Polysaccharide extracellular , bacterial

Several glyculosonic acids have been identified as components of bacterial polysaccharides. D-/yxo-Hexulosonic acid, as Q -D-pyranosyl residues (23), is a component of the extracellular polysaccharide from a Rhodococcus species. The LPS from Acinetobacter calcoaceticus NCTC 10305 contains - D-g/ycero-D-/a/o-octulosonic acid (24). It is isosteric with 3-deoxy-D-mnnno-octulosonic acid (25), which is a constituent of bacterial LPS and links the polysaccharide part to the lipid A region. It seems possible that D-g/ycero-D-tfl/o-octulosonic acid replaces 3-deoxy-D-/wan o-octulosonic acid in the A. calcoaceticus LPS. 

Several natural polysaccharides are esterified with sulfuric or phosphoric acid. Sulfated bacterial polysaccharides are not, however, very common. One example is a polysaccharide from an Arthrobacter species, which is most probably linked to the proteoglycan and contains sulfated D-galactopy-ranosyl residues. An extracellular polysaccharide from a Phormidium spe-... 

The extracellular polysaccharides of Rhizobium meliloti 201 have been examined by using enzymic degradation and chemical procedures.314 A mixture of polysaccharides produced by the bacterium, when incubated with a bacterial enzyme that hydrolyzed one of these, gave oligosaccharides that could be separated by DEAE-cellulose chromatography. The major fraction was a pentasaccharide, for which methylation analysis and Smith... 

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 extracellular polysaccharides produced by bacteria are believed to be composed of acidic and neutral sugars. Gum arabic and alginic acid were selected to simulate a bacterial glycocalyx. Gum arabic is composed of... 

Bacterial exopolysaccharides (extracellular polysaccharides) include those that are made from sucrose, viz., dextrans and fructans. Dextrans are branched a-glucans containing (1 3) and/or (1 6) and occasionally (1 2) linkages. Fructans contain -D-fructofuranosyl units linked (2 6) or (2 1). 

Capsular and extracellular polysaccharides are involved in several aspects of cellular behavior that are tied to bacterial survival and virulence [321]. The capsule layer provides a physical barrier that prevents the bacteria from drying out, aiding in survival outside a host. CPS are also involved in colonization and biofilm formation. In some bacteria CPS promote adherence to surfaces, aiding colonization and biofilm formation, while CPS in other bacteria inhibit adhesion and biofilm formation [344]. 

Membrane autopsy of desalination RO membranes that had been in service for 2.5 yr in Saudi Arabia revealed bacterial deposits that are slimy and very adherent (64). This is primarily due to accumulation of extracellular polysaccharides excreted by microorganisms, thus resulting in biofilm formation (54). Bacteria embedded in a biofilm are found to be more resistant to biocides than freely suspended ones (65). 

Despite the experimental difficulties in deducing them, the sequences of a very large number of heteropolysaccharides are known from many sources. An area particularly fertile in novel structures is that of the bacterial glycocalyx, the extracellular polysaccharides and lipopolysaccharides on the outside of bacteria, which is under biological selection pressure to be as diverse as possible and thus resist attempts by the bacterium s competitors to dissolve away its protective coat with various enzymes. Those heteropolysaccharides for which there is some information on the relation between structure and properties are, unsurprisingly, those which are important to the human body or have industrial applications, and only these will be covered here. 

N. Ravenscroft, S. G. Walker, G. G. Dutton, and J. Smit, Identification, isolation, and structural studies of extracellular polysaccharides produced by Caulobacter crescentus, J. Bacterial., 173 (1991)5677-5684. 

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