Abstract
Fourteen of 18 strains of Bacillus subtilis (natto) were found to harbor plasmids. Twelve strains, which showed biotin requirement for growth and viscous substance productivity, contained a single plasmid species. These plasmids, including pLS15, pLS17, pLS19 and pTA1014, were classified into the same type of pUH1, the functional plasmid encoding γ-glutamyltranspeptidase (γ-GTP) gene, based on results of molecular weights and restriction patterns. Strain IFO3022, which did not require biotin but produced slightly viscous substance, harbored a single plasmid, pLS11. The plasmid pLS11 had showed a molecular weight and restriction patterns entirely different from pUH1. But the 4.2-kb BamHI fragment of pUH1 was found to be strongly hybridized with 3 fragments generated with HindIII from pLS11. Plasmid pLS11, therefore, may be a functional plasmid linked with polyglutamate (PGA) production. Strain IFO3023, which did not require biotin or produce a viscous substance, was found to have 3 plasmid species, but none of the plasmid DNA hybridized with the probe. The other 4 strains which did not require biotin or produce viscous substance did not harbor plasmid DNA. The results described above strongly suggest that the 5.7-kb plasmid, encoding the γ-GTP gene responsible for PGA production, exists widely in B. subtilis (natto) strains, which require biotin for the growth and produce PGA.
