A streptomycin-resistant variant of Xanthomonas campestris was grown in defined nutrientdeficient media in both batch and continuous culture. The production, composition and viscosity of the extracellular polysaccharide (xanthan) synthesized by this strain were influenced by the fermentation time and nutrient exhaustion in batch culture and by the dilution rate in continuous culture. The specific rate of exopolysaccharide synthesis was maximal during exponential growth in all of the nutrient-deficient media studied although some xanthan was formed during stationary phase. The concentration of exopolysaccharide decreased at later stages of stationary phase in some cultures. Both the extent of acylation and the consistency index of xanthan isolates were low or minimal during exponential growth, maximal in polysaccharide isolated as the growth rate fell and usually lower after this time. Between dilution rates of 0.03 and 0.06 h-' in chemostat culture, the cell and exopolysaccharide dry weights were independent of dilution rate, the specific rate of xanthan synthesis decreasing at lower growth rates. Although the variation in the acyl content and consistency index was less than that observed in batch culture, exopolysaccharide isolated at higher dilution rates tended to have a higher acetyl content, lower pyruvyl content and lower consistency index.
A mutant of Xanthomas campestris produces good yields of an exopolysaccharide. This material differs from the wild‐type xanthan from the parent bacteria, in its very low content of acetate and pyruvate and in its molar ratio of D‐glucose:D‐mannose of 2:1. Analysis of the products from xanthan lyase indicates that most of the side‐chains are disaccharides rather than the normal trisaccharides. The polymer has lower viscosity than normal xanthan. The consistency index was 20 mPa.s compared with 78 mPa.s for the product of the parent strain under standard conditions. The polysaccharide could be further modified by prolonged treatment with β‐glucuronidase, which removed some of the terminal β‐D‐glucuronosyl residues. This enzyme‐modified product had much higher viscosity than that from the mutant.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.