Characterisation of Streptomycin resistant mutants of biocontrol Bacillus strains

Abstract

A good antibiotic-producing Bacillus subtilis and an elevated extracellular enzyme-secreting Bacillus amyloliquefaciens biocontrol strain were investigated. The B. subtilis strain produces non-ribosomal oligopeptides: iturin, surfactin and fengycin. These cyclic lipopeptides have antifungal and antibacterial effects. The B. amyloliquefaciens strain secrets many extracellular enzymes (proteases, chitinases, cellulases and lipases); these have great significance in the antagonism. Kurosawa and co-workers reported elevated protease and P-amylase secretion from streptomycin-resistant B. subtilis mutants. We isolated twenty spontaneous streptomycin resistant mutants from our B. subtilis strain and four spontaneous streptomycin resistant mutants from the B. amyloliquefaciens strain. We investigated the extracellular enzyme and antibiotic production of the mutants. Some of the mutants showed elevated enzyme and antibiotic secretion. The rpsL gene in theses spontaneous streptomycin resistant mutants, were sequenced and point mutations were detected in it, so very likely the changes of the structure of the rpsL protein is responsible in some cases for the elevated enzyme and depsipeptide production.