Background Chinese strong-flavor baijiu (CSFB) accounts for more than 70% of all Chinese liquor markets. Diverse microbes in pit mud found in the fermentation pit play a key role in CSFB production. However, the effect of spatial location on the diversity and structure of the microbial community in pit mud is still poorly understood
Results Prokaryotic microbes in different pit mud（4- and 40-year）were analyzed by using Illumina MiSeq sequencing of 16S rRNA gene. The samples were collected from pit mud that was 4 and 40 years old in the top, middle, and under parts of the cellar walls and at the bottom of them. The results showed there was no significant difference (p>0.05) in the physicochemical factors, the Observed OTU, and α-diversity between the pit mud of two different ages. The index of the 4-year-old pit mud was lower (except for total acid, which was higher than) than that of the 40-year-old pit mud. The pH, total acid, Observed OTU, Chao 1, ACE in the 4-year-old pit mud (in the top and middle part of the cellar wall) and the 40-year-old pit mud(in the top part of the cellar wall) had significant (p<0.05) difference. At the phylum level, Firmicutes (56.70%) and Bacteroidetes (26.56%) accounted for more than 80% of the overall level. For the 4-year-old pit mud sample, the dominant genuses at each location were Proteiniphilum, Lactobacillus, and Caproiciproducens, while for the 40-year-old pit mud, there were 10 common genuses accounted for more than 50% of the dominant genuses in different pit mud belong to Clostridia. The RDA analysis results showed that 85.71% of the dominant bacteria positively correlated with pH, and especially the most correlated with the total acid and available phosphorus, so its content was significantly related to the dominant bacteria (p<0.01). Therefore, it inferred that the total acid and available phosphorus were the main physicochemical factors that affected the spatial distribution of prokaryotic microbial communities in the pit mud of cellars from the liquor distillery.
Conclusions Comparing the young pit mud and the old pit mud, the structure and physicochemical factors of the prokaryotic microbial community in pit mud from Henan liquor-making company changed, and the changes occurred in the spatial location of different pits. Clostridia, which accounted for more than 50% of all types of pit mud, were responsible for the effect of total acid and available phosphorus on the microbial community. Based on the above, it provides a theoretical basis for Henan liquor-making companies in maintaining pit mud. Keywords: fermentation pit mud; spatial heterogeneity; microbial community; physicochemical factors; Chinese strong-flavor Baijiu.