Bacterial composition in pit mud of Yanghe liquor and identification of acid producing bacteria

Abstract:

[Background] Microbial composition of pit mud and metabolites of the endogeneous bacteria are a few of the main factors that affect the synthesis of butyrate and caproic acid during Luzhou-flavor liquor fermentation. [Objective] To reveal the bacterial community of pit mud of Luzhou-flavor liquor at different ages and discover organic acid production capacity of anaerobes, and to clarify the correlation between them. [Methods] The composition of bacteria in pit mud was analyzed by sequencing the 16S rRNA gene using Illumina HiSeq high-throughput platform. Anaerobes in the pit mud were isolated by selective culturing and their metabolic properties were analyzed by comparing the ability of producing butyrate and caproic acid. [Results] Bacteria in the pit mud of Yanghe liquor were mainly distributed in Clostridia, Bacteroidia, Synergistia and Bacilli. The abundance of Hydrogenispora and Ruminiclostridium in 20 years pit mud increased significantly compared with that in 3 or 5 years pit mud. Correlation analysis showed that Ruminiclostridium was the most influential core microorganism. The mutual promotion relationship between bacteria associated with Clostridium was also predicted. Twenty anaerobes belonging to Clostridiales were isolated from the pit mud by traditional culturable methods. Strains of genus Clostridium produced more acids than others, Clostridium tyrobutyricum showed the most significant butyrate production capacity, while Clostridium butyricum had the strongest caproic acid production capacity. Strains with highest capability of producing butyrate were isolated from 5 and 20 years pit mud, and strains with highest capability in producing caproic acid were isolated from 20 years pit mud. [Conclusion] Understanding the composition and role of bacteria in pit mud aged for different years could help better control of the synthesis of volatiles of Chinese liquor.