Application of the biosurfactant produced by Bacillus velezensis MMB-51 as an efficient synergist of sweet potato foliar fertilizer

This study focused on the application of a microbial biosurfactant as a synergist of the foliar fertilizer. A biosurfactant-producing Bacillus velezensis MMB-51 was firstly isolated, which produced the peak yield of 2.287 g/L biosurfactant BS-51 at the optimum fermentation condition. The chemical nature of BS-51 was identified as lipopeptide consisting of surfactin and fengycin, which exhibited a low CMC of 11.0 mg/L in ddH(2)O and a good stability in wide ranges of temperature, pH and NaCl concentration. The BS-51 was then applied as a synergist of three common sweet potato leaf fertilizers. The result showed that BS-51 increased the contact area of fertilizer with leaf surface by 51%-93% and the moving speed of fertilizer on the inclined leaf surface by 272%-459%, indicating that BS-51 decreased the surface tension of three-leaf fertilizers. BS-51 also increased the fertilizer residue after it slipped from the inclined leaf surface from 18.5%-21.5% to 29.4-31.2% depending on their types, thereby improving the utilization efficiency of foliar fertilizer. In addition, B. velezensis MMB-51 secretion inhibited the growth of sweet potato pathogen Ceratocystis fimbriata. Therefore, B. velezensis MMB-51 could act as an efficient synergist of crop foliar fertilizer with antifungal activity.