Daqu is a traditional starter for Baijiu fermentation and is produced by spontaneous fermentation of ground and moistened barley or wheat. The quality of Daqu is traditionally evaluated based on physicochemical and subjective sensory parameters without microbiological analysis. Here, we compared the physicochemical characteristics of qualified (QD) and inferior (ID) Daqu, their microbial communities based on plate counting and PacBio SMRT sequencing of rRNA gene libraries, and their impacts on Baijiu fermentation. The results showed that the glucoamylase and α-amylase activities of QD were significantly higher than those of ID. The counts of yeasts and relative abundances of functional microbes, especially the amylolytic bacterium Bacillus licheniformis and fungi Saccharomycopsis fibuligera and Lichtheimia ramosa, were significantly higher in QD than in ID. The laboratory-scale Baijiu fermentation tests showed that the relative abundances of the amylolytic microbes were higher in the QD than the ID fermentation set, resulting in more efficient fermentation, as indicated by more weight loss and higher moisture content in the former. Consequently, more glycerol, acetic acid, ethanol, and other volatile compounds were produced in the QD than in the ID fermentation set. The results suggest that Daqu quality is determined by, and can be evaluated based on, its microbial community.

Medium-temperature Daqu (MT-Daqu) serves as a crucial saccharifying and fermentation agent in the production of strong-flavor Baijiu. Due to the spatial heterogeneity of solid fermentation, significant differences occurred in the fermentation state and appearance features in different parts of Daqu during fermentation. Currently, the understanding of the underlying mechanism behind this phenomenon remains limited. Here, we analyzed the microbial succession and assembly models and driving factors in different parts of MT-Daqu at the species level based on the PacBio single-molecule real-time sequencing technology. The results showed significantly different bacterial and fungal community compositions, successions, and interaction patterns in different parts of MT-Daqu. The bacterial community composition and succession model in the middle layer were similar to those in the core layer, whereas the fungal community composition and succession model in the surface layer were similar to those in the middle layer. The co-occurrence network analysis showed that microbial interaction is stronger in the middle and core layers than in the surface layer. Analyses based on both niche theory and neutral theory models indicated that deterministic processes predominantly governed the microbial community assembly and these processes played an increasingly important role from the surface to the core layer. Random forest analysis revealed that temperature was the primary endogenous factor driving the bacterial and fungal community assembly. The results of this study contribute to a better understanding of the microbial community in MT-Daqu and are helpful for the quality control of MT-Daqu fermentation.

Medium-temperature Daqu (MTD) serves as the saccharification and fermentation starter for Nongxiangxing Baijiu. Flipping Daqu (FD) during fermentation is a key craft in traditional MTD preparation. However, the mechanism underlying this flipping craft remains unclear. To address this, we systematically compared FD with non-flipping Daqu (NFD) to elucidate microbial succession dynamics, metabolic phenotypes, and environmental drivers. Our results demonstrated divergent microbial community succession patterns between FD and NFD during the stable fermentation phase (days 9-25). FD exhibited significantly higher enzyme activities and volatile ketone content, along with lower core temperatures compared to NFD. Metabolite production in FD was influenced by both bacteria and fungi, whereas fungi predominantly controlled metabolite production in NFD. Co-occurrence network analysis revealed that the microbial community in FD was simpler yet more stable compared to that in NFD. Microbial succession in MTD was primarily driven by interspecies interactions and environmental factors. Furthermore, deterministic processes and stochastic processes jointly governed microbial assembly both FD and NFD, with temperature, moisture, and acidity as the key driving factors. These findings highlight the pivotal role of the flipping crafts in enhancing microbial functionality and metabolic diversity, offering a theoretical basis for optimizing MTD production and advancing intelligent fermentation systems.

Fermented foods have been produced by humans since prehistoric times and are consumed worldwide today due to their enhanced nutritional value, taste and flavor, and benefits for human health. Various microorganisms are essential agents responsible for food fermentation and have been extensively studied using both culture-dependent and -independent methods. However, previous research has mainly focused on fermented foods produced on a large scale in urbanized areas. In this study, we collected 255 samples of diverse traditional fermented foods—including alcoholic beverages, amylolytic starters, fruit vinegar, and fermented products of milk, vegetables, cereals, legumes, fish, meat, and other materials—from ethnic minority areas of China through a citizen science initiative for the study of yeast diversity. A total of 516 yeast strains were isolated, and 81 yeast species, including four new species, were identified based on sequence analyses of the D1/D2 domain of the large subunit rRNA gene and the internal transcribed spacer region. The proposals of the new species were further supported by whole-genome average nucleotide identity (ANI) analysis. The dominant species isolated were Saccharomyces cerevisiae, Pichia kudriavzevii, Wickerhamomyces anomalus, Saccharomycopsis fibuligera, and Clavispora lusitaniae. The new species are described as Blastobotrys guizhouensissp. nov., Wickerhamiella shiruiisp. nov., Trichosporon jiuqusp. nov., and Parajaminaea albasp. nov. This study demonstrates the high yeast diversity in traditional fermented foods of ethnic minorities in China. These yeast resources are of special value for both basic and applied research in the future.

In the survey of yeast diversity in high-temperature Daqu, which is a fermentation starter for Chinese sauce-flavoured Baijiu, six yeast strains representing one novel species of the genus Starmerella were isolated from samples of Daqu and surrounding environments collected in Zunyi city, Guizhou Province, China. Phylogenetic analyses of the internal transcribed spacer (ITS) region and the D1/D2 domains of the large subunit rRNA gene indicate that these six strains are conspecific with three other strains isolated from flowers and duckweed collected in Samoa, India and Thailand. The representative strain QFC-8 of the new species differs from the closet species Starmerella caucasica resolved by the D1/D2 sequence analysis by 13 (3.1 %, 12 substitutions and 1 gap) and 40 (10.3 %, 9 substitutions and 31 gaps) mismatches in the D1/D2 domain and ITS region, respectively. The results suggest that the novel group represents an undescribed species in the genus Starmerella, for which the name Starmerella fangiana sp. nov. is proposed. The holotype strain is CGMCC 2.7773.

An orange-coloured yeast strain was recently isolated from rotted leaves in Zunyi City, Guizhou Province, PR China. Phylogenetic analysis revealed that this strain shares identical or similar sequences with no more than two to three nucleotide substitutions in both the 26S rDNA D1/D2 domains and the internal transcribed spacer (ITS) region with three other strains isolated from decayed wood in Indonesia, mushroom in Thailand and a plant of the genus Opuntia in the Bahamas. Therefore, these strains are conspecific. And they are most closely related to Rhodotorula paludigena but exhibit sequence divergences of 2.1–2.6% in the 26S rDNA D1/D2 domains and 2.9–3.2% in the ITS region. Physiologically, strain CGMCC 2.7770 differs from R. paludigena in its ability to assimilate maltose, l-arabinose and citric acid. Both the phylogenetic analysis and phenotypic characteristics indicate that those four strains represent a novel species in the genus Rhodotorula, for which the name Rhodotorula silvicola sp. nov. is proposed (holotype CGMCC 2.7770^T).