Exopolysaccharide Yield Research Articles

Energy requirements for microbial exopolysaccharide synthesis

Calculations indicate that at the high specific rates of exopolysaccharide synthesis obtained in continuous cultures of Xanthomonas campestris and mucoid Pseudomonas aeruginosa strains the ATP demand for this synthesis is a significant proportion of total cellular ATP demand. However, depending upon the proportion of polymer substituents more oxidised than the carbohydrate substrate, some, and in certain cases all of this energy can be provided via NAD(P)H2 produced during exopolysaccharide synthesis. For xanthan production by X. campestris a P/O ratio of 2.2 to 2.6, depending on the content of pyruvyl substituents, would be necessary for energy generation as a direct result of xanthan synthesis to support the ATP demand for this synthesis. In sulphur-limited cultures of X. campestris, however, energy metabolism is shown to be inefficient, the organism exhibiting either a low P/O ratio or low YATP. In such cultures the yield of exopolysaccharide from glucose was 0.62/g glucose compared with maximum theoretical yields of 0.81 to 0.87/g glucose for P/O ratio of 1 to 3.

Biosynthesis of exopolysaccharide by Pseudomonas aeruginosa.

In batch cultures of Pseudomonas aeruginosa, the maximum rate of exopolysaccharide synthesis occurred during exponential growth. In nitrogen-limited continuous culture, the specific rate of exopolysaccharide synthesis increased from 0.27 g g of cell-1 h-1 at a dilution rate (D) of 0.05 h-1 to 0.44 g g of cells h-1 at D=0.1 H-1. The yield of exopolysaccharide on the basis of glucose used was in the range of 56 to 64%. Exopolysaccharide was also synthesized in carbon-limited cultures at 0.19 g g of cell-1 h-1 at D=0.05 h-1 in a 33% yield. Nonmucoid variants appeared after seven generations in continuous culture and rapidly increased in proportion to the total number of organisms present.