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BIOFILMS

​In natural microbial habitats most of the resident bacteria, often in excess of 99.9 %, are attached to surfaces. Worldwide biofilm pervasive effects on human health, water quality, corrosion, and power generation cost billions of dollars annually. A biofilm is an assemblage of microbial cells that are irreversibly associated with a surface and enclosed in self produced extracellular material (EPS) primarily composed of polysaccharides, proteins, and nucleic acids. Any surface can serve as a starting ground for a biofilm development. Microbial biofilms may colonize industrial pipelines, kitchen sinks, nuclear power stations, air conditioning systems, water distribution systems, hospitals, plants, animals to name a few. Biofilm acts as a barrier and protects cells against immune system defense, reactive oxygen species, UV light, dehydration, metals, and antibiotics making it the most pervasive and enduring biological structure in nature.

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Biofilm formation

 

Necessary and sufficient conditions for biofilm formation require surface, microbial cells, and extracellular matrix. Biofilms may form on different surfaces and interfaces:

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  • solid-liquid

  • solid- air

  • liquid- air

  • liquid-liquid

 

Biofilm formation is determined by surface chemical composition, roughness, hydrophobicity, zeta potential and growth conditions.

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E. coli biofilms grown on glass surface in the rich medium supplemented with glucose (A), biofilms grown on PMMA surface in the rich medium supplemented with lactose (B) after 48 h of incubation. Zone I – arbitrarily designed high-density region where biofilm covered 90% or more of the available surface, Zone II – biofilm covered between 10 and 90% of the available surface, Zone III – biofilm surface coverage was less than 10%. Columns represent a low magnification DIC micrographs taken every 0.8 mm in the vertical direction from the water–air interphase (total depth 20 mm). Three representative higher magnification micrographs for different zones are shown on the right of the columns. Scale bar on micrographs represents 20 μm.

Biofilm cycle

 

Biofilm begins when free-floating microorganism attaches to the surface. Attachment is followed by a period of growth which results in microcolony formation. Further layers of microorganisms and EPS build upon the first layers that may mature in an elaborate and complex 3D structure. The amount of available nutrients can limit how much the biofilm can grow. Another environmental factor is shear stress. In high shear environment the biofilm is usually fairly thin. Finally, the cells within a biofilm can leave the fold and establish themselves on a new surface. Either a clump of cells breaks away, or individual cells burst out of the biofilm and seek out a new home.

credit to D. Rodriguez, B. Einarsson, and A. Carpio, Phys. Rev. E 86, 2012

Why forming a biofilm?

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  • more resilience to stress (i.e. lack of water, high or low pH, toxic substances such as antibiotics, antimicrobials or heavy metals)

  • the slimy EPS can act as a protective barrier, it can help prevent dehydration or act as a shield against ultraviolet (UV) light

  • division of labor, presence of different physiological groups (i.e. EPS producers, producers of surface active compounds, canibales, spore former)

  • cross-feeding (i.e. autotrophic and heterotrophic microorganisms that live together in biofilms).

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How Biofilms Affect Us?

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Given the vast range of environments in which we encounter biofilms, it is no surprise that they affect many aspects of human life. Below are a few examples.

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  • biofouling

  • biocorrosion

  • production of toxines (i.e. toxic agal blooms)

  • mobilization of toxic elements (i.e. mercury, arsenic and selenium)

  • production and consumption of green house gases

  • food spoilage and poisoning

  • public health: (i.e. otitis media, bacterial endocarditis, cystic fibrosis, Legionnaire's disease, cholera, inflamations)

  • failure of medial implants

 

The reason that biofilm formation is a great cause of concern is that, within a biofilm, bacteria are more resistant to antibiotics and other major disinfectants that you could use to control them. In fact, when compared to free-floating bacteria, those growing as a biofilm can be up to 1,500 times more resistant to antibiotics and other biological and chemical agents. Although our lates research cast some doubt on such figures.

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How we may benifit from biofilms?

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  •  Bioremediation (treating wastewater, heavy metal contaminants, explosives and radioactive substances. "Microbes can either degrade them, or change their mobility or their toxic state and therefore make them less harmful to the environment and to humans

  • biogas production (hydrogen or methane)

  • Microbial fuel cells (to convert organic waste into electricity. The microbes live on the surface of an electrode and transfer electrons onto it, ultimately creating a current).

 

 

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Our research on Biofilms

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  • We study the effect of surface on the initial attachment of bacteria (i.e. titanium alloys, glass and PMMA surfaces, mineral wool, tooth enamel)

  • We study the mechanics of biofilm pelicle formation.

  • We study the mechanical coupling between bacteria in dilute bacterial suspensions

  • We measure rheology of biofilms

  • We study biocide effect on biofilms

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