%0 Journal Article %A Haisman, R. J. %A Jenkinson, H. F. %T Mutants of Streptococcus gordonii Challis over-producing glucosyltransferase %D 1991 %J Microbiology, %V 137 %N 3 %P 483-489 %@ 1465-2080 %R https://doi.org/10.1099/00221287-137-3-483 %I Microbiology Society, %X Two mutants of Streptococcus gordonii 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 gtf-20 and gtf-30. A double mutant (gtf-20 gtf-30) 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 gtf-20 and gtf-30 appear to define separate genetic loci involved in regulating expression of GTF activity in S. gordonii. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-137-3-483