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 ddH₂O 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.

中文翻译：

---

Bacillus velezensis MMB-51生物表面活性剂作为甘薯叶面肥高效增效剂的应用

本研究的重点是微生物生物表面活性剂作为叶面肥增效剂的应用。首次分离得到产生物表面活性剂的Bacillus velezensis MMB-51，在最佳发酵条件下，其最高产量为2.287 g/L生物表面活性剂BS-51。BS-51的化学性质被鉴定为由表面活性素和风霉素组成的脂肽，其在ddH _{2中表现出11.0 mg / L的低CMC}O 和在广泛的温度、pH 和 NaCl 浓度范围内具有良好的稳定性。然后将 BS-51 作为三种常见甘薯叶肥的增效剂施用。结果表明，BS-51使肥料与叶面的接触面积增加了51%~93%，肥料在倾斜叶面上的移动速度增加了272%~459%，表明BS-51降低了肥料的表面张力。三叶肥。BS-51还提高了从倾斜叶面滑落后的肥料残留量，根据品种不同从18.5%～21.5%增加到29.4～31.2%，从而提高了叶面肥的利用效率。此外，B. velezensis MMB-51分泌抑制甘薯病原体Ceratocystis fimbriata的生长。因此，B. velezensisMMB-51 可以作为具有抗真菌活性的作物叶面肥的高效增效剂。