Identification of plasmids linked with polyglutamate production in Bacillus subtilis (natto).

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.