Biofilm formation

In aquatie environments, mierobial eells attaeh to solids, ineluding metals. Immobilized eells grow, reproduee, and produee extraeellular polymers. 

Modem Aspects of Electrochemistry, Number 34, edited by John O M. Bockris et al. Kluwer Academic /Plenum Publishers, New York, 2001. 

Microbial cells transported with the stream of fluid above the surface interact with conditioning films. Immediately after attachment, microorganisms initiate production of slimy adhesive substances, predominantly exopolysaccharides (EPS) that assist the formation of microcolonies and microbial films. EPS create bridges for microbial cells to the substratum and permit negatively charged bacteria to adhere to both negatively and positively charged surfaces. EPS may also control interfacial chemistry at the mineral/biofilm interface. 

Detachment includes two processes erosion and sloughing. Sloughing is a process in which large pieces of biofilm are rapidly removed, frequently exposing the surface. The causes are not well understood. Biofilm erosion is defined as continuous removal of single cells or small groups of cells from the biofilm surface and is related to shear stress at the biofilm/fluid interface. An increase in shear stress increases the erosion rate and decreases the biofilm accumulation rate. Empirical observations indicate that the erosion rate is related to biofilm thickness and density. 

Manganese and iron oxidation are coupled to cell growth and metabolism of organic carbon. Microbially deposited manganese oxide on stainless and mild steel alters electrochemical properties related to the potential for corrosion. Iron-oxidizing bacteria produce tubercles of iron oxides and hydroxides, creating oxygen-concentration cells that initiate a series of events that individually or collectively are very corrosive. 

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As discussed above, deposits can cause accelerated localized corrosion by creating differential aeration cells. This same phenomenon occurs with a biofilm. The nonuniform nature of biofilm formation creates an inherent differential, which is enhanced by the oxygen consumption of organisms in the biofilm. 

Biofilm formation Organic polymer Inorganic polymer... 

SRB, a diverse group of anaerobic bacteria isolated from a variety of environments, use sulfate in the absence of oxygen as the terminal electron acceptor in respiration. During biofilm formation, if the aerobic respiration rate within a biofilm is greater than the oxygen diffusion rate, the metal/biofilm interface can become anaerobic and provide a niche for sulfide production by SRB. The critical thickness of the biofilm required to produce anaerobie conditions depends on the availability of oxygen and the rate of respiration. The corrosion rate of iron and copper alloys in the presence of hydrogen sulfide is accelerated by the formation of iron sulfide minerals that stimulate the cathodic reaction. 

The above is true for nonbiological fluidization as well as for biofluidization. An important difference is the changing nature of solids mixing and stratification in biofluidization as a result of biofilm formation, as was discussed in Sec. 5.3. 

Sreekrishnan, T. R., Ramachandran, K. B., and Ghosh, P., Effect of Operating Variables on Biofilm Formation and Performance of an Anaerobic Fluidized-Bed Bioreactor, Biotechnol. Bioeng., 37 557 (1991)... 

Zhang K, Ou M, Wang W and Ling J. 2009. Effects of quorum sensing on cell viability in Streptococcus mutcrns biofilm formation. Biochem Biophys Res Commun 379(4) 933—938. 

Hadjiev D, Dimitrov D, Martinov M, Sire O (2007) Enhancement of the biofilm formation on polymeric supports by surface conditioning. Enz Microbial Technol 40 840-848... 

The activated carbon is often chosen as granular carrier and is referred to as granular activated carbon (GAC) or biological activated carbon (BAC). This support is characterized by a strong propensity to adsorb the dyes and is a good candidate for biofilm formation, because of its natural organic matrix. The marked propensity to adsorb dyes contributes to increase the tolerance to shock loadings. In fact, under transient conditions the free surface of the AC acts as a temporary buffer for the dye, which is eventually released as dye disappears. 

This is the major factor contributing to the accumulation of a high number of attached cells. After biofilm formation the biomass growth depends mostly on the medium content and might be as quick as the growth rate of microorganisms. 

Lateral transfer of ionic species through the biointerphasial double layer has only recently received attention. Yet it is a subject of significant relevance, because it may play a crucial role in the interactions of organisms with their surroundings, for example in bacterial adhesion processes, biofilm formation (and removal), etc. 

H 0 A-butanoyl-L-homoserine lactone, BHL or C4-HSL Aeromomas hydrophila Aeromonas salmonicida Pseudomonas aeruginosa, Serratia liquefaciens Extracellular protease, biofilm formation. Extracellular protease. Virulence factors - alkaline protease, cyanide, elastase, haemolysin, lectins, pyocyanin, rhaminolipid, RpoS Swarming, protease. 

A r-(3-oxododccanoyl)-L-homoscrinc lactone, OdDHL or 30, C12-HSL Pseudomonas aeruginosa Virulence factors - alkaline protease, clatasc, exotoxin A, haemolysin, neuraminidase, exoenzyme S, Xcp secretion, RhlR, biofilm formation. 

Boddicker, J. D., Ledeboer, N. A., Jagnow, J., Jones, B. D., and Clegg, S. (2002). Differential binding to and biofilm formation on, HEp-2 cells by Salmonella enterica serovar... 

The yield (y) of a biomass production process is defined as the moles of biomass formed per mole of substrate consumed. Aerobic conditions are more conducive to higher biomass formation (and therefore also to biofilm formation) than anaerobic conditions. Empirically, under aerobic conditions, a yield of 0.05 - 0.6mol biomass/mol carbon can be obtained, while under anaerobic conditions the attainable yield falls to 0.04 -0.083mol. The reaction kinetics of biodegradation processes can be approximated by the first-order reaction rate constant k as follows ... 

McCoy WE, Bryers JD, Robbins J, Costerton JWC. 1981. Observations on biofilm formation. Can J Microbio 27 910-17. 

Flocculins and especially Flo 11 are responsible for morphogenic phenomena such as pseudohyphal growth and biofilm formation in yeast. Biofilm formation is an adhesive phenomenon akin to flocculation. The majority of bacteria exist in highly organized natural biofilm populations rather than in free floating cultures. Within the biofilm, bacteria display coordinated behavior. They form structures, release toxins or emit light. They, sometimes, differentiate to form physiologically defined... 

Verstrepen KJ, Klis FM, Flocculation, adhesion and biofilm formation in yeasts, Mol Microbiol 60 5-15, 2006. 

Reynolds TB, Fink GR, Baker s yeast, a model for fungal biofilm formation,... 

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