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The pit is the necessary bioreactor for brewing process of Chinese strong-flavor liquor. Pit mud in pits contains a large number of microorganisms and is a complex ecosystem. The analysis of bacterial flora in pit mud is of great significance to understand liquor fermentation mechanisms. To overcome taxonomic limitations of short reads in 16S rRNA variable region sequencing, we used high-throughput DNA sequencing of near full-length 16S rRNA gene to analyze microbial compositions of different types of pit mud that produce different qualities of strong-flavor liquor. The results showed that the main species in pit mud were Pseudomonas extremaustralis 14-3, Pseudomonas veronii, Serratia marcescens WW4, and Clostridium leptum in Ruminiclostridium. The microbial diversity of pit mud with different quality was significantly different. From poor to good quality of pit mud (thus the quality of liquor), the relative abundances of Ruminiclostridium and Syntrophomonas in Firmicutes was increased, and the relative abundance of Olsenella in Actinobacteria also increased, but the relative abundances of Pseudomonas and Serratia in Proteobacteria were decreased. The surprising findings of this study include that the diversity of intermediate level quality of N pit mud was the lowest, and the diversity levels of high quality pit mud G and poor quality pit mud B were similar. Correlation analysis showed that there were high positive correlations (r > 0.8) among different microbial groups in the flora. Based on the analysis of the microbial structures of pit mud in different quality, the good quality pit mud has a higher microbial diversity, but how this higher diversity and differential microbial compositions contribute to better quality of liquor fermentation remains obscure.

Abstract. Strong-aroma type liquor occupies over 70% of Chinese liquor market, but the namelist of key microbes responsible for liquor flavor is still vague. Lots of data indicate that the interface between the bottom pit mud and Zaopei (fermented grains) plays an important role for aroma molecule production, so isolation and characterization of anaerobic microbial species from the interface is of great importance. In this study, a specific culturing medium was prepared with the bottom pit mud and Zaopei materials to isolate over a hundred colonies, some of which were characterized mainly as Clostridia and Lactobacillus microbes using the full-length 16S rDNA sequencing; but not all of them can be classified into species at high confidence levels, suggestive of novel anaerobic species.

Abstract. In this study the microbial composition in the starter (Daqu) of Chinese Gujing Tribute liquor was determined by employing near full length ribosome gene library sequencing approach. Gujing Tribute Daqu has a distinct microbial community structure by comparison with several other important types of Chinese liquor; especially The rmomyces only occurred in Gujing Tribute Daqu, not in any other types of Daqu as most dominant species. Besides, there are five distinct species as most dominant ones in Gujing Tribute Daqu: Pantoea agglomerans, Pantoea vagans, Talaromyces thermophiles, Thermomyces lanuginosus, and Thermoascus aurantiacus, the latter two species both capable of producing a series of useful enzymes for fermentation purposes and some flavor precursor synthesis. Though the distinct dominating species are mainly the ones degrading the feedstock, their potential roles in the flavor determination of Gujing Tribute liquor are very valuable for further study.