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Team:Glasgow/Biofilm
From 2011.igem.org
Biofilms
Bacteria are found in the environment in two forms: planktonic (single) cells and in diverse multi-species communities called biofilms. Although most lab strains of bacteria do not form biofilms in natural, industrial or medical environments this is the most common way that they are live. Biofilms form on surfaces, generally at an air-water interface, and have complex 3D structures that consist of microbes and a mixed of exo-polysaccharides and DNA excreted by some members of the biofilm.
Stages of Biofilm DevelopmentTo start the initial formation of a biofilm, founder microbes attach to a surface weakly through van der Waal forces and as long as they're not sweep away too quickly they attach irreversibly using fimbriae or pili that cover the outer surface of the cell. When they have attached they start to excrete a mixed of exo-polysaccharides and DNA called the extra-cellular matrix (ECM) which aids attachment to the surface and give protection from the surrounding environmental conditions. This “proto-biofilm” now grows in size two way: though the founder microbe dividing and through other microbes joining the biofilm from the surrounding environments. The microbes that join the biofilm aren’t necessarily the same species of bacteria as the founder microbe, they might not even be bacteria but other microbes like fungi and protozoa. Some of the microbes that join biofilms do not produce exo-polysaccharides or secrete DNA and might not have the fimbriae that allow the founder colony to bind to the surface, but can easily bind to the sticky extra-cellular matrix (ECM) of the biofilm, adding to the community. The community grows in size and at this point becomes 10 to 1000 times more resistant to antibiotic treatment (Olson, ME et al, 2002) and can act as a reservoir for chronic reinfection. When the biofilm is large enough areas of the ECM are degraded with enzymes which leads to dispersal of a portion of the biofilm, allowing cells in the biofilm to spread out and establish more biofilms. |
Figure 1: Stages of Biofilm Development. This diagram is a cartoon of the 5 stages of biofilm development: initial attachment, irreversible attachment, maturation 1, maturation 2 and finally dispsersal. Under the cartoon are 5 electron micrographs showing what the biofilm looks like at each stage. Image by D. Davis form Monroe, D "Looking for Chinks in the Armor of Bacterial Biofilms" PLoS Biol, Vol 5, issue 11.
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Significance of Biofilms
Biofilms are a huge problem both medically and industrially. It has been estimated that 65% of human nosocomial infections such as Clostridium difficile are caused biofilms. This combined with the a huge increase in antibiotic resistance results in a huge cost in human life and in healthcare costs.(Olson et al, 2002)The oil industry is a prime example of the industrial significance of biofilms. Biofilm form on the surface of pipes and can potentially cause blockages. Further to this biofilms provide a niche for sulfate reducing bacteria to grow which turn sulphate rich sea-water into hydrogen sulphate. This compound is toxic, corrodes the pipes and taints oil and gas which reduces its worth causing huge financial damage. (Schwermer, CU et al, 2008)Biofilms in DISColi
Unfortuntely the available lab strains of E. coli have been selected against biofilm formation, so none of them were suitable as a chassis.
However, Pseudomonas aeruginosa is the organism most commonly used for research into biofilms. It was the obvious choice to use P. aeruginosa in the DISColi project to test the basic properties of biofilms.
Continue to P. aeruginosa
