Bacteria cell-surface polysaccharides

Gram-negative bacteria have a more complex cell surface. The peptidoglycan layer is also the outer layer with respect to the cytoplasmic membrane. However, besides this, they have another outer polysaccharide membrane. This outer membrane is built out of lipopolysac-charides and lipoproteins, and can be a serious barrier for permeating hydrophilic molecules. 

Attachment of bacteria. At low ionic strength of the medium — as in many freshwaters — bacteria-surface interactions are controlled by the effects of van der Waals attraction and electrostatic repulsion. At high ionic strength — as in seawater — steric interactions between the outer cell surface macromolecules and the substratum gain in importance (van Loosdrecht et al., 1989 Rijnaarts etal., 1999). Additionally, flagellar and twitching motility of bacteria was found to be essential in the process of attachment by bacteria onto surfaces (Pratt and Kolter, 1998 O Toole and Kolter, 1998). It seems that extracellular polysaccharides of bacteria are not involved in the adhesion process itself. However, bacterial extracellular polysaccharides are necessary for the development of a biofilm and for the formation of microcolonies (Allison and Sutherland, 1987 Hoyle et al., 1993). 

The interaction between aroma compounds and other wine micro-organisms (e.g. lactic acid bacteria) or with metabolites produced during malolactic fermentation has been studied to a limited extent. Interactions between polysaccharides produced by the most common wine lactic bacteria (Oenoccocus oeni) during malolactic fermentation have been shown to be responsible for the reduced volatility of some aroma compounds in wines (Boido et al. 2002). The possibility of direct interactions between the surface of the bacteria cells and aroma compounds should also be considered since this type of interaction has been found for other food lactic bacteria (Ly et al. 2008). 

Sialic acids are a family of nonulosonic acids that have been predominantly found as the outermost carbohydrate units on glycoproteins and glycolipids of vertebrates, or as components of polysaccharides in certain types of bacteria (I, 2). Sialic acids play vital roles in a variety of physiological and pathological processes in vertebrates, such as cellular recognition and communication (1, 2). They are also believed to be important virulence factors in bacteria, used by bacteria to mimic sialylated host cell surface carbohydrate structures to evade detection and attacking by the immune defense mechanisms of the host (3-6). 

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