No abstract

Two novel Gram-positive bacteria, designated strains REN8T and REN14T, were isolated from baijiu pit mud in Sichuan Province, China. REN8T achieved the best growth at 37°C, a pH of 8.0, and a NaCl concentration of 2%, while REN14T displayed optimal growth at 37°C, a pH of 6.0, and a NaCl concentration of 1%. 16S rRNA and genomic phylogenetic analysis showed that REN8T and REN14T were clustered with the genus Planococcus. The genomic DNA G + C contents of REN8T and REN14T were 46.7 and 45.1 mol%, respectively. The dDDH and ANI values were 24.5 and 80.43% between REN8T and P. salinarum (the most closely related type strain) and 25.1 and 82.42% between REN14T and P. soli (the most closely related type strain). Genomic analysis showed that several carbohydrate-active enzymes and secondary metabolite gene clusters existed in REN8T and REN14T. Chemotaxonomic characteristics of REN8T and REN14T included major fatty acids, predominant menaquinones, and polar lipids, all of which were consistent with the genus Planococcus. Based on the polyphasic taxonomic method, these two strains represent two novel species of the genus Planococcus; the name Planococcus beigongshangi sp. nov. is proposed for the type strain REN8T (=JCM 33964T = GDMCC 1.2213T), and the name Planococcus beijingensis sp. nov. is proposed for the type strain REN14T (=JCM 34410T = GDMCC 1.2209T). The addition of REN8T and REN14T might improve the quality of huangjiu by considerably increasing the amino acid nitrogen content and acidity and decreasing the bioamine content, with no significant change in alcohol content.

Baijiu is a traditional distilled liquor in China. The unique flavor developed during the fermentation process of Baijiu is closely related to the microorganisms in the fermented grains of the Baijiu. Fermented grain is a solid material that has not been distilled after the fermentation of Baijiu. It is of great significance to study the bacterial diversity in fermented grains and to isolate and culture them to reveal the formation mechanism of the flavor substances in Baijiu. In this study, the diversity of bacteria in fermented grains was studied by the combination of amplicon sequencing and culturomics, and a pure culture of culturable strains was obtained. The results of amplicon sequencing showed that the bacteria detected in the fermented grains were classified into 5 phyla, 8 classes, 24 orders, 34 families, and 45 genera, of which Lactobacillus (66.95%) and Acetobacter (32.36%) were the dominant genera. By using the method of culturomics, five pH gradients (pH = 3, 4, 5, 6, and 7) of enrichment culture medium and solid medium with different components were designed to enrich and isolate the culturable bacteria in the fermented grains. A total of 323 strains of bacteria were obtained, belonging to 53 genera and 118 species, and 14 suspected new species were obtained. Among the bacteria isolated by the culturomics, 14 genera were detected by amplicon sequencing, and 39 genera were not detected, indicating that the culturomics method can isolate and culture bacteria with low abundance in fermented grains. Compared with the traditional culture method, culturomics expanded the culturable bacteria in the fermented grains to 188%. The diversity of the bacteria in the fermented grains of Baijiu was analyzed by amplicon sequencing and culturomics, and the microbial community composition and relative abundance of fermented grains were comprehensively revealed. At the same time, the acquisition of more pure cultures of culturable bacteria provides more choices for the liquor-making microbial resource library.

Traditional Chinese fermented foods are diverse and loved by people for their rich nutrition and unique flavors. In the fermentation processes of these foods, the microorganisms in the fermentation systems play a crucial role in determining the flavor and quality. Currently, some microorganisms in the fermentation systems of traditional Chinese fermented foods are in a state of being unculturable or difficult to culture, which hinders the comprehensive analysis and resource development of the microbial communities in the fermentation systems. This article provides an overview of the uncultured microorganisms in the natural environment, in the fermentation systems of traditional Chinese fermented foods, and the research methods for studying such microorganisms. It also discusses the prospects of utilizing the uncultured microorganisms in the fermentation systems of traditional Chinese fermented foods. The aim is to gain a comprehensive understanding of the microbial diversity and uncultured microorganisms in the fermentation systems of traditional Chinese fermented foods in order to better exploit and utilize these microorganisms and promote the development of traditional Chinese fermented foods.