Reasons of Higher Peptides Yield During Soybean Meal Solid-State Fermentation by Using Ultrasonic Pretreated Bacillus amyloliquefaciens: Spores Germination

Abstract

The aim of our investigation is to elucidate the impact of ultrasonic treated Bacillus amyloliquefaciens (B. amyloliquefaciens) on production of peptides during solid-state fermentation of soybean meal and its mechanisms. There was a substantial enhancement in levels of peptides, biomass, and protease activity within fermented soybean meal by 14.61%, 65.96%, and 16.58%, respectively, relative to control group (p < 0.05). Nevertheless, omics analysis and qRT-PCR verification declared that ultrasonic treatment did not bring the growing of B. amyloliquefaciens or the protease production in single cell, but accelerate the germination of spores. Genes encoding spo0A, spo0B, spo0F, spo0J were all substantially down-regulated ranged from − 0.25 to − 1.75 (p < 0.05). Concurrently, the gene encoding sleB displayed a remarkable up-regulation with log₂-fold change of + 3.07 (p < 0.05). Besides, their respective proteins performed the same change tendency. Moreover, after ultrasonic treatment, spores germination rate and DPA content significantly increased by 3.29 and 12.14 times, respectively. Meanwhile, OD₆₀₀ of spores suspension obviously decreased by 37.81% (p < 0.05). Most importantly, Pearson’s correlation analysis revealed that peptides yield in fermented products was strongly correlated with spores germination (Pearson’s correlation coefficient r = 0.839, p < 0.01). In brief, ultrasonic treatment promoted the germination of spores in the inoculum, which resulted in microbial proliferation and protease activity raising in fermented products, and consequently improving peptides yield. The improvement of spore germination rate after ultrasonic treatment might be achieved by reducing bacterial aggregation and lowering viscosity.