Share Alike 2.5 Generic license.

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Costerton's 1978 paper on biofilm was co-authored by G. G. Geesey, and K-J Cheng. Costerton's initial observation of biofilm came about by accident--literally. He fell into a creek. He noted that everything under the surface was covered by slime, and that the slime was filled with bacteria. Costerton recognized the ubiquity and significance of this slime--of biofilm. He described how biofilm not only proliferates in nature, but also in human beings, and in medical facilities. The bacteria that colonize within a biofilm demonstrate a kind of evolutionary intelligence, an obstinate will to survive.

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Bacterial Mats Near Grand Prismatic Spring in Yellowstone National Park

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The picture shows the formation of biofilms on the surface of a spring at Yellowstone National Park. The photo is credited to Daniel Mayer and is used under a Creative Commons Attribution-Share Alike 3.0 Unported license.

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Biofilms form through the cooperative action of bacteria. Bacteria in a free state (planktonic bacteria) adhere to one another and then become encased in a glycocalyx coating. This coating in many cases can be an insurmountable obstacle to the defensive action of the human immune system. Bacteria encased in biofilms are also resistant to most traditional antibiotics, and even to disinfectants. Persistent infections in people, and contamination of equipment, is often due to the presence of biofilms.

Though they can be dangerous in a medical context, biofilms are also essential to life on earth. A 2017 article in Applied Water Science describes how biofilm and aquatic plants exist in a mutually beneficial relationship. The plants provide the biofilm with carbon and oxygen. The biofilm offers the plant physical protection, (by creating a barrier film), and minerals. Together, according to this article, the plant/biofilm relationship also helps to reduce the effects of water pollution.

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Symbiotic relationships between biofilms and nature may also be found in aquatic animals. In the illustration below, the Hawaiian Bobtail squid demonstrates luminescence. This luminescence is part of the animal's survival camouflage and is created by a microbial biofilm, Vibrio fischeri, that colonizes the squid.

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This photo is credited to Chris Frazee and Margaret McFall-Ngai. It is used under a Creative Commons Attribution-Share Alike 4.0 International license.

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Other instances of beneficial biofilm relationships may be seen in terrestrial plants. A 2016 article, "Effect of biofilm forming plant growth promoting rhizobacteria on salinity tolerance in barley", in Annals of Agricultural Science, explains the application of biofilm/plant symbiosis in agriculture. In this case, biofilms are used to promote the growth of essential grains. The article describes how soil salinity affects the ability of barley to thrive, and how biofilms can make such soil more hospitable to plant cultivation, especially in the production of barley. Globally, barley is a very important food crop. Biofilms help in nutrient uptake, regulation of plant hormones, and enhancement of pathogen resistance. The authors of this article suggest that use of biofilm in highly saline soil may increase the amount of available arable land in the world by as much as 2%, annually.

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The Role of Biofilm in Disease

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Although biofilm may be essential in nature, it is a formidable opponent in medicine. The diagram of biofilm maturation shown earlier in this blog features Pseudomonas aeruginosa. While this colonizing bacterium is not usually a concern in a healthy population, in hospitals and among the vulnerable Pseudomonas wreaks havoc. It is a persistent and deadly foe. Once it invades the system of a compromised individual, it is extraordinarily difficult to eliminate. People who suffer from lung ailments are particularly susceptible because Pseudomonas thrives in mucus.

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In the pictures below, microscopic images of Pseudomonas are presented. The first shows individual Pseudomonas bacteria. The second shows bacteria that have formed a biofilm.

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In this picture(above), taken by Janice Haney Carr for the CDC with an electron microscope, individual Pseudomonas bacteria are shown. The image is in the public domain.

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In this picture (above), the blob on the right, which is larger and more reddish in tone, is a biofilm made up of Pseudomonas bacteria. The smaller blob is a biofilm made up of Staphylococcus aureus--Staph. Both types of biofilm are challenges in communal medical settings, such as hospitals and nursing homes. They are extremely resistant to antibiotics and disinfectants. The picture is credited to HansN and is used under a Creative Commons Attribution-Share Alike 3.0 Unported license.

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Pseudomonas and Staphylococcus are by no means the only bacteria that threaten health through biofilm formation. Biofilm formation plays a role in many diseases--some that may be commonly recognized are: Legionnaire's disease, plague and candida.

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All pictures in this blog may be found on Wikimedia Commons