A new species of Pseudomonas was isolated that produced copious amounts of an exocellular heteropolysaccharide (PS-60) after incubation for 3 days at 30°C in media containing 3% glucose as a carbon source. The polysaccharide was composed of approximately 46% glucose and 30% rhamnose and, in addition, contained 21% uronic acid and 3% O-acetyl. Upon deacetylation by a mild alkaline treatment, PS-60 produced a brittle, firm, and optically clear gel. This gelling property was thermoreversible. The PS-60 gel exhibited excellent heat stability that withstood autoclaving (i.e., 121°C for 15 min) for several cycles. The gel strength, melting point, and setting point of the polysaccharide were controlled primarily by the concentration of cations. PS-60 was not affected by a variety of enzymes. The results of tests involving various culture media and biochemical test media indicate that PS-60 is an excellent alternative gelling agent to agar.

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An exocellular bacterial polysaccharide called "xanthan gum" that was originally developed by the Peoria Lab of the USDA nearly two decades ago is at this time the only bacterial heteropolysaccharide that is being produced on a large commercial scale. The commercial success of xanthan gum is attributed to its many valuable and often unique properties for industrial applications and to an economic manufacturing process.Among our novel polysaccharides that are produced by many bacterial species that we have isolated in our screening program, a product which is now trade named ZANFLO is especially outstand ing in its fermentation efficiency and product properties.ZANFLO is produced by a bacterium that was isolated from a soil sample taken at Tahiti. The organism is a gram-negative, non -sporeforming rod with a size range of 0.75-1.0 by 1-2μ. The dimensions change during the fermentation. At the beginning of the fermentation they are large rods which quickly change to a coccobacillus 0.75-1.0μ in diameter. It is heavily encapsulated. Some of its biochemical characteristics are shown in Table I. This organism produces a positive lactose reaction within 24 hours. It possesses nitrate reductase, CMCase, urease and lysine decarboxylase. It can utilize citrate as a sole carbon source and will grow in the presence of 8% NaCl. Its optimum growth temperature is 30-33°C. and growth will occur at 45° C. In litmus milk this organism produces an acid curd with peptoniza tion and reduction of the litmus. At the present time we are evaluating these and other significant taxonomic tests to ascer tain the identity of this microorganism. This organism is quite specific about what carbon source it will use for optimum polysaccharide production. It produces an excessive amount of acid with glucose as a carbon source with only minimum polysaccharide synthesis. Even with pH control the conversion efficiency with glucose is still very low. Poly saccharide synthesis is better with sucrose or maltose or mixtures of these than with glucose, but the conversion efficiency is still poor. Improved polysaccharide synthesis is found with 211 Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 27, 2016 |