Microbial biofilms

Structure of biofilms, microbial composition of heterogeneous granular biofilms and detection of bacteria, ciliates, and fungi in and on granules -b [i64] jjr O o iz ... 

West ALL, F. Rince, Y. (1994) Biofilms, microbial mats, and microbe-particle interactions electron microscope observations from diatomaceous sediments. Sedimentology, 41, 147-162. 

Diversity of biofilm microbial communities was assessed by restriction analyses of PCR-amplified rDNA (16S-8V/16S-1387R, lenght 1352 bp). PCR products were restriction digested with HinfI (G ANTC) and HaeIII (GG CC) enzymes (Boehringer-Mannheim) in accordance with the manufacturer s instructions. 

Hamilton, W.A., 1987, Biofilms microbial interactions and metabolic activities. Symp. Soc. Gen. Microbiol. 41, 361 - 385. 

Donlan R. Biofilms microbial life on surfaces. Emerg Infect Dis 2002 8 881-890. 

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. 

Recently, there has developed a greater recognition of the complexity of the MIC process. MIC is rarely hnked to a unique mechanism or to a single species of microorganisms. At the present state of knowledge, it is widely accepted that the growth of different microbial species within adherent biofilms facihtates the development of structured consortia that may enhance the microbial effects on corrosion. 

The cells activities have been described based on a multi-species biofilm model, and the microbial kinetics by a mathematical model. Using this model predicts that the biomass on the external surface of the biofilm has higher activity than the biomass near the solid support surface, and that condition may occur, after the biofilm has reached a critical dept or formed... 

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... 

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. 

Sarand I, S Timonen, E-L Nurmiaho-Lassila, T Koivula, K Haatela, M Romantschuk, R Sen (1998) Microbial biofilms and catabolic plasmid harbouring degradative fluorescent pseudomonads in Scots pine mycor-rhizospheres developed on petroleum contaminated soil. FEMS Microbiol Ecol 27 115-126. 

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... 

N. J. E. Dowling, J. Guezennec, and D. C. White. Facilitation of corrosion of stainless steel exposed to aerobic seawater by microbial biofilms containing both facultative and absolute anaerobes. In Proceedings Volume. Inst Petrol Microbiol Comm Microbial Problems in the Offshore Oil Ind Int Conf (Aberdeen, Scotland, 4/15-4/17), 1986. 

H. A. Videla, P. S. Guiamet, O. R. Pardini, E. Echarte, D. Trujillo, and M. M. S. Freitas. Monitoring biofilms and MIC (microbially induced corrosion) in an oilfield water injection system. In Proceedings Volume. Annu NACE Corrosion Conf (Corrosion 91) (Cincinnati, OH, 3/11-3/15), 1991. 

Jones B (1995) Processes associated with microbial biofilms in the twilight zone of caves examples from the Cayman Islands. J Sediment Res A65 552-560... 

Physical methods for the control of microbial biofilms, although often effective, are in many situations impractical. In this context it is notable that an almost universal feature of the biofilm mode of growth is their profound resistance to antibacterial compounds. Conventional chemical control methods, developed for use against fastgrowing planktonic cultures are only poorly effective against biofilm bacteria. Large doses of biocide or antibiotics, which are either environmentally undesirable or above toxic thresholds respectively, are required to eradicate biofilms in industry and medicine. 

Lower chemical reactivity with non-target molecules is useful for another performance-related reason. Microorganisms prefer the protection and luxuriant environment in biofilms (the adherent microbial communities that cause detrimental surface-fouling effects in water cooling systems). Most (>99%) of the viable microorganisms in industrial systems are found in biofilms, not floating around freely in the bulk recirculating water. Compared to unstabilized chlorine or bromine, STABREX more effectively removes and disinfects biofilms as shown in Table 6. 

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