Carbohydrate metabolism in lactan gum producing rahnella aquatilis

Lactan gum produced by Rahnella aquatilis is a high viscous, anionic polysaccharide and has shear thinning behaviour. Lactan gum yield and concentration was greater on disaccharides such as lactose and sucrose than on monosaccharides such as glucose and galactose. When initial carbon source concentration was 45 g/l of sucrose or lactose, the microorganisms produced 28 g/l and 27 g/l of lactan, respectively with a yield more than 60%. β-Galactosidase, hydrolyzing lactose into galactose and glucose, was induced by lactose or galactose. When initial carbon source was 45 g/l of mixed carbon I (glucose:galactose=1:1), lactan gum concentration was higher than that from 45 g/l of monosaccharide (glucose or galactose) but was similar to the result from 45 g/l of lactose. Therefore, lactose hydrolysis reaction by β-gafactosidase does not seem to be a rate determining step in lactan gum biosynthesis. When initial carbon source was 45 g/l of mixed carbon II (glucose:fructose=1:1), total carbon source consumption rate was slower than that from sucrose, but glucose consumption rate was faster than that from fructose.