Sporulation, competence development and biopesticide activity of a Bacillus subtilis mutant

Abstract:

Abstracts: Biocontrol Bacillus subtilis strain Bs-916 has obvious effects against Rhizoctonia solani. We demonstrated that the mutant strain, M49 obtained by means of low energy ion implantation in strain Bs-916, which produces significantly lower levels of surfactin, had no obvious effects against R. solani. [Objective] In order to identify the influencing factors of surfactin-decrease mutant strain M49, its phenotype and related gene expression levels were studied. [Methods] Strains to be tested for sporulation were grown for 24 h in sporulation medium. Plasmid pDG1728(1 μg/mL) was used for DNA transformation to test competence development of M49 and Bs-916 strains. RT-PCR (Semi-quantitative reverse transcriptase-polymerase chain-reaction) was used to determine the expression levels of selected genes involved in competence and sporulation in both the wildtype Bs-916 and mutant M49 strains, such as comS, rapA, rapC gene. [Results] Our data showed that mutant strain M49 confers a leaky competence phenotype, typified by a ten-fold reduction. This indicated a fact that DNA fragments are more easily transformed to wildtype strain than M49 mutant. The M49 strain also appeared to exhibit a sporulation-deficient phenotype, compared with the wild-type Bs-916, its spore’s number declined by about 75%. RT-PCR results showed that both the comS and rapC genes were expressed in the Bs-916 strain but not in the M49 strain. [Conclusions] These results indicate that surfactin production, spore formation and competence development of Bacillus subtilis mutant strain M49 are severely decreased. And then, our data implicated that the cause of spore formation and antifungal activity may be the mutation of three key amino acids in ComA protein.