Biofilms production

Bacterial resistance to biocides (Table 13.2) is usually considered as being of two types (a) intrinsic (innate, natural), a natural property of an organism, or (b) acquired, either by chromosomal mutation or by the acquisition of plasmids or transposons. Intrinsic resistance to biocides is usually demonstrated by Gram-negative bacteria, mycobacteria and bacterial spores whereas acquired resistance can result by mutation or, more frequently, by the acquisition of genetic elements, e.g. plasmid- (or transposon-) mediated resistance to mercury compounds. Intrinsic resistance may also be exemplified by physiological (phenotypic) adaptation, a classical example of which is biofilm production. 

Biofilm production Phenotypic adaptation Plasmid transfer may occur within biofilms... 

Croxatto A, Chalker VJ, Lauritz J, Jass J, Hardman A, Williams P, Camara M and Milton DL. 2002. VanT, a homologue of Vibrio harveyi LuxR, regulates serine, metalloprotease, pigment, and biofilm production in Vibrio anguillarum. J Bacteriol 184 1617—1629. 

Eriksson, M., Dalhammar, G. and Mohn, W. W. (2002). Bacterial growth and biofilm production on pyrene, FEMS Microbiol. Ecol., 40, 21-27. 

Jeon CO, Park W, Padmanabhan P, DeRito C, Snape JR, Madsen EL (2003) Discovery of a bacterium with distinctive dioxygenase, that is responsible for in situ biodegradation in contaminated sediment. Proc Natl Acad Sci USA 100 13591-13596 Eriksson M, Dalhammer G, Mohn WW (2002) Bacterial growth and biofilm production on pyrene. FEMS Microbiol Ecol 40 21-27... 

Joseph, C. M. L., Kumar, G., Su, E., Bisson, L. F. (2007). Adhesion and biofilm production by wine isolates of Brettanomyces bruxellensis. American Journal of Etiology Viticulture, 58, 373-378. 

Intrinsic resistance is the most common form of resistance to biocides and is considered to involve exclusion of a biocide as a consequence of impermeability. Additionally, physiological adaptations of an organism in response to changes in the growth environment can modulate sensitivity to biocides, a classical example of which is biofilm production [236]. 

System Material Organisms Age of biofilm Product Contact time Concentration Reduction in viable cell counts Detachment of biofilms References... 

Table 13 shows some of the developmental products that have EPA appHcations pending and may be available in the near future. Sea Nine is a variation on the very successflil isothiazolone chemistry. It is claimed to be an improvement over metallic actives used for antifouling paint and wood preservation (46,47). Decylthioethylamine and its water-soluble hydrochloride are claimed to be especially effective at controlling biofilm in cooling water appHcations (48—50). The hydroxymethylpyra2ole shown is also suggested to have properties that are well suited to the protection of aqueous products or emulsions (51,52). 

Many of the by-products of microbial metaboHsm, including organic acids and hydrogen sulfide, are corrosive. These materials can concentrate in the biofilm, causing accelerated metal attack. Corrosion tends to be self-limiting due to the buildup of corrosion reaction products. However, microbes can absorb some of these materials in their metaboHsm, thereby removing them from the anodic or cathodic site. The removal of reaction products, termed depolari tion stimulates further corrosion. Figure 10 shows a typical result of microbial corrosion. The surface exhibits scattered areas of localized corrosion, unrelated to flow pattern. The corrosion appears to spread in a somewhat circular pattern from the site of initial colonization. 

Biofilms can promote corrosion of fouled metal surfaces in a variety of ways. This is referred to as microbiaHy influenced corrosion. Microbes act as biological catalysts promoting conventional corrosion mechanisms the simple, passive presence of the biological deposit prevents corrosion inhibitors from reaching and passivating the fouled surface microbial reactions can accelerate ongoing corrosion reactions and microbial by-products can be directly aggressive to the metal. 

Use of biofilm reactors for ethanol production has been investigated to improve the economics and performance of fermentation processes.8 Immobilisation of microbial cells for fermentation has been developed to eliminate inhibition caused by high concentrations of substrate and product, also to enhance productivity and yield of ethanol. Recent work on ethanol production in an immobilised cell reactor (ICR) showed that production of ethanol using Zymomonas mobilis was doubled.9 The immobilised recombinant Z. mobilis was also successfully used with high concentrations of sugar (12%-15%).10... 

Apart from nutrient limitation and diminished growth rates, another reason for this decreased susceptibility is the prevention of access of a biocide to the underlying cells. Thus, in this mechanism, the glycocalyx as well the rate of growth of the biofilm micro-eolony in relation to the diffusion rate of the biocide across the biofilm, can affect susceptibility. A possible third mechanism involves the increased production of degra-dative enzymes by attached cells, but the importance of this has yet to be determined. 

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. 

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. 

MIC depends on the complex structure of corrosion products and passive films on metal surfaces as well as on the structure of the biofilm. Unfortunately, electrochemical methods have sometimes been used in complex electrolytes, such as microbiological culture media, where the characteristics and properties of passive films and MIC deposits are quite active and not fully understood. It must be kept in mind that microbial colonization of passive metals can drastically change their resistance to film breakdown by causing localized changes in the type, concentration, and thickness of anions, pH, oxygen gradients, and inhibitor levels at the metal surface during the course of a... 

When biofilms are formed on metallic surfaces, they can seriously corrode performance oil production facilities, chemical processing plants, paper mills, ships, and water distribution networks. Microbiologically influenced corrosion (MIC) represents the most serious form of that degradation. 

H2S production caused by the growth of sulfate-reducing bacteria in a biofilm in the reservoir rock close to the injection well (biofilm model)... 

The development of these biofilms within the system and on the wire can lead to major production problems due to these being transferred onto the paper sheets. Once these are an integral part of the sheet, the drying stage causes shrinkage and holes or tears can occur. This causes considerable down time and loss of income. 

The new antimicrobial is an order of magnitude less toxic, several orders of magnitude less volatile, easier to handle, more compatible with other water treatment chemicals, more effective against biofilms, and it generates less than half the disinfection by-products compared to chlorine or other alternatives. One hundred fifty billion gallons of industrial water have by now been successfully treated globally. Use of this new antimicrobial has substantially reduced environmental and human health risks from industrial water treatment by replacing nearly thirty million pounds of chlorine. The new product is proven to comparatively perform better, more safely, and it is substantially easier to apply than chlorine. 

The new stabilized bromine antimicrobial is an excellent antimicrobial having been proven superior in field and laboratory experiments compared to chlorine, stabilized chlorine, and equal to or better than solid hypobromite antimicrobials. The product is effective for the control of microbial biofilms and highly diverse microbial communities, including those that harbor Legionella. 

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