Formation of exopolysaccharide by an orange pigmented bacterium

Exopolysaccharide production by a coryneform bacterium isolated from sorghum cane juice was studied in batch cultures, in shaken flasks and a two-liter fermentor. A solution of whey, a by-product of the cheese industry, was a suitable medium for gum production after heat treatment to remove the bulk of the proteins. Low nitrogen, high carbon levels, obtained with 1.5% whey solids supplemented with 2% lactose, favor polysaccharide production. The optimum pH for gum production was 6.5 and the optimum temperature was 30°c. Ferrous and magnesium ions were essential for a high yield of the polymer. The organism used lactose as efficiently as any carbohydrate as a carbon source for the synthesis of polysaccharide. Good aeration and mixing of the fermentation liquid were critical variables. The optimum air volume in the fermentor was the passage of l090 ml/min.

Polysaccharide formation started late in the exponential growth phase and continued after growth had ceased. The pH of the medium was maintained naturally at 7.0 ± 0.3 after the polysaccharide made its appearance. The gum was recovered by precipitation with acetone in the presence of salt. The monosaccharide constituents of the polysaccharide as determined by thin layer chromatography were galactose, mannose and rhamnose.

Morphological and physiological studies place the organism in the "Coryneform Group" and identify it as a member of the non-pathogenic group of Corynebacterium, although cell wall analysis suggested a relationship with the Arthrobacter spp. or the non-pathogenic Corynebacterium spp. Analysis of cell wall hydrolysate by two dimensional chromatography and the amino acid analyzer yielded glycine, alanine, glutamic acid, and lysine as the major amino acids and galactosamine and muramic acid as the amino sugars. The sugar components of the cell wall were galactose and glucose.