Exopolymers

Biocorrosion of stainless steel is caused by exopolymer-producing bacteria. It can be shown that Fe is accumulated in the biofilm [2.62]. The effect of bacteria on the corrosion behavior of the Mo metal surface has also been investigated by XPS [2.63]. These last two investigations indicate a new field of research in which XPS can be employed successfully. XPS has also been used to study the corrosion of glasses [2.64], of polymer coatings on steel [2.65], of tooth-filling materials [2.66], and to investigate the role of surface hydroxyls of oxide films on metal [2.67] or other passive films. 

In order to understand current approaches for prevention and control of biofilms, we must first consider the reasons for the failure of conventional antimicrobial protocols. There are thought to be three main reasons as to why biofilm bacteria out-survive their planktonic counterparts during antimicrobial treatments (reviewed by McBain et a/.16).These are i) poor penetration of antimicrobial compounds due to the presence and turn-over of exopolymer slime (glycocalyx) ii) the imposition of extreme nutrient limitation within the depths of the biofilm community and the co-incident expression of metabolically-dormant, recalcitrant phenotypes and (iii) the expression of attachment-specific phenotypes that are radically different and intrinsically less susceptible than unattached ones. 

Jahn, A. and P.H. Nielsen (1998), Cell biomass and exopolymer composition in sewer biofilms, Water Sci. Tech., 37(1), 17-24. 

In a laboratory study by Schlekat et al. [15], it was demonstrated that coating silica particles with an exopolymer prepared from an estuarine bacterium enhanced the sorption of cadmium on to the particles. The composition of the exopolymer was glucose, galactose and glucuronic acid in the ratio 5 2 1. These investigations also compared the effects of salinity, pH and different concentrations of cadmium. Increasing salinity resulted in less cadmium associated with the particles, presumably due to competition with the chloride ion. The pH had a dramatic effect, resulting in only ca. 10% absorbed at pH 5 to more than 95% at pH 9. 

Geesy, G. G., Bremer, P. J., Smith, J. J., Muegge, M. and Jang, L. K. (1992). Two-phase model for describing the interactions between copper ions and exopolymers from Alteromonas atlantica, Can. J. Microbiol., 38, 785-793. 

Transparent exopolymer particles (TEPs) Detrital particulate organic matter whose origin is secretions and exudates from marine organisms. 

Similarly, bioemulsifiers, such as emulsan produced by Acinetobacter calcoaceticus, have been shown to aid in removal of metals. Potential for remediation of soils using bacterial exopolymers is indicated by a study which showed that purified exopolymers from 13 bacterial isolates removed cadmium and lead from an aquifer sand with efficiencies ranging from 12 to 91% (Chen et al., 1995). Although such molecules have much larger molecular weights ( 106) than biosurfactants, this study showed that sorption by the aquifer sand was low, suggesting that in a porous medium with a sufficiently. large mean pore size, use of exopolymers may be feasible. 

Few studies have evaluated the potential for use of microorganisms in the remediation of sea water however, the problems encountered are similar to those of other aquatic systems. Stupakova et al. (1988) proposed the use of the marine bacteria Deleya venustus and Moraxella sp. for copper uptake from sea water. Additionally, Corpe (1975) performed metal-binding studies with copper using exopolymer from film-producing marine bacteria and found that insoluble copper precipitates formed, effectively decreasing copper toxicity. 

Wolfaardt, G. M., J. R. Lawrence, R. D. Robarts, and D. E. Caldwell. 1998. In situ characterization of biofilm exopolymers involved in the accumulation of chlorinated organics. 

A biofilm is commonly visualized as a two-dimensional matrix layered on a solid surface. However, aggregates of exopolymer, detritus, and cells also form in the water column through a variety of physical, chemical, and biotic processes (Ward et al., 1994 Grossart et al., 1997 Chapter 12). These aggregates are variously described as floes or snow . A type of aggregate... 

Decho, A. W. 1990. Microbial exopolymer secretions in ocean environments their role(s) in food webs and marine processes. Oceanography and Marine Biology Annual Review 28 73-153. 

Passow, U., and A. L. Alldredge. 1994. Distribution, size and bacterial colonization of transparent exopolymer particles (TEP) in the ocean. Marine Ecology Progress Series 113 185-198. 

Zhou, J., K. Mopper, and U. Passow. 1998. The role of surface-active carbohydrates in the formation of transparent exopolymer particles by bubble adsorption of seawater. Limnology and Oceanography 43 1860-1871. 

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