Summary: Exopolysaccharide-synthesizing variants of NCIB 10541 were isolated on media containing carbenicillin. The exopolysaccharide was identified as alginic acid with a mannuronic acid:guluronic acid ratio of 1:2. These strains lost the ability to produce alginate at a high frequency, but more stable mutants which produced increased amounts of polysaccharide could be isolated by subsequent mutagenesis. High concentrations of polysaccharide (approximately 20 g 1) were obtained in nitrogen-limited continuous culture with a minimal glucose medium. In common with other bacterial alginates, the polymer is acetylated and has similar rheological properties to alginate from brown algae. An alginate lyase activity was present in cultures at sufficient specific activities to result in a low molecular weight, low viscosity polymer with rheology similar to printing grade alginate. This degradation was overcome by incorporation of a proteolytic enzyme into the growth medium without adverse effects on bacterial or polysaccharide yields. As an organism for the study of alginate biosynthesis. possesses advantages over or in terms of yield, strain stability, and absence of known pathogenicity.


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