Molecular interpretation of flavor improvement for Pixian Douban fermented with Bacillus bioaugmentation in the tank based on whole-genome and metatranscriptomics.

Abstract

Considering the flavor disadvantages of the strong acidity and whole pungency in Pixian Douban (PXDB) of the tank fermentation, an improvement was obtained by the bioaugmentation of B. licheniformis JY and B. atrophaeus XY, and the underlying mechanism was explored by whole-genome and metatranscriptomics. The key volatiles contents especially for phenethyl alcohol, 1-nonanal, and 4-ethylphenol were increased by Bacillus bioaugmentation while the acid content was reduced. The metatranscriptome analysis indicated that Zygosaccharomyces and Bacillus were the dominant strains in the group of Bacillus bioaugmentation while the key life functions of microorganisms remained highly active, effectively driving the metabolic activities related to flavors. The multi-omics analysis showed that the metabolic activities related to the flavors of the initial fermentation were promoted by the up-regulated DEGs while the metabolic activities like protein synthesis in the later fermentation was inhibited by the down-regulated DEGs. Seven DEGs of significant expression in the predicated metabolic pathways of these two Bacillus strains were found, which implied a promotion of the downstream pathways that could contribute to the flavor improvement, providing a potential explanation for the flavor improvement of the product. The combined analysis of the sample qualities and multi-omics results indicated that the Bacillus bioaugmentation was effective but declined with fermentation time, suggesting a necessary of keeping bioaugmentation by regularly adding Bacillus strains. The results of this study provided a potential interpretation for Bacillus bioaugmentation in the PXDB fermentation, which offered a reference for the microbial agent development of PXDB fermentation in the tank.