Antimildew and preservation effect of Bacillus velezensis BR-1 during rice storage and its metabolic mechanism

Abstract

Stored rice susceptible to fungal contamination might cause quality deterioration and enormous grain losses. In this study, an endophytic, antagonistic strain BR-1 was isolated from rice, and its antifungal activity in vitro and in rice stored at 20 °C and 80 % relative humidity were evaluated to explore its application on quality improvement and mechanisms. Herein, the screened Bacillus velezensis BR-1 could directly degrade 54.6 % and 57.2 % zearalenone in medium and rice, respectively, with reduced cytotoxicity of degradation products. The BR-1 strain showed efficient antagonistic activity against Fusarium graminearum, its toxin production both in medium or rice, and other rice-dominant molds. Moreover, genome-wide analysis indicated that the strain encoded the key enzyme CotA laccase to degrade zearalenone, and hydrolases and lipopeptides involving in the repression of fungi growth. Subsequently, the BR-1 strain significantly (p < 0.05) reduced 52.7 % mold population and 38.4 %–55.8 % mycotoxin content in rice after 10 weeks of storage compared to the control (CK). Meanwhile, fatty acid value of treated rice decreased by 9.97 % and germination rate increased by 44.7 %. Metabolome revealed that 82 metabolites with significant difference, were identified between the treated rice and CK rice. Specifically, biosynthesis of glycerophospholipids, aspartic acid and proline significantly strengthened the defense and adaptability of rice against environmental stress. Unsaturated fatty acids as 15s-hydroxyperoxyeicosatetraenoic acid and dimorphecolic acid down-regulated, and nucleotides as guanosine and cytidine up-regulated, which was suggested the increasing endogenous antioxidant systems. This work provides an eco-friendly solution for post-harvest grain storage, with a bio-antimicrobial agent BR-1 strain for sustainable storage of rice.