ABSTRACT
Many polysaccharides from aerobic bacterial species, yeasts, and microalgae have now been analyzed and, in a large number of examples, have been fully characterized structurally. Only strictly anaerobic bacteria have received little attention, although even some of the EPS among these have been fully studied. In some bacterial genera, a wide range of chemotypes and serotypes is found and this is typified by genera of the Enterobacteriaceae such as Escherichia or Klebsiella/Enterobacter species. It is also a characteristic of the gram-positive species Streptococcus pneumoniae. The result for these three groups of bacteria is that each produces a range of almost 100 chemotypes and serotypes. In other types of bacteria, a much more restricted range of chemotypes or even one polysaccharide structure only may be found. Thus, almost all Xanthomonas isolates produce xanthan (albeit varying in its acylation, vide infra), whereas all Azotobacter vinelandii strains synthesize a form of bacterial alginate. Similarly, colanic acid production is widespread among certain members of the Enterobacteriaceae [1], although it may only be expressed under conditions such as reduced incubation temperature, high salt concentrations, or other forms of nutritional stress. It should also be remembered that some bacterial genera seldom yield polysaccharide-producing species. Thus, few gram-positive Bacillus spp. produce EPS. An exception is Bacillus circulans, which has yielded a number of EPS-synthesizing isolates. One of these proved to have hexasaccharide repeat unit (Fig. 1) [2].
