Improved production of rhamnolipids by a Pseudomonas aeruginosa mutant

A Pseudomonas aeruginosa mutant derived by random mutagenesis with N-methyl-N -nitro-N-nitrosoguanidine, producing high levels of the rhamnolipid biosurfactants was selected on Siegmund-Wagner [SW] plates. The mutant designated P. aeruginosa PTCC1637 produces rhamnolipids at concentrations 10 time more than parent strain. NMR analysis and surface tension measurement showed that the biosurfactants produced by the mutant were identical to those produced by the wildtype strain. The biosurfactants exhibited a low surface tension of 28.0 mN m-1 and a low critical micelle concentration of 9 mg l-1. Similar to the wildtype strain, the mutant produced biosurfactants at the stationary phase

Mutageneisis of xanthomonas campestris and selection of strains with enhanced xanthan production

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 PTCC 1473 by ethyl methanesulfonate mutagenesis. The polysaccharide yield of one mutant, XC1473E2, was 30% better than that of the parent strain. It also showed higher xanthan formation and glucose consumption rates compared to the parent strain. Xanthan produced by the mutant had enhanced viscosity, higher pseudoplasticity and larger molecular weight. Since mutant XC1473E2 appeared white on agar plates, it underwent pigment extraction with methanol. Contrary to the parent strain, the mutant showed no absorption at 443nm, i.e. the wavelength related to yellow pigment. This finding suggested that yellow pigmentation and normal xanthan biosynthesis are not necessarily concurrent. In general, mutant XC1473E2 seems to be a strain with interesting characteristics for use in commercial production of xanthan