Poly-gamma-glutamic acid improves the drought resistance of maize seedlings by adjusting the soil moisture and microbial community structure

Drought is an important factor affecting crop yield, and consequently, much research attention is being paid to enhancing the drought tolerance of plants for improving crop production. A new type of biological super-absorbent polymer, poly-gamma-glutamic acid (gamma-PGA), has important water-saving applications in agriculture. In this study, two Bacillus subtilis strains, P1 and Y2, were used to produce gamma-PGA, and the effects of gamma-PGA fermentation broth on maize seedling growth, soil physico-chemical properties, and microbial community structure were analyzed. The results showed that gamma-PGA fermentation broth significantly increased maize seedling biomass, soil water content, and bacterial and fungal biomass. Bacteria such as Lysobacter, Spingomonas and Haliangium of Proteobacteria; Actinomadura and Lamia of Actinobacteria; and unidentified Acidobacteria of Acidobacteria as well as fungi such as Talaromyces and Fusarium of Ascomycota and Rhizopus of Zygomycota were dominant in the rhizosphere soil of maize. Compared to the watering treatment, the gamma-PGA fermentation broth treatment remarkably increased the relative abundance of plant growth-promoting bacteria such as Bacillus, Pseudomonas, and Burkholderia. In summary, the gamma-PGA fermentation broth produced by B. subtilis P1 and Y2 could improve the drought resistance of maize seedlings by adjusting the soil moisture and microbial community structure.