Isolation of the Antimicrobial Cyclic Peptide Subtilosin a from a Gut-Associated Bacillus subtilis Strain

The endospore-forming Bacillus subtilis has been used as probiotics over the last 50 years. However, little is known on how Bacillus spp act in the gut compared to other well-characterized probiotics such as lactic acid bacteria. It is believed that the competitive exclusion of pathogens results from different mode of action notably the production of antimicrobial compounds such as bacteriocins. Here, we report the characterization of the unexpected ability of a gut-associated B. subtilis BSP1 to synthetize the cyclic bacteriocin subtilosin A at high level. Our findings suggest that the BSP1 phenotype could be related, at least in part, to a subsequent increased expression level of the subtilosin A biosynthetic gene cluster sbo-alb in response to a higher activity of the stationery and sporulation master regulator Spo0A.