Isolation of a novel mutated strain of Xanthomonas campestris for xanthan production using whey as the sole substrate

Xanthomonas campestris produces a water- soluble extracellular polysaccharide, xanthan gum, which is extensively applied in food and other industries. This bacterium is not able to utilize lactose due to low levels of - galactosidase activity or absence of the enzyme. Consequently very little xanthan is produced when the bacterium grows in lactose- based media such as whey. Whey poses a major waste disposal problem due to its high BOD. Therefore, this waste is a suitable substrate for conducting fermentation processes. In this study, a mutant strain was isolated from a plenty of Xanthomonas campestris cells exposed to nitrous acid mutagenesis (NA1). Environmental conditions were optimized and maximum activity of the -galactosidase enzyme obtained at pH 5.5 and 38C. Also, the -galactosidase activity in NA1 cultures was increased 9.5 folds, comparing to that of the wild type cultures (336.1 U vs. 35.4 U). Xanthan gum production by NA1 using whey as carbon source was also studied. By using experimental design (Plackett-Burman) and statistical analysis, among seven parameters tested, we found that whey, as the main substrate, and pH were the first factors affecting gum production. Gum production using significant factors was carried out in a lab-scale fermentor and 10 g l-1 xanthan was obtained.