Stock cultures of Xanthomonas campestris NRRL B-1459 require special attention to maintenance and propagation to assure consistent production in good yields of the extracellular polysaccharide xanthan. Under customary conditions of propagative maintenance on agar slants, variant colony types develop that are smaller in size than the normal type. The rate of regression of the normal to the variant forms was diminished when the D-glucose content of the stock medium was sufficient to avoid depletion during storage and when transfer to fresh medium was reduced to 14-day intervals. Under conditions for polysaccharide production, the normal large-colony type gives crude culture liquors after 48 h of 7000 centipoise (cp) viscosity; the predominant variant form gives only 4000 cp. On the basis of 2.1% initial D-glucose, biopolymer yields for the normal and variant strains were 62 and 43%, respectively. Polysaccharide produced by the variant (small-colony type) differs adversely in solution properties from that of the parent strain (large-colony type); it differs also in its lower content of pyruvic acid and O-acetyl substituents. The molar ratios of constituent sugars (D-glucose, D-mannose, and D-glucuronic acid), however, were identical in polysaccharides with the normal and variant strains. Exclusion of colonial variants from fermentations is prerequisite to production of xanthan optimum in properties and yield.

Industrially important polysaccharides are now primarily obtained from plant sources. One exception is the exocellular bacterial polysaccharide, dextran. A survey at the Northern Laboratory revealed that many other microbial polysaccharides could be synthesized by the action of micro‐organisms on starch‐derived saccharides. Previous publications from this laboratory describe the production of the microbial polymer, phosphomannan, synthesized by the yeast Hansenula holstii. This paper describes the production of another polysaccharide, synthesized by the bacterium Xanthomonas campestris NRRL B‐1459. Fermentation of media containing 3 per cent dextrose, seeded with 5 per cent inoculum of X. campestris NRRL B‐1459 and cultured aerobically at 28°C, is complete in 96 h. A light tan polymer is recovered in yields of 50 per cent, based on commercial dextrose, from the viscous fermentation broth by precipitation with methanol in the presence of an electrolyte. The viscosities of aqueous re‐solutions containing 1 and 2 per cent of the polymer were 3,000 cP and 11,000 cP respectively.

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