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

Abstract 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.