Two mutants of which over-produced extracellular polysaccharide when grown on sucrose-containing medium were isolated after mutagenesis of strain Challis with ethyl methanesulphonate. The mutants, designated strains OB20 and OB30, expressed 2.6-fold and 4.7-fold respectively more glucosyltransferase (GTF) activities than the wild-type strain. Transformation experiments suggested that the two mutants carried different mutations, denoted and . A double mutant () was constructed and this strain produced 6.4-fold more GTF. Enzymes from wild-type and mutant strains were biochemically indistinguishable and they synthesized structurally identical glucans. Increasing the Na concentration of the bacterial growth medium reduced GTF production in all strains by about 60%. Tween 80 also inhibited enzyme production and more specifically reduced GTF synthesis by the mutants. The mutations and appear to define separate genetic loci involved in regulating expression of GTF activity in


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