Characterization and Safety Evaluation of Surfactin from Bacillus methylotrophicus Effective against Streptomyces scabies, the Causative Agent of Potato Common Scab

Potato common scab is a soil-borne disease caused by Streptomyces scabies that affects potato farming, but there is no safe and efficient control method so far. The aim of this study was to isolate and purify the antimicrobial compound from the Bacillus methylotrophicus SJ80 and SJ-81 to prevent potato common scab (S. scabies). S. scabies was used as an indicator bacteria to track the antibacterial activity. Compounds SJ-1 from B. methylotrophicus SJ80 and SJ-2 from B. methylotrophicus SJ81 antagonized S. scabies were isolated and purified. The structure of compounds was determined by MALDI-TOF-MS and NMR, and found that both of them were cyclic lipopeptides with molecular formula of C53H93N7O13, the structure of SJ-1 had been reported while SJ-2 was rare due to the difference of heptapeptide. Furthermore, it was proved that the SJ-1 and SJ-2 were biologically safe through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cytotoxicity as well as life activity assessment for Caenorhabditis elegans. Our study demonstrated that lipopeptides SJ-1 and SJ-2 from the cultures of B. methylotrophicus SJ80 and SJ81 have the potential to be developed as biological control agents.