Microbial Exopolysaccharide Synthesis

The fate of a carbohydrate (or other) substrate supplied to an exopolysaccharide-producing microbial cell depends on the microbial species chosen. As most results have been obtained from bacterial species, this review will be concerned essentially with the synthesis of exopolysaccharides by bacteria. In some bacteria, given the correct substrate, exopolysaccharide may be formed without penetration of the cell membrane by the substrate. This is seen in dextran and levan-forming cells supplied with sucrose or several of its analogues. Examples are to be found in Leuconostoc mesenterioides, Streptococcus or Bacillus species. Although this process has been studied by various workers, (1,2) the polysaccharides formed are more limited in their applications and current interest is centred rather on species which form their polymer intracellularly then excrete it into the medium. The aim is therefore to consider a series of processes by which substrates enter the microbial cells, are modified by a series of