Bacillus licheniformis affects the microbial community and metabolic profile in the spontaneous fermentation of Daqu starter for Chinese liquor making

Bioactive compounds from food-grade Bacillus

Bacillus species have attracted significant attention in recent years due to their potential for producing various bioactive compounds with diverse functional properties. This review highlights bioactive substances from food-grade Bacillus strains and their applications in functional foods and nutraceuticals. The metabolic capacities of Bacillus species have allowed them to generate a wide range of bioactive substances, including vitamins, enzymes, anti-microbial peptides, and other non-ribosomal peptides. These substances have a variety of positive effects, including potential cholesterol-lowering and immune-modulatory qualities in addition to anti-oxidant and anti-bacterial actions. The uses and mechanisms of action of these bioactive chemicals can be used to improve the functional qualities and nutritional profile of food products. Examples include the use of anti-microbial peptides to increase safety and shelf life, as well as the use of Bacillus-derived enzymes in food processing to improve digestibility and sensory qualities. The exploitation of bioactive compounds from food-grade Bacillus strains presents a promising frontier in the development of functional foods and nutraceuticals with enhanced health benefits. Due to their wide range of activity and applications, they are considered as important resources for the development of novel medications, agricultural biocontrol agents, and industrial enzymes. Ongoing research into the biosynthetic pathways, functional properties, and applications of these compounds is essential to fully realize their potential in the food industry. This review underscores the significance of various bioactive compounds generated from Bacillus in tackling global issues like environmental sustainability, sustainable agriculture, and antibiotic resistance. Future developments in microbiology and biotechnology will enable us to fully utilize the potential of these amazing microbes, resulting in novel approaches to industry, agriculture, and health. © 2024 Society of Chemical Industry.

Metagenomic and Physicochemical Analyses Reveal Microbial Community and Functional Differences Between Three Different Grades of Hongxin Low-Temperature Daqu

Hongxin (HX) is an indispensable Daqu in the production of light-flavor Baijiu (LFB). However, the classification method of HX is highly subjective, and the classification and functional differences in microorganisms in different grades of HX are still unclear. In this study, metagenomics and physiochemical analysis were used to compare three grades of HX (top, first, second) and clarify their brewing functions in LFB. The results showed that a total of 1556 genera and 5367 species were detected in all samples. Bacteria and fungi are the main microorganisms in HX, and the relative abundance of bacteria and fungi is above 4.5:1. Kroppenstedtia (11.43%), Leuconostoc (10.52%), Fructilactobacillus (9.00%) were the top three genera in HX. Although the microbial community composition of the three grades of HX is highly similar, each HX has a specific microbial community structure and macrogene functional characteristics, indicating that they have different brewing functions. The dominant microorganisms in top-grade HX and first-grade HX were mainly positively correlated with energy metabolism and lipid metabolism, while the dominant microorganisms in second-grade HX were mainly positively correlated with carbohydrate metabolism and amino acid metabolism. This study revealed the different fermentation effects of different grades of HX in LFB and provided suggestions for the scientific classification and quality control of HX.

Screening and identification of strains for high quality and antioxidant activity of Baijiu from strong-flavor Daqu and analysis of microbial synergistic effects

In this study, functional strains with strong fermentation characteristics were isolated from Strong-flavor Daqu and evaluated for their ability to enhance the quality and antioxidant activity of Baijiu. Bacillus velezensis (S1), Bacillus subtilis (S12), and Escherichia coli (S16) were identified as key strains. Fermentation experiments with different inoculation amounts and combinations revealed synergistic effects on Baijiu quality and antioxidant activity. Specifically, the total ester content in Baijiu fermented with 3% of S1, S12 and S16 were increased by 5.68%, 53.41% and 70.45% respectively, while the DPPH radical scavenging rate was increased by 52.01%, 17.63% and 35.52%, respectively, compared with the Baijiu fermented only with Daqu. Multi-strain combinations, particularly 4%-S16+2.5%-S1 and 3%-S16+4%-S12, exhibited notable antioxidant activity and ester content. Furthermore, the inoculation of 3% E. coli, 2% B. velezensis and 4% B. subtilis combination significantly increased total ester content (1.94 g/L) and antioxidant activity (38.09%) of Baijiu, in which S1 increased antioxidant activity of Baijiu while S12 increased total ester content. The results of GC-MS indicated that biofortified fermentation produced high levels of esters and guaiacol and its analogues, facilitated by synergistic interactions among indigenous microorganisms. This study is helpful to provide a new perspective and insight for improving Baijiu flavor and antioxidant activity.

Temporal and Workshop Heterogeneity of Microbial Communities with Physicochemical Properties and Flavor Substances During Stacked Fermentation of Sauce-Flavor Baijiu

Even within the same round of stacked fermentation, variations among production workshops can significantly influence microbial communities and physicochemical parameters. In this study, stacked fermented grains from the fourth round of sauce-flavor Baijiu production were utilized to explore the impact of spatial variations on fermentation. High-throughput sequencing technology was employed to comprehensively analyze the microbial community composition and its dynamic changes during the fourth cycle of stacked fermentation in sauce-flavor Baijiu across different workshops. Our results revealed that the predominant genera in both workshops included Saccharomycetales, Thermomyces, Monascus, Ascomycota, Kroppenstedtia, Bacillus, and Virgibacillus. Differences in physicochemical factors during the fermentation process led to distinct microbial successions among workshops. Key drivers of dominant microbial community succession, such as glucose, starch, ethanol, and temperature, were identified during the fourth round of stacked fermentation. Differences in the types and contents of significant flavor substances in different workshops are related to the complex role of the microbial community. Acetic acid is the most different flavor substance in both workshops, and the content of acetic acid affects the synthesis of ethyl ester substances, which has significant correlation with the regulation of fungal communities, especially Saccharomycetales. These findings provide valuable insights into the brewing mechanisms of the stacked fermentation process and offer guidance for formulating more refined control strategies to optimize the liquor-making process.

Application of indigenous Saccharomycopsis fibuligera for light-flavor Baijiu fermentation: Changes of microbial community and flavor metabolism

Ethyl acetate, a characteristic flavor compound in light-flavor Baijiu (LFB), plays a pivotal role in defining its sensory profile. Insufficient concentrations in fermented grains may diminish the quality of Baijiu. Indigenous microbial bioaugmentation has proven effective in improving Baijiu quality by reshaping microbial community and modulating flavor metabolism within fermentation ecosystems. This study investigated the effects of Jiuqu fortified with an indigenous Saccharomycopsis fibuligera Y162 on the microbial community, physicochemical parameters, and volatile compound profiles throughout the fermentation of LFB. Results demonstrated a significant increase in ethyl acetate content in both original Baijiu and fermented grains, alongside pronounced fungal community restructuring. PacBio single-molecule real-time (SMRT) sequencing analysis showed that Lactobacillus helveticus, Rhizopus sp., Saccharomyces cerevisiae, and Issatchenkia orientalis became the dominant species at the end of fermentation. Correlation network analysis revealed that ethyl acetate was significantly related (P < 0.05, |ρ| > 0.7) to the I. orientalis and Rhizopus sp. (the main fungal biomarkers), which was driven by the functional S. fibuligera. Mantel test further highlighted acidity, temperature, and moisture as critical environmental factors influencing the microbial community (P < 0.05, |ρ| > 0.7). To summarize, biofortification with S. fibuligera exhibited positive effects in enhancing typical flavor metabolites by influencing fungal community structure in LFB. These findings imply that the indigenous strains have great application potential in improving the quality of Baijiu.

Deciphering the fungal symphony: unveiling the fungal dynamics during the fermentation of traditional Chinese strong-flavor Daqu

Daqu, a starter culture rich in microorganisms like bacteria and fungi, is central to vinification and liquor brewing, yet fungal contributions are often understudied. In this study, we used Illumina MiSeq sequencing to investigate the succession of fungal community during Chinese strong-flavor liquor fermentation. The results showed that the alpha and beta diversity of fungal community were significantly different during Daqu fermentation. The dominant phyla and genera are Ascomycota and Saccharomycopsis, respectively. Co-occurrence network analysis identified 10 keystone species during Daqu fermentation, displaying that the positive correlations (99.64%) dominated the fungal network. The redundancy analysis showed that moisture has the most significant influence on the Daqu fungal community. Concurrently, a robust association was observed between 10 keystone fungal genera and environmental parameters such as acidity and moisture. These findings not only elucidated the intricate dynamics of the fungal community succession and the interplays among fungi but also pinpointed the primary drivers of the fungal community and its keystone species during the Daqu fermentation process. Ultimately, this research presented novel perspectives for enhancing the quality and precision of liquor production by shedding light on the central role of keystone species in maintaining community stability and their adaptive responses to environmental stimuli.

Characterization and Correlation Analysis of Bacterial Composition and Physicochemical Quality in High- and Medium-Temperature Daqu from China's Binzhou Region

To investigate the bacterial community structure and physicochemical characteristics of different types of Daqu in the Binzhou region, this study employed traditional pure culture methods, high-throughput sequencing technology, and conventional physicochemical assays for analysis. The research results indicate that Enterococcus faecium and Bacillus licheniformis emerged as the main LAB and Bacillus species in Daqu from Binzhou region, respectively. In addition, high-throughput sequencing revealed significant differences in bacterial community structure between the two types of Daqu (P < 0.01). Compostibacillus and Sebaldella were identified as the biomarkers and potential key strains of high- and medium-temperature Daqu, respectively, and high-temperature Daqu demonstrated higher microbial complexity and stability than medium-temperature Daqu. Physicochemical assays demonstrated that the a* value, Daqu skin hardness, Daqu core hardness, density, starch content, and aminophenol content being significantly higher in high-temperature Daqu (P < 0.05), meanwhile, the L* value, water activity, water content, protein content, liquefaction power, and saccharification power were found to be significantly lower in high-temperature Daqu (P < 0.05). And there was significant association between dominant genera and the physicochemical indexes of Daqu (P = 0.001). It can thus be seen that there were significant differences between the microbial communities and physicochemical indicators of different types of Daqu in the Binzhou region. The results of this study are of great significance for further analyzing the differences between different types of Daqu and improving their quality.

Functional microbiome assembly in food environments: addressing sustainable development challenges

The global food system faces numerous challenges, creating an urgent need for sustainable reform. Functional microbiome assemblies offer transformative potential by endowing microbial foods with diverse, beneficial characteristics. These assemblies can dynamically influence specific food systems, positioning them as a promising approach for reshaping food production. However, the current applications and types of microbiome assemblies in foods remain limited, with a lack of effective screening and regulatory methods. This review introduces the functions and practical approaches for implementing microbiome assemblies in food systems alongside future directions for enhancing their applications. Several ecological studies evaluated how to regulate functional output and revealed that environmental conditions, which shape the niche for species survival, significantly influenced the functional output of microbiomes. Building on this theoretical foundation, this review presents a model for functional output comprising niche conditions, functional gene codes, and corresponding functional outputs. This model is illustrated with examples to explore sustainable applications and regulatory mechanisms for functional microbiome assemblies. By highlighting the roles of functional outputs in food systems and examining the potential for food environments to induce and modulate microbiome functions, this review provides a roadmap to address emerging challenges in food sustainability.

Precipitation and temperature drive microbial community changes affecting flavor quality of Nongxiangxing Daqu

Nongxiangxing Baijiu is the most famous Baijiu flavor in China, and its characteristic style is closely related to Nongxiangxing Daqu used in fermentation. However, there are few reports about the difference of Daqu quality between seasonal variations. In this study, precipitation and temperature drove changes in microbial communities that resulted in differences in the flavor of Daqu produced in different seasons. For example, the average daily temperature in summer was as high as 27.29 ± 2.24 °C, which was significantly higher than other seasons (p < 0.01). Bacillus was abundant in the Daqu produced in this season, while tetramethylpyrazine flavor was more prominent, up to 1556.95 ± 153.92 μg/kg. Metabolomics studies identified major pathways associated with the weak flavor of spring_Daqu. In addition, LEFSe analysis revealed the marked microorganisms in different seasons. These results revealed the differences in seasonal Daqu, thus contributing to the scientific and rational use of Daqu.

Differences in microbial communities among different types of zaopei and their effects on quality and flavor of baijiu

Three types of zaopei (fermented grain) of xiaoqu light-flavor baijiu (XQZP), daqu light-flavor baijiu (DQZP), and strong-flavor baijiu (SFZP) at the end of fermentation and their dominant lactic acid bacteria were systematically compared and analyzed in this study. The results showed that these three types of zaopei differed significantly in acidity, reducing sugar content, and ethanol content, and that the main factors influencing their microbial community were acidity and lactic acid. The diversity and contents of flavor substances were significantly higher in SFZP than in DQZP and XQZP. Additionally, there was a strong correlation between dominant lactic acid bacteria and flavor substances in all three zaopei, but the correlation between fungi and flavor substances was higher than that between bacteria and flavor substances. Differential gene analysis revealed that the microbial activities followed the order of SFZP > DQZP > XQZP. The KEGG enrichment analysis indicated that the differential genes from different zaopei were enriched in different metabolic pathways. Furthermore, various microorganisms in 3 types of zaopei contained different functional genes, of which fungi mainly contained genes responsible for the synthesis of ethanol and acetic acid, while lactic acid bacteria mainly contained genes responsible for the synthesis of lactic acid. In XQZP, L. helveticus was dominant lactic acid bacteria prominent in acetic acid tolerance and lactic acid production; in DQZP, L. acetotolerans was remarkable in its tolerance to lactic acid, acetic acid, ethanol and lactic acid production; and in SFZP, A. jinshanensis was superior in acetic acid tolerance and production. Taken together, this study reveals the mechanism underlying flavor differences among three types of baijiu and provides valuable references for the development and utilization of baijiu microbial resources.

Effect of Mixed Strains on Microbial Community and Flavor Metabolites in Fermentation Process of Chi-Flavor Baijiu

The distinct flavor of chi-flavor baijiu (CFB) has garnered significant attention in China. After the optimization of fermentation conditions, Pichia anomala and Lactobacillus plantarum were introduced into the fermentation process to enhance the flavor. Samples inoculated with these mixed strains (SY) exhibited higher levels of alcohol (from 33.04 to 178.55 mg/L) and esters (from 49.51 to 130.20 mg/L) compared to the control group (KB). In SY, P. anomala and L. plantarum were the predominant microorganisms, while Pediococcus and Saccharomyces were more prevalent in KB. Moreover, 68 volatile flavor compounds were detected in SY, as opposed to 64 in KB. Notably, Pichia showed a positive correlation with key flavor compounds. The synergistic fermentation with exogenous strains led to a 52.38% increase in phenethyl alcohol and a 4.91% increase in ethyl lactate. Additionally, the levels of other flavor compounds, like ethyl acetate, γ-nonanolactone, and (E)-2-octenal, also increased. The results demonstrated that the addition of P. anomala and L. plantarum to the fermentation process of CFB significantly increased the contents of flavor compounds. This research reveals valuable insights into flavor enhancement and the microbial community dynamics in CFB production.

Unraveling the regional environmental ecology dominated baijiu fermentation microbial community succession and associated unique flavor

Chinese baijiu as one of the famous distilled liquor in which fermented in open environments, with various microorganisms (i.e., bacteria, fungi, and yeast) involved in their brewing process, and created corresponding unique flavor. However, the sources of environmentally enriched microbial communities associated with liquor fermentation are still being characterized yet. Given the dependence of microbial growth and reproduction on environmental ecology, it is important to understand the correlation between baijiu fermentation microbial community and surrounding environmental ecology (i.e., temperature, humidity, wind, and precipitation). This study systematically overviewed the sources of microorganisms in the Jiang-flavor-Baijiu fermentation system. The results showed that microorganisms in baijiu brewing (i.e., mold, lactic acid bacteria, and yeast) mainly originated from surrounding environmental matrices, including the air (i.e., Yeast, Streptomyces and Bacillus), soil (i.e., Xanthomonas, Methanococcus and Comamonas) and water (i.e., Flavobacterium, Acinetobacter, and Pseudomonas) via atmospheric transport, raw material transfer and surface runoff. In addition, the unique baijiu fermentation microbial community diversity depends on local geology and meteorological conditions, highlighting that the structural stability and diversity of the microorganisms in the Baijiu brewing process dominated by local environmental ecology. We also explored the regional environmental conditions on the microbial community and found that the unique Jiang-flavor-Baijiu fermentation microbial community diversity depends on local geology and meteorological conditions. The Jiang-flavor-Baijiu workshop is located in the basin of the middle-and low latitude mountainous areas, with sufficient solar irradiation and rainfall, high air humidity, and low wind speed that favor the growth and propagation of Baijiu fermentation microorganisms. Therefore, the obtained conclusions provide new insights unraveling the key factor controlling the unique flavor of Chinese Baijiu, where protecting the ecology of baijiu brewing-regions is fundamental for maintaining the long-term quality of baijiu.

Dynamic Changes and Potential Correlations between Microbial Diversity and Volatile Flavor Compounds in Chinese Medium-Temperature Daqu during Manufacturing

To investigate the dynamic changes and potential correlations between microbial diversity and volatile organic compounds (VOCs) during Chinese medium-temperature Daqu (MTD) manufacturing at different key stages, in this study, high-throughput sequencing (HTS) and gas chromatography-ion mobility spectrometry (GC-IMS) were employed to analyze the microbial diversity and VOCs of MTD, respectively. The results showed that Weissella, Staphylococcus, Thermoactinomyces, Kroppenstedtia, and Lactobacillus were the dominant bacterial genera, while Aspergillus, Alternaria, Thermoascus, Thermomyces, Wickerhamomyces, and Saccharomyces were the dominant fungal genera. A total of 61 VOCs were detected by GC-IMS, among which, 13 differential VOCs (VIP > 1) were identified, that could be used as potential biomarkers to judge the fermentation stage of MTD. Kroppenstedtia and Saccharopolyspora were positively correlated with 3-methyl-2-butenal and 2,2,4,6,6-pentamethylheptane-D, respectively, and both of these were positively correlated with butanal-D. Acetobacter, Streptomyces, and lactic acid bacteria (LAB) including Leuconostoc, Pediococcus, Weissella, and Lactobacillus were negatively correlated with their associated VOCs, while fungi were generally positively correlated with VOCs. Wickerhamomyces, Saccharomyces, and Candida were positively correlated with butan-2-one-M. This study provides a theoretical basis for explaining the mechanisms of MTD flavor formation and screening functional microorganisms to improve the quality of MTD.

Species-level understanding of the bacterial community in Daqu based on full-length 16S rRNA gene sequences

Daqu is used as the fermentation starter of Baijiu and contributes diversified functional microbes for saccharifying grains and converting sugars into ethanol and aroma components in Baijiu products. Daqu is mainly classified into three types, namely low (LTD), medium (MTD) and high (HTD) temperature Daqu, according to the highest temperatures reached in their fermentation processes. In this study, we used the PacBio small-molecule real-time (SMRT) sequencing technology to determine the full-length 16 S rRNA gene sequences from the metagenomes of 296 samples of different types of Daqu collected from ten provinces in China, and revealed the bacterial diversity at the species level in the Daqu samples. We totally identified 310 bacteria species, including 78 highly abundant species (with a relative abundance >0.1% each) which accounted for 91.90% of the reads from all the Daqu samples. We also recognized the differentially enriched bacterial species in different types of Daqu, and in the Daqu samples with the same type but from different provinces. Specifically, Lactobacillales, Enterobacterales and Bacillaceae were significantly enriched in the LTD, MTD and HTD groups, respectively. The potential co-existence and exclusion relationships among the bacteria species involved in all the Daqu samples and in the LTD, MTD and HTD samples from a specific region were also identified. These results provide a better understanding of the bacterial diversity in different types of Daqu at the species level.

Characterizing the Contribution of Strain Specificity to the Microbiota Structure and Metabolites of Muqu and Fresh High-Temperature Daqu

In this study, the differences in physicochemical properties, microbial community structure, and metabolic characteristics between various fortified Muqu and their corresponding high-temperature Daqu (HTD) were investigated using multiphase detection methods. The results demonstrated that the physicochemical properties, community structure, dominant bacterial composition, and metabolic components varied significantly among the different types of fortified HTD. The differences between HTDs became more pronounced when fortified HTD was used as Muqu. Compared to HTD, Muqu exhibited a more complex volatile profile, while HTD contained higher levels of characteristic non-volatile components. The cultivable bacteria count in Muqu was significantly higher than that in HTD, while the cultivable fungi count was slightly lower than that in HTD. The fungal profiles in HTD were primarily associated with starch hydrolysis and ethanol synthesis, while bacterial activity was more prominent in Muqu. Additionally, pyrazine synthesis was mainly attributed to fungi in Muqu and bacteria in HTD. Source Tracker analysis indicated that 8.11% of the bacteria and 26.76% of the fungi originated from Muqu. This study provides a theoretical foundation for the controlled production of HTD, contributing to improvements in its quality and consistency.

Revealing the comprehensive effect of mechanization on sauce-flavor Daqu through high-throughput sequencing and multi-dimensional metabolite profiling

Mechanization has emerged as a focal point in the modernization of traditional enterprises, offering standardized production and labor reduction benefits. However, little is known about how mechanization affects the microbiota and metabolite profiles of Daqu. To address this gap, we conducted a comprehensive comparison between traditional and mechanical sauce-flavor Daqu using a multi-omics approach. Results showed that mechanical Daqu exhibited higher acidity, amino acid nitrogen and enzyme activity, alongside lower fat and moisture levels. Following mechanization, lactic acid bacteria (LAB), Staphylococcus, Aspergillus and Saccharomycopsis were enriched and identified as biomarkers, whereas Oceanobacillus, Monascus and Scopulariopsis were notably decreased. Furthermore, significant disparities in metabolic profiles were observed between the two types of Daqu based on GC-MS, GC-IMS, and LC-MS/MS analyses. The content of volatile compounds was significantly higher in mechanical Daqu (332.82 ± 22.69 mg/kg), while that of non-volatile compounds was higher in traditional Daqu (753.44 ± 41.82 mg/kg). Moreover, OPLS-DA models identified 44 volatile and 31 non-volatile compounds as differential metabolites. Multivariate statistical analysis indicated that bacteria and fungi primarily contributed to protease and saccharification activities, respectively. Additionally, the co-occurrence network revealed that Oceanobacillus and Scopulariopsis were closely associated with non-volatile compound formation, while LAB and Rhizopus significantly influenced volatile compound production. These findings elucidate the multi-dimensional relationship between mechanization and Daqu quality, offering insights to advance the modernization of traditional industries.

Strengthening the microbial community and flavor structure of jiupei by simulating strong-aroma baijiu fermentation with Bacillus velezensis DQA21

BACKGROUND

Bacillus velezensis DQA21 is a functional strain used in the fermentation process of strong-aroma baijiu; however, its specific role in the process is still unclear.

RESULTS

In this study, specific roles of B. velezensis DQA21 in the fermentation process were explored. Bioaugmentation of B. velezensis DQA21 increased the diversity and abundance of the bacterial community during the first 32 days of fermentation and significantly inhibited the diversity and richness of the fungal community during days 12 to 32. According to cluster analysis, changes in the microbial community structure were observed during fermentation, and the fermentation process could be divided into two stages: stage I, days 0-12; and stage II, days 12-45. Additionally, the microbial community structures during the two fermentation stages were significantly different. Co-occurrence analysis showed that bioaugmentation with Bacillus increased the correlation between microorganisms in jiupei and had a significant impact on the overall network structure of the microbial community. In addition, Bacillus significantly increased the production of flavor substances in jiupei, causing the total esters, total alcohols, and total acids contents to increase by 19.1%, 81.1%, and 25.9% respectively.

CONCLUSION

The results suggested that bioaugmentation with B. velezensis DQA21 had a strong impact on the microbial community structure in strong-aroma baijiu, enhancing the volatile flavor components. Additionally, the work also provides a better understanding on the effect of augmentation on the microbial community in jiupei, which could help better regulation of solid-state fermentation in strong-aroma baijiu. © 2024 Society of Chemical Industry.

Deciphering the core microbes and their interactions in spontaneous Baijiu fermentation: A comprehensive review

The spontaneous Baijiu fermentation system harbors a complex microbiome that is highly dynamic in time and space and varies depending on the Jiuqu starters and environmental factors. The intricate microbiota presents in the fermentation environment is responsible for carrying out various reactions. These reactions necessitate the interaction among the core microbes to influence the community function, ultimately shaping the distinct Baijiu styles through the process of spontaneous fermentation. Numerous studies have been conducted to enhance our understanding of the diversity, succession, and function of microbial communities with the aim of improving fermentation manipulation. However, a comprehensive and critical assessment of the core microbes and their interaction remains one of the significant challenges in the Baijiu fermentation industry. This paper focuses on the fermentation properties of core microbes. We discuss the state of the art of microbial traceability, highlighting the crucial role of environmental and starter microbiota in the Baijiu brewing microbiome. Also, we discuss the various interactions between microbes in the Baijiu production system and propose a potential conceptual framework that involves constructing predictive network models to simplify and quantify microbial interactions using co-culture models. This approach offers effective strategies for understanding the core microbes and their interactions, thus beneficial for the management of microbiota and the regulation of interactions in Baijiu fermentation processes.

Pediococcus spp.-mediated competition interaction within Daqu microbiota determines the temperature formation and metabolic profiles

Fermented microbiota is critical to the formation of microenvironment and metabolic profiles in spontaneous fermentation. Microorganisms generate a diverse array of metabolites concurrent with the release of heat energy. In the case of Daqu fermentation, the peak temperature exceeded 60°C, forming a typical high-temperature fermentation system known as high-temperature Daqu. However, microorganisms that cause the quality variation in Daqu and how they affect the functional microbiota and microenvironment in the fermentation process are not yet clear. This study adopted high-throughput sequencing and monitored the dynamic fluctuations of metabolites and environmental factors to identify the pivotal microorganism responsible for the alterations in interaction patterns of functional keystone taxa and quality decline in the fermentation system of different operational areas during the in situ fermentation process that had been mainly attributed to operational taxonomic unit (OTU)_22 (Pediococcus acidilactici). Additionally, we used isothermal microcalorimetry, plate inhibition experiments, and in vitro simulation fermentation experiments to explore the impact of Pediococcus spp. on heat generation, microorganisms, and metabolite profiles. Results showed the heat peak generated by Pediococcus spp. was significantly lower than that of Bacillus spp., filamentous fungi, and yeast. In addition, the preferential growth of P. acidilactici strain AA3 would obviously affect other strains to colonize through competition, and its metabolites made a significant impact on filamentous fungi. The addition of P. acidilactici strain AA3 in simulated fermentation would cause the loss of pyrazines and acids in metabolites. These evidences showed that the overgrowth of Pediococcus spp. greatly influenced the formation of high temperatures and compounds in solid-state fermentation systems. Our work illustrated the vital impact of interaction variability mediated by Pediococcus spp. for microbial assembly and metabolites, as well as in forming temperature. These results emphasized the functional role of Daqu microbiota in metabolites and heat production and the importance of cooperation in improving the fermentation quality.IMPORTANCEThe stable and high-quality saccharifying and fermenting starter in traditional solid-state fermentation was the prerequisite for liquor brewing. An imbalance of microbial homeostasis in fermentation can adversely impact production quality. Identification of such critical microorganisms and verifying their associations with other fermentation parameters pose a challenge in a traditional fermentation environment. To enhance the quality of spontaneous fermented products, strategies such as bioaugmentation or the control of harmful microorganisms would be employed. This work started with the differences in high-temperature Daqu metabolites to explore a series of functional microorganisms that could potentially contribute to product disparities, and found that the differences in interactions facilitated directly or indirectly by Pediococcus spp. seriously affected the development of microbial communities and metabolites, as well as the formation of the microenvironment. This study not only identified functional microbiota in Daqu that affected fermentation quality, but also demonstrated how microorganisms interact to affect the fermentation system, which would provide guidance for microbial supervision in the actual production process. Besides, the application of isothermal microcalorimetry in this study was helpful for us to understand the heat production capacity of microorganisms and their adaptability to the environment. This study presented a commendable framework for improving and controlling the quality of traditional fermentation and inspired further investigations in similar systems.

Revealing the influence of exogenously inoculated Bacillus spp. on the microbiota and metabolic potential of medium-temperature Daqu: A meta-omics analysis

To determine the unique contribution of the bioturbation to the properties of the medium-temperature Daqu, we investigated the differences in microbiota and metabolic composition using the meta-omics approach. Bioturbation increased the amounts of microbial specie and influenced the contribution of the core microbiota to the metabolome. Specifically, inoculated synthetic microbiota (MQB) enhanced the abundance of Bacillus amyloliquefaciens, while Bacillus licheniformis (MQH) increased the abundance of the two Aspergillus species and four species level of lactic acid bacteria. These changes of the microbial profiles significantly increased the potentials of carbohydrate metabolism, amino acid metabolism, and biosynthesis of ester compounds. Consequently, both patterns significantly increased the content of volatile compounds and free amino acids, which were 27.61% and 21.57% (MQB), as well as 15.14% and 17.83% (MQH), respectively. In addition, the contents of lactic acid in MQB and MQH decreased by 65.42% and 42.99%, respectively, closely related to the up- or down-regulation of the expression of their corresponding functional enzyme genes. These results suggested that bioturbation drove the assembly of the core microbiota, rather than becoming critical functional species. Overall, our study provides new insights into the functional role of exogenous isolates in the Daqu microecosystem.

Insight investigation into the response pattern of microbial assembly succession and volatile profiles during the brewing of sauce-flavor baijiu based on bioaugmentation

To improve the flavor profile and sensory quality of baijiu, the utilization of bioaugmented fermentation inoculated with functional microbiota normally serves as an effective method for directional regulation during the baijiu fermentation process. In this study, a systematic analysis of the succession patterns and volatile flavor compound profiles of microbial communities was carried out by high-throughput sequencing and solid-phase microextraction gas chromatography-mass spectrometry, respectively. The results demonstrated that the Saccharomyces cerevisiae YS222-related bioaugmentation clearly altered the microbial composition, particularly the assembly of bacteria, and promoted the quantity of the most volatile flavoring compounds, including alcohols, esters, and pyrazines. In addition, the correlation analysis showed that Saccharomyces and Lactobacillus in the augmented group were the main biomarkers associated with the dynamics of microbial community and greatly contributed to the brewing of sauce-flavor baijiu, which congruent with the outcomes of the enrichment analysis of integrated metabolic pathway. Thus, this work is beneficial for promoting the quality of baijiu and will serve as a useful reference for clarifying the possible mechanism of augmented fermentation on flavor development.

Predicting the final metabolic profile based on the succession-related microbiota during spontaneous fermentation of the starter for Chinese liquor making

Microbial inoculation is an effective way to improve the quality of fermented foods via affecting the microbiota structure. However, it is unclear how the inoculation regulates the microbiota structure, and it is still difficult to directionally control the microbiota function via the inoculation. In this work, using the spontaneous fermentation of the starter (Daqu) for Chinese liquor fermentation as a case, we inoculated different microbiota groups at different time points in Daqu fermentation, and analyzed the effect of the inoculation on the final metabolic profile of Daqu. The inoculated microbiota and inoculated time points both significantly affected the final metabolites via regulating the microbial succession (P < 0.001), and multiple inoculations can promote deterministic assembly. Twenty-seven genera were identified to be related to microbial succession, and drove the variation of 121 metabolites. We then constructed an elastic network model to predict the profile of these 121 metabolites based on the abundances of 27 succession-related genera in Daqu fermentation. Procrustes analysis showed that the model could accurately predict the metabolic abundances (average Spearman correlation coefficients >0.3). This work revealed the effect of inoculation on the microbiota succession and the metabolic profile. The established predicted model of metabolic profile would be beneficial for directionally improving the food quality.IMPORTANCEThis work revealed the importance of microbial succession to microbiota structure and metabolites. Multi-inoculations would promote deterministic assembly. It would facilitate the regulation of microbiota structure and metabolic profile. In addition, we established a model to predict final metabolites based on microbial genera related to microbial succession. This model was beneficial for optimizing the inoculation of the microbiota. This work would be helpful for controlling the spontaneous food fermentation and directionally improving the food quality.

Contribution of microorganisms from pit mud to volatile flavor compound synthesis in fermented grains for nongxiangxing baijiu brewing

BACKGROUND

Nongxiangxing baijiu (NB) is known for its distinct flavor profile, which is attributed to key aroma compounds. The exposed fermentation technique, utilizing daqu and solid-state fermentation in pit muds, plays a crucial role in flavor development. Though previous studies have investigated the impact of microorganisms from pit ?ud and fermented grains on flavor compound production, a comprehensive understanding of microbial functions in the entire pit fermentation system is lacking. Herein, we aimed to explore the role of pit-mud-derived microorganisms in shaping the microbial community and flavor compound synthesis in NB.

RESULTS

There are 76 volatile flavor compounds that have been identified in fermented grains during NB fermentation. The main flavor compounds in NB clustered within the same network module, and 27.27% of microorganisms in the core modules of the fermented grain co-occurrence network originated from pit mud. The relationship between pit mud microorganisms and flavor compounds revealed a significant positive correlation (92%). Notably, Prevotella and Sarocladium were identified as the main contributors to this effect on flavor.

CONCLUSION

Microorganisms originating from pit mud influenced the composition and activity of microorganisms in fermented grains and facilitated the production of flavor compounds in NB. © 2023 Society of Chemical Industry.

Seasonal dynamics of phyllosphere epiphytic microbial communities of medicinal plants in farmland environment

Introduction

The phyllosphere of plants is inhabited by various microorganisms, which play a crucial role in plant physiological metabolism. Currently, there is limited research on the dynamic effects of species and seasons on plant phyllosphere microbial community diversity and microbial interactions.

Methods

In this study, high-throughput sequencing technology was used to sequence the leaf surface parasitic microorganisms of five medicinal plants (Bupleurum chinense, Atractylodes lancea, Salvia miltiorrhiza, Astragalus membranaceus, and Lonicera japonica).

Results

The results showed that bacteria and fungi clustered into 3,898 and 1,572 operational taxonomic units (OTUs), respectively. Compared to host species, seasons had a more significant impact on the a diversity of bacteria and fungi. The heterogeneity of phyllosphere microbial communities was greater in winter compared to summer. Key species analysis at the OTU level and Spearman correlation analysis demonstrated significant preferences in microbial interactions under plant and seasonal backgrounds. The network connections between bacterial and fungal communities significantly increased during seasonal transitions compared to connections with plants.

Discussion

This study enhances our understanding of the composition and ecological roles of plant-associated microbial communities in small-scale agricultural environments. Additionally, it provides valuable insights for assessing the biodiversity of medicinal plants.

In-situ substitution and community dynamics modeling for enhanced safety in Chinese rice wine brewing

This research paper focuses on the application of the "Design-Build-Test-Learn" framework to design and evaluate a synthetic microbial community aimed at studying the impact of Lactic Acid Bacteria (LAB) interactions and fitness on the formation of biogenic amines (BAs) in Chinese rice wine (CRW). The study reveals a close correlation between the assembly model of LAB and the accumulation of BAs in CRW, and multiple interactions were observed between amine-producing and non-amine-producing LAB, including commensalism, amensalism, and competition. The commensalism among amine-producing LAB was found to promote BAs accumulation through metabolic cross-feeding of amino acids. Moreover, the higher-order interaction community was designed to regulate the BAs formation effectively. For instance, the interference of Lactiplantibacillus plantarum (ACBC271) resulted in the elimination of amine-producing LAB viability, resulting in a 22% decrease (not exceeding 43.54 mg/L) in the total amount of BAs. Simulation of community dynamics models further suggests that LAB with quantitative social interactions can effectively control LAB accumulation in CRW by forecasting fluctuation in BAs generation through fitness competition and metabolic interference. Overall, this study provides valuable insights into the complex interaction networks within microbial communities in traditional fermentation ecosystems. It also proposes a novel approach for quality control of nitrogen food safety factors in fermented foods.

Effect of Fortified Inoculation with Indigenous Lactobacillus brevis on Solid-State Fermentation of Light-Flavor Baijiu

Baijiu, one of the world's oldest distilled liquors, is widely consumed globally and has gained increasing popularity in East Asia. However, a comprehensive understanding of the underlying principles behind this traditional liquor product remains elusive. Currently, Baijiu is facing the industrial challenge of modernization and standardization, particularly in terms of food quality, safety, and sustainability. The current study selected a Lactobacillus brevis strain based on experiments conducted to assess its environmental tolerance, enzyme activity, and fermentation performance, and highlight its exceptional fermentation characteristics. The subsequent analysis focused on examining the effects of fortifying the fermentation process of L.brevis on key microbiotas, physicochemical parameters, and volatile profiles. The qPCR results revealed that the inoculated L. brevis strategically influenced the the composition of the dominant microbial communities by promoting mutual exclusion, ultimately leading to improved controllability of the fermentation process. Moreover, the metabolism of the inoculated L. brevis provided more compounds for the formation of flavor profiles during fermentation (the content of ethyl acetate was increased to 57.76 mg/kg), leading to a reduction in fermentation time (from 28 d to 21 d). These findings indicate promising potential for the application of the indigenous strain in Baijiu production.

Effect of inoculated Daqu on the spontaneous fermentation of Chinese liquor

Inoculated fermentation is widely used to improve the efficiency and quality of food production. However, it is still unclear how the inoculated multi-species starters influence food fermentation. Here we prepared two different types of Daqu, with/without the inoculation of Bacillus licheniformis in spontaneous Daqu fermentation, and studied their effects on liquor fermentation. These two types of Daqu were different in microbial community, and the inoculated Daqu had significantly higher relative abundance of Bacillus (69.2%) and lower relative abundance of Lactobacillus (3.2%) than those of Daqu without inoculation (Bacillus, 13.5%; Lactobacillus, 14.0%). After using with these two types of Daqu, metatranscriptomic analysis revealed that Kazachstania, Naumovozyma, Saccharomyces, Nakaseomyces and Lactobacillus were the transcriptional active genera during liquor fermentation. The transcription of Lactobacillus decreased on days 10 and 20 in liquor fermentation with the inoculated Daqu. The transcription of Kazachstania, Naumovozyma and Saccharomyces decreased on day 10 but increased on day 20 with the inoculated Daqu. Although lactate dehydrogenase decreased in Lactobacillus, alcohol dehydrogenase, aldehyde dehydrogenase and lactate dehydrogenase increased in Saccharomyces on day 20 in fermentation with inoculated Daqu, it indicated an extended succession of Saccharomyces in liquor fermentation. This would facilitate the increase of ethanol, acetic acid and lactic acid contents in liquor fermentation with inoculated Daqu. This work would be beneficial for improving Chinese liquor fermentation.

Improving the aroma profile of inoculated fermented sausages by constructing a synthetic core microbial community

Commercial starter cultures play a critical role in the industrial production of fermented sausages. However, commercial starter cultures could not reproduce the metabolic actions of diverse microorganisms and the aroma profile of the traditional spontaneously fermented sausages. Identifying the core microbial community in spontaneously fermented sausages will facilitate the construction of a synthetic microbial community for reproducing metabolic actions and flavor compounds in spontaneously fermented sausages. This study aimed to reveal the core microbial community of spontaneously fermented sausages based on their relative abundance, flavor-producing ability, and co-occurrence performance. We identified five promising genera to construct the synthetic core microbial community, these were Lactobacillus, Staphylococcus, Macrococcus, Streptococcus, and Pediococcus. Sausages inoculated with a synthetic core microbial community presented higher quality of aroma profile than the fermented sausages inoculated with a commercial starter culture. Some important volatile flavor compounds of spontaneously fermented sausage, such as (-)-β-pinene, β-caryophyllene, 3-methyl-1-butanol, α-terpineol, ethyl 2-methylpropanoate, and ethyl 3-methylbutanoate which are associated with floral, fruity, sweet, and fresh aromas, were also detected in fermented sausage inoculated with synthetic microbial community. This indicated that the synthetic core microbial community efficiently reproduced flavor metabolism. Overall, this study provides a practical strategy to design a synthetic microbial community applicable to different scientific fields.

Selection of initial microbial community for the alcoholic fermentation of sesame flavor-type baijiu

The initial microbial community is critical for the production of volatile metabolites during traditional food fermentations. Selection of the initial community plays an important role in improving the quality of fermented foods. Here, we used high-throughput amplicon sequencing combined with multivariate statistical methods to explore the microbial succession in stacking and alcoholic fermentation stages in sesame flavor-type baijiu making. We proposed a selection strategy for the initial microbial community in the alcoholic fermentation stage, which determined the quality of baijiu. Results suggested that the microbial composition statistically differed between stacking and alcoholic fermentation stages (ANOSIM, Bacteria: R = 0.60, P = 0.001; Fungi: R = 0.53, P = 0.001). Microbial succession drove metabolic succession (Bacteria: r = 0.87, P < 0.05; Fungi: r = 0.56, P < 0.05) in alcoholic fermentation. The fermentation time of stacking fermentation determined the initial community for alcoholic fermentation, and it can be used as a criterion for selection of the initial microbial community for alcoholic fermentation. The succession distance of the microbial community was varied and reached the highest (Bacteria: 0.048, Fungi: 0.064) at 30 h in stacking fermentation. When we selected 30 h as stacking fermentation time, the concentration (4.58 mg/kg) and diversity (0.61) of volatile metabolites were highest at the end of alcoholic fermentation. This work developed a succession distance-guided approach to select the initial microbial community for the alcoholic fermentation of sesame flavor-type baijiu. This approach can be used to improve the quality of baijiu.

Effect of lactic acid bacteria on the structure and potential function of the microbial community of Nongxiangxing Daqu

OBJECTIVES

The microbial community structure of the saccharifying starter, Nongxiangxing Daqu(Daqu), is a crucial factor in determining Baijiu's quality. Lactic acid bacteria (LAB), are the dominant microorganisms in the Daqu. The present study investigated the effects of LAB on the microbial community structure and its contribution to microbial community function during the fermentation of Daqu.

METHODS

The effect of LAB on the structure and function of the microbial community of Daqu was investigated using high-throughput sequencing technology combined with multivariate statistical analysis.

RESULTS

LAB showed a significant stage-specific evolution pattern during Daqu fermentation. The LEfSe analysis and the random forest learning algorithm identified LAB as vital differential microorganisms during Daqu fermentation. The correlation co-occurrence network showed aggregation of LAB and Daqu microorganisms, indicating LAB's significant position in influencing the microbial community structure, and suggests that LAB showed negative correlations with Bacillus, Saccharopolyspora, and Thermoactinomyces but positive correlations with Issatchenkia, Candida, Acetobacter, and Gluconobacter. The predicted genes of LAB enriched 20 functional pathways during Daqu fermentation, including Biosynthesis of amino acids, Alanine, aspartate and glutamate metabolism, Valine, leucine and isoleucine biosynthesis and Starch and sucrose metabolism, which suggested that LAB had the functions of polysaccharide metabolism and amino acid biosynthesis.

CONCLUSION

LAB are important in determining the composition and function of Daqu microorganisms, and LAB are closely related to the production of nitrogenous flavor substances in Daqu. The study provides a foundation for further exploring the function of LAB and the regulation of Daqu quality.

Comparative study on physicochemical properties, microbial composition, and the volatile component of different light flavor Daqu

Baijiu, a type of liquor, is known for its pure fragrance and softness. Its unique style is attributed to the complex microbial flora and flavor precursors found in Daqu. In order to elaborate the nature of light flavor Daqu to guide the baijiu production, four Daqu samples (DQ1, DQ2, DQ3, and DQ4) from Shanxi province were analyzed to determine their microbial structure, physicochemical properties, and volatile flavors using high-throughout put seqencing and headspace solid-phase microextraction/gas chromatography-mass spectrometry method in this study. The findings indicated that there were no noticeable variations in the water content and esterase activity of the four Daqu. However, the DQ2 sample had a higher acidity value and saccharifying enzyme activity, whereas DQ3 had the highest protease activity. The microbial community structure of the four Daqu was similar, with Lactobacillus and Streptophyta as the dominant bacteria, but the abundance of bacteria was different among the four Daqu. Issachenkia was a common dominant fungus genus in all samples. Rhizopus and Lichtemia were higher in DQ1 and DQ2, while Torulaspora, Aspergillus, and Candida were more prevalent in DQ4. A total of 27 volatile components were detected in the four Daqu, including esters, alcohols, ketones, aldehydes, and acids. DQ2 had the most volatile components and ethyl lactate and ethyl acetate were the most significant esters in the four samples. In conclusion, the physicochemical indicators of the four light flavor Daqu had distinct differences. There were significant variations in the abundance of bacteria and fungi, leading to differences in the volatile component content. These research findings can serve as a theoretical foundation for blending different light flavors Daqu and hold great significance in enhancing the quality of baijiu.

Enhancing Protease and Amylase Activities in Bacillus licheniformis XS-4 for Traditional Soy Sauce Fermentation Using ARTP Mutagenesis

This study was conducted to increase the enzymatic activity of Bacillus licheniformis XS-4, which was isolated from the traditional fermented mash of Xianshi soy sauce. The mutation was induced by atmospheric and room-temperature plasma (ARTP), and a mutant strain, mut80, was obtained. mut80 exhibited significant increases in protease and amylase activity by 90.54% and 143.10%, respectively, and the enhanced enzymatic activities were stably maintained after 20 consecutive incubations. Re-sequencing analysis of mut80 revealed that the mutation sites were located in 1518447(AT-T) and 4253106(G-A) in its genome, which was involved in the metabolic pathways of amino acids. The expression of the protease synthetic gene (aprX) increased 1.54 times, while that of the amylase gene (amyA) increased 11.26 times, as confirmed via RT-qPCR. Using ARTP mutagenesis, the present study proposes a highly efficient microbial resource with enhanced protease and amylase activity provided by B. licheniformis, which can potentially be used to improve the efficiency of traditional soy sauce fermentation.

Metaproteomic investigation of enzyme profile in daqu used for the production of Nongxiangxing baijiu

Enzymes and microbiota in daqu are essential for the brewing of Nongxiangxing baijiu. Uncover the key enzymes and functional strains in daqu is beneficial to improve the flavor and quality of Nongxiangxing baijiu. In this study, metaproteome technology was employed to determine the enzyme profiles in Nongxiangxing daqu, and strains with high saccharification activity were screened and identified. 933 proteins were identified in daqu, of which 463 belonged to enzymes, including 140 oxidoreductases, 98 transferases, 91 hydrolases, 49 ligases, 41 lyases and 27 isomerases, and hydrolase is the enzyme with the highest abundance in baijiu brewing. Among hydrolases, a total of 36 carbohydrate metabolism-related enzymes (CMEs) were identified, and 12 of them were key enzymes related to glycoside hydrolysis. Four major glycoside hydrolysis enzymes glucoamylase (EC 3.2.1.3), glucan 1,4-alpha-glucosidase (EC 3.2.1.3), glucanase (EC 3.2.1.-) and β-glucosidase (EC 3.2.1.21) were revealed, and their sources were Byssochlamys spectabilis, Lichtheimia ramosa and Thermoascus aurantiacus, respectively. Then, strains Aspergillus A2, A3, A7, Lichtheimia L1, L4, L5, and Saccharomycopsis S2, S4, S6 with high saccharifying enzyme-producing capacity were screened through culture-dependent approach. Resents presented in this study can further reveal the enzyme profiles and identify the main functional strains in daqu, which can provide theoretical support for the brewing of Nongxiangxing baijiu.

Unraveling multifunction of low-temperature Daqu in simultaneous saccharification and fermentation of Chinese light aroma type liquor

Chinese liquor is produced by a representative simultaneous saccharification and fermentation process. Daqu, as a starter of Chinese liquor fermentation, affects both saccharification and fermentation. However, it is still unclear how Daqu contributed to the simultaneous saccharification and fermentation process. Here, using Chinese light aroma type liquor as a case, we identified low-temperature Daqu-originated enzymes and microorganisms that contributed to the simultaneous saccharification and fermentation using metaproteomic analysis combined with amplicon sequencing analysis. α-Amylase and glucoamylase accounted for 95 % of total saccharifying enzymes and were identified as key saccharifying enzymes. Lichtheimia was the key producer of these two enzymes (> 90 %) in low-temperature Daqu. Daqu contributed 90 % α-amylase and 99 % glucoamylase to the initial liquor fermentation. These two enzymes decreased by 35 % and 49 % until day 15 in liquor fermentation. In addition, Daqu contributed key microbial genera (91 % Saccharomyces, 6.5 % Companilactobacillus) and key enzymes (37 % alcohol dehydrogenase, 40 % lactic acid dehydrogenase, 56 % aldehyde dehydrogenase) related with formations of ethanol, lactic acid and flavour compounds to the initial liquor fermentation. The average relative abundances of these fermentation-related key microorganisms and enzymes increased by 2.78 times and 1.29 times till day 15 in liquor fermentation, respectively. It indicated that Daqu provided saccharifying enzymes for starch hydrolysis, and provided both enzymes and microorganisms associated with formations of ethanol, lactic acid and flavour compounds for liquor fermentation. This work illustrated the multifunction of low-temperature Daqu in the simultaneous saccharification and fermentation of Chinese light aroma type liquor. It would facilitate improving liquor fermentation by producing high-quality Daqu.

Bacteria and filamentous fungi running a relay race in Daqu fermentation enable macromolecular degradation and flavor substance formation

As the saccharifying and fermentative agent, medium-temperature Daqu (MT-Daqu) plays an irreplaceable role in the production of strong-flavor Baijiu. Numerous studies have focused on the microbial community structure and potential functional microorganisms, however, little is known about the succession of active microbial community and the formation mechanism of community function during MT-Daqu fermentation. In this study, we presented an integrated analysis of metagenomics, metatranscriptomics, and metabonomics covering the whole fermentation process of MT-Daqu to reveal the active microorganisms and their participations in metabolic networks. The results showed that dynamic of metabolites were time-specific, and the metabolites and co-expressed active unigenes were further classified into four clusters according to their accumulation patterns, with members within each cluster displaying a uniform and clear pattern of abundance across fermentation. Based on KEGG enrichment analysis in co-expression clusters and succession of active microbial community, we revealed that Limosilactobacillus, Staphylococcus, Pichia, Rhizopus, and Lichtheimia were metabolically active members at the early stage, and their metabolic activities were conducive to releasing abundant energy to drive multiple basal metabolisms such as carbohydrates and amino acids. Thereafter, during the high temperature period and at the end of fermentation, multiple heat-resistant filamentous fungi were transcriptionally active populations, and they acted as both the saccharifying agents and flavor compound producers, especially aromatic compounds, suggesting their crucial contribution to enzymatic activity and aroma of mature MT-Daqu. Our findings revealed the succession and metabolic functions of the active microbial community, providing a deeper understanding of their contribution to MT-Daqu ecosystem.

Plant species shape the bacterial communities on the phyllosphere in a hyper-arid desert

Microorganisms are an important component of global biodiversity. However, they are vulnerable to hyper-arid climates in desert regions. Xerophytes are desert vegetation with unique biodiversity. However, little is known about the identities and communities of phyllosphere epiphytic microorganisms inhabiting the xerophyte leaf surface in the hot and dry environment. The diversity and community composition of phyllosphere epiphytes on different desert plants in Gansu, China, was investigated using the next-generation sequencing technique, revealing the diversity and community composition of the phyllosphere epiphytic bacteria associated with desert xerophytes. In addition, the ecological functions of the bacterial communities were investigated by combining the sequence classification information and prokaryotic taxonomic function annotation (FAPROTAX). This study determined the phyllosphere bacterial community composition, microbial interactions, and their functions. Despite harsh environments in the arid desert, we found that there are still diverse epiphytic bacteria on the leaves of desert plants. The bacterial communities mainly included Actinobacteria (52.79%), Firmicutes (31.62%), and Proteobacteria (12.20%). Further comparisons revealed different microbial communities, including Firmicutes at the phylum and Paenibacillaceae at the family level, in the phyllosphere among different plants, suggesting that the host plants had strong filter effects on bacteria. Co-occurrence network analysis revealed positive relationships were dominant among different bacterial taxa. The abundance of Actinobacteria and Proteobacteria was positively correlated, demonstrating their mutual relationship. On the other hand, the abundance of Firmicutes was negatively correlated, which suggested that they inhibit the growth of other bacterial taxa. FAPROTAX prediction revealed that chemoheterotrophy (accounting for 39.02% of the community) and aerobic chemoheterotrophy (37.01%) were the main functions of the leaf epiphytic bacteria on desert plants. This study improves our understanding of the community composition and ecological functions of plant-associated microbial communities inhabiting scattered niches in the desert ecosystem. In addition, the study provides insight into the biodiversity assessment in the desert region.

Exploration of microbiome diversity of stacked fermented grains by flow cytometry and cell sorting

Sauce-flavor baijiu is one of the twelve flavor types of Chinese distilled fermented product. Microbial composition plays a key role in the stacked fermentation of Baijiu, which uses grains as raw materials and produces flavor compounds, however, the active microbial community and its relationship remain unclear. Here, we investigated the total and active microbial communities of stacked fermented grains of sauce-flavored Baijiu using flow cytometry and high-throughput sequencing technology, respectively. By using traditional high-throughput sequencing technology, a total of 24 bacterial and 14 fungal genera were identified as the core microbiota, the core bacteria were Lactobacillus (0.08-39.05%), Acetobacter (0.25-81.92%), Weissella (0.03-29.61%), etc. The core fungi were Issatchenkia (23.11-98.21%), Monascus (0.02-26.36%), Pichia (0.33-37.56%), etc. In contrast, using flow cytometry combined with high-throughput sequencing, the active dominant bacterial genera after cell sorting were found to be Herbaspirillum, Chitinophaga, Ralstonia, Phenylobacterium, Mucilaginibacter, and Bradyrhizobium, etc., whereas the active dominant fungal genera detected were Aspergillus, Pichia, Exophiala, Candelabrochaete, Italiomyces, and Papiliotrema, etc. These results indicate that although the abundance of Acetobacter, Monascus, and Issatchenkia was high after stacked fermentation, they may have little biological activity. Flow cytometry and cell sorting techniques have been used in the study of beer and wine, but exploring the microbiome in such a complex environment as Chinese baijiu has not been reported. The results also reveal that flow cytometry and cell sorting are convenient methods for rapidly monitoring complex microbial flora and can assist in exploring complex environmental samples.

Acidity drives volatile metabolites in the spontaneous fermentation of sesame flavor-type baijiu

Environmental factors play an important role in contributing to intricate compositional dynamics and volatile metabolites in food fermentation. However, our understanding of which and how environmental factors affect volatile metabolites during sesame flavor-type baijiu fermentation is poor. Here, we examined the effects of environmental factors on the bacterial and fungal community to determine how changes in representative factors impact the microbial structure, diversity, and volatile metabolites in three fermentations. Results showed that bacterial community (ANOSIM: R = 0.79, P = 0.001), fungal community (ANOSIM: R = 0.65, P = 0.001), and volatile metabolites (ANOSIM: R = 0.84, P = 0.001) were significantly different in three fermentations. Acidity, ethanol, and moisture negatively impacted bacterial composition and diversity (P < 0.05). The fungal diversity and structure were positively and significantly affected by acidity (path coefficient, b = 0.54 for diversity, b = 0.35 for structure, P < 0.05). The fungal community rather than the bacterial community was the strongest driver of volatile metabolites. Fungal structure and diversity were equally important for the composition and content of volatile metabolites (structure: b = 0.50, diversity: b = 0.56, P < 0.05). 66 % of variations in volatile metabolites could be explained. Altogether these results indicated that acidity strongly drove volatile metabolites by modulating fungal structure and diversity. This work provides insights into managing volatile metabolites by regulating initial acidity in sesame flavor-type baijiu fermentation.

The microbial diversity and flavour metabolism of Chinese strong flavour Baijiu: a review

Strong flavour Baijiu is widely consumed in China and is produced by the fermentation of grains using microbial starters. However, a comprehensive understanding of the diversity and metabolic characteristics of microbial communities involved in the solid-state fermentation of Baijiu is important for determining the relationship between microbial composition, flavour metabolism and understanding Baijiu fermentation conditions. Although studies have examined the metabolic pathways and impact of major processes on flavour compounds in strong flavour Baijiu, aspects of the fermentation process remain unexplored. In this review, methods are discussed for the optimisation of microbial diversity in strong flavour Baijiu and associated effects on the flavour of Baijiu. Recent studies are reviewed on starters (Daqu), fermented grains (Jiupei), and pit mud together with the effects of microbial composition on the quality of strong flavour Baijiu. The challenges of Baijiu research and production are discussed, including the role of the microbial diversity of Daqu and Jiupei in the flavour composition of strong flavour Baijiu. This review contributes to the current understanding of processing strong flavour Baijiu and serves as a reference for screening flavour related microorganisms, which is valuable for improving the quality of strong flavour Baijiu.

Effects of microbial interspecies relationships and physicochemical parameters on volatile flavors in sorghum-based fermented grains during the fermentation of Shanxi light-flavored liquor

In this study, high-throughput technology was used to reveal the core microbial community in sorghum-based fermented grains during different fermentation periods and to quantify the impacts of physicochemical parameters and microbial interspecies relationships on the volatile flavors. Headspace solid-phase microextraction, coupled with gas chromatography-mass spectrometry, was used to select 14 major volatile products with relative content greater than 1% in at least one sample, including three alcohols, one acid, eight esters, and two alkanes. The relative content of alkanes was only high on the first day and continued to decrease during the later fermentation stage. As fermentation progressed, the relative content of ethanol, ethyl acetate (aroma), and isoamyl alcohol (pungent, spicy) first increased and then decreased. In addition, the relative content of other ethyl esters continued to increase. In the early stage of fermentation (1-7 days), the temperature, moisture, and alcohol content showed an upward trend, while the content of reducing sugar decreased. As the temperature decreased in the middle and later stages (7-28 days), the physicochemical parameters tended to stabilize. In community composition, the dominant bacterial genera were Lactobacillus, Streptomyces, and Acetobacter, and the fungal genera were mainly Issatchenkia, Torulaspora, and Pichia. Network analysis identified a total of 10 core microbiota as the main contributors of esters and alkane metabolites. Moreover, total acidity and reducing sugar played important roles in promoting the formation of core microbiota and succession of dominant taxa.

Difference of microbial community and gene composition with saccharification function between Chinese nongxiangxing daqu and jiangxiangxing daqu

BACKGROUND

The saccharification function of daqu is usually characterized by two indicators: saccharification power and liquefaction power. Daqu provides diverse microbial saccharifying enzymes for hydrolyzing carbohydrate in Baijiu fermenting grain. Obviously, the composition of microbial communities and enzymatic genes in different types of daqu cultured at varied temperatures is different. However, these differences in saccharification function are not fully understood.

RESULTS

The findings suggested that the saccharification power and liquefaction power of jiangxiangxing daqu were lower than those of nongxiangxing daqu throughout the production process. We employed metagenomics to find evidence that a mode of multiple saccharifying enzymes involving amylase, cellulase and hemicellulase originating from various microbes exists in daqu. Moreover, a totality of 541 related differential genes were obtained, some of which, annotated to genera of Aspergillus, Lactobacillus and Weissella, were significantly enriched (P < 0.05) in nongxiangxing daqu, while others, annotated to thermophilic genera of Virgibacillus, Bacillus, Kroppenstedtia and Saccharopolyspora, showed a higher relative abundance in jiangxiangxing daqu (P < 0.05).

CONCLUSION

Various microbial communities of daqu showed diverse saccharification capacity during cultivation of different parameters. These findings are helpful in comprehending the saccharification functional genes of daqu. © 2022 Society of Chemical Industry.

Functional microorganisms in Baijiu Daqu: Research progress and fortification strategy for application

Daqu is a saccharifying and fermenting starter in the production of Chinese Baijiu; its quality directly affects the quality of Baijiu. The production of Daqu is highly environment-dependent, and after long-term natural domestication, it is rich in a wide variety of microorganisms with a stable composition, which provide complex and diverse enzymes and flavor (precursor) substances and microbiota for Jiupei (Fermented grains) fermentation. However, inoculation with a relatively stable microbial community can lead to a certain upper limit or deficiencies of the physicochemical properties (e.g., saccharification capacity, esterification capacity) of the Daqu and affect the functional expression and aroma formation of the Daqu. Targeted improvement of this problem can be proposed by selecting functional microorganisms to fortify the production of Daqu. This review introduced the isolation, screening, identification and functional characteristics of culture-dependent functional microorganisms in Baijiu-brewing, the core functional microbiota community of Daqu, and the related research progress of functional microorganisms fortified Daqu, and summarized the fortifying strategies of functional microorganisms, aiming to further deepen the application of functional microorganisms fortification in Daqu fermentation and provide ideas for the flavor regulation and quality control of Baijiu.

Mechanism of Enhancing Pyrazines in Daqu via Inoculating Bacillus licheniformis with Strains Specificity

Despite the importance of pyrazines in Baijiu flavor, inoculating functional strains to increase the contents of pyrazine in Daqu and how those interact with endogenic communities is not well characterized. The effects of inoculating Bacillus licheniformis with similar metabolic capacity on pyrazine and community structure were assessed in the Daqu complex system and compared with traditional Daqu. The fortification strategy increased the volatile metabolite content of Daqu by 52.40% and the pyrazine content by 655.99%. Meanwhile, results revealed that the pyrazine content in Daqu inoculated isolate J-49 was 2.35-7.41 times higher than isolate J-41. Both isolates have the almost same capability of 2,3-butanediol, a key precursor of pyrazine, in pure cultured systems. Since the membrane fatty acids of isolate J-49 contain unsaturated fatty acids, it enhances the response-ability to withstand complex environmental pressure, resulting in higher pyrazine content. PICRUSt2 suggested that the increase in pyrazine was related to the enzyme expression of nitrogen metabolism significantly increasing, which led to the enrichment of NH4⁺ and 2,3-butanediol (which increased by 615.89%). These results based on multi-dimensional approaches revealed the effect of functional bacteria enhancement on the attribution of Daqu, laid a methodological foundation regulating the microbial community structure and enhanced the target products by functional strains.

Integrated microRNA and transcriptome profiling reveals the regulatory network of embryo abortion in jujube

Hybridization is an important approach to the production of new varieties with exceptional traits. Although the kernel rate of wild jujube (Ziziphus jujuba Mill. var. spinosa Hu.) is generally high, that of cultivated jujube (Z. jujuba Mill.) is low, greatly hampering the jujube breeding process. However, the mechanism by which this trait changed during jujube domestication remains unclear. Here, we explored the potential regulatory network that governs jujube embryo abortion using correlation analysis of population traits, artificial pollination, sugar content measurements and multi-omics analysis. The results showed that embryo abortion was an important reason for the low kernel rate of cultivated jujube, and kernel rate was negatively correlated with edible rate. Twenty-one days after pollination was a critical period for embryo abortion. At this time, the sugar content of cultivated 'Junzao' kernels decreased significantly compared with that of the pulp, but sugar content remained relatively stable in kernels of wild 'Suanzao'. A total of 1142 differentially expressed genes targeted by 93 microRNAs (miRNAs) were identified by transcriptome, miRNA and degradome sequencing, and may be involved in the regulation of embryo abortion during kernel development. Among them, DELLA protein, TCP14 and bHLH93 transcription factors have been shown to participate in the regulation of embryonic development. Our findings suggest that carbohydrate flow between different tissues of cultivated jujube exhibits a bias toward the pulp at 21 days after pollination, thereby restricting the process of kernel development. This information enhances our understanding of the embryo abortion process and reveals miRNA-target gene pairs that may be useful for molecular-assisted breeding.

The differences in carbohydrate utilization ability between six rounds of Sauce-flavor Daqu

Sauce-flavor Daqu is an important source of fermentation power in baijiu brewing. Revealing carbohydrate metabolism will help to explore the underlying reasons for the difference in fermentation performance of Daqu. In this study, metagenomic and metaproteomic technologies were performed to explore the carbohydrate metabolism network and its active functional microorganisms of Sauce-flavor Daqu. The sugar profile was analyzed using LC-MS to confirm the metabolic network. The results showed that 23 fungi and 5 bacteria were involved in carbohydrate metabolism. Starch metabolism, cellulose metabolism, and glucan metabolism were the main metabolic pathways, in which fungi especially Aspergillus were more involved than bacteria. Among these active microorganisms, Saccharomycopsis fibuligera, Aspergillus oryzae, Monascus purpureus, Byssochlamys spectabilis, Lichtheimia ramosa, Thermomyces lanuginosus, and Thermoascus aurantiacus were significant functional microorganisms with the ability to produce multiple enzymes. Lichtheimia ramosa, Lichtheimia corymbifera and Kroppenstedtia eburnea were biomarkers of Daqu in the first round, granting it a better liquefaction ability. β-amylase derived from wheat also played an important role in starch degradation, and the synergistic effect with α-amylase endowed Daqu with higher liquefaction power in the first two rounds. The results of this study are of great significance for the analysis of the mechanism of Daqu fermentation and provide a reliable theoretical basis for strengthening the fermentation performance of Daqu.

Analysis of the Microbial Community Structure and Volatile Metabolites of JIUYAO in Fangxian, China

JIUYAO is an important saccharification starter in the production of huangjiu and is also an important source of flavor. In this study, the microbial community structure of JIUYAO from Fangxian was studied by high-throughput sequencing (HTS) technology for the first time. The volatile flavor compounds of the JIUYAO metabolites were also analyzed by headspace solid-phase microextraction combined with full two-dimensional gas chromatography-mass spectrometry (HS-SPME-GC×GC/MS) for the first time. The results showed that there were 15 dominant bacterial genera, including Weissella, Pediococcus, unclasssified_k_norank_d_Bacteria, Lactobacillus, Leuconostoc, etc. Thirteen species of dominant fungi included Wickerhamomyces, Saccharomycopsis, Rhizopus, etc. The different samples of JIUYAO were similar in their microbial species, but the number of species was significantly different. A total of 191 volatile flavor compounds (VFCs) were detected, among which esters, alcohols, acids, and alkenes were the main flavor compounds, and 21 terpenoids were also detected. In addition, the functional prediction of micro-organisms in JIUYAO revealed that global and overview maps, amino acid metabolism, and carbohydrate metabolism were the dominant categories. Through correlation analysis, 538 potential correlations between the dominant micro-organisms and the different flavor compounds were obtained. This study revealed the interactions between the micro-organisms and the volatile metabolites in JIUYAO, which provided reliable data for the analysis of the microbial community structure of Fangxian JIUYAO and provided theoretical support for the quality evaluation of JIUYAO.