Xanthan production by a novel mutant strain of Xanthomonas campestris: Application of statistical design for optimization of process parameters

Xanthan gum is a microbial polysaccharide of great commercial importance as it has unusual rheological properties in solution and consequent range of applications. In this study, a series of mutants were isolated from Xanthomonas campestris by acridine orange mutagenesis. The gum yield of XC5 mutant was 15.6% better than that of the parent strain. Sequential methodology based on the application of two types of experimental designs was used to optimize the fermentation conditions for xanthan production from X. campestris strain XC5 in shaking flask cultures using beet molasses as the sole substrate. Using Plackett-Burman design, beet molasses and KH2PO4 were identified as significant variables which highly influenced xanthan gum production and these variables were subsequently optimized using a steepest ascent design. The steepest ascent method was demonstrated effectively and efficiently to approach the neighborhood of the optimum. The optimum medium composition was found to be: Beet molasses, 100; KH2PO4, 10; MgCl2 center dot 6H(2)O, 0.3; citric acid, 0.5; CaCl2 center dot 2H(2)O, 0.006; NH4Cl, 0.2. Xanthan production increased markedly from 11.5 to 28g/l, when XC5 strain was cultivated in the optimal medium, compared to the basal.