Profiling the Clostridia with butyrate-producing potential in the mud of Chinese liquor fermentation cellar

Revealing microbiota characteristics and predicting flavor-producing sub-communities in Nongxiangxing baijiu pit mud through metagenomic analysis and metabolic modeling

The microorganisms of the pit mud (PM) of Nongxiangxing baijiu (NXXB) have an important role in the synthesis of flavor substances, and they determine attributes and quality of baijiu. Herein, we utilize metagenomics and genome-scale metabolic models (GSMMs) to investigate the microbial composition, metabolic functions in PM microbiota, as well as to identify microorganisms and communities linked to flavor compounds. Metagenomic data revealed that the most prevalent assembly of bacteria and archaea was Proteiniphilum, Caproicibacterium, Petrimonas, Lactobacillus, Clostridium, Aminobacterium, Syntrophomonas, Methanobacterium, Methanoculleus, and Methanosarcina. The important enzymes ofPMwere in bothGH and GT familymetabolism. A total of 38 high-quality metagenome-assembled genomes (MAGs) were obtained, including those at the family level (n = 13), genus level (n = 17), and species level (n = 8). GSMMs of the 38 MAGs were then constructed. From the GSMMs, individual and community capabilities respectively were predicted to be able to produce 111 metabolites and 598 metabolites. Twenty-three predicted metabolites were consistent with the metabonomics detected flavors and served as targets. Twelve sub-community of were screened by cross-feeding of 38 GSMMs. Of them, Methanobacterium, Sphaerochaeta, Muricomes intestini, Methanobacteriaceae, Synergistaceae, and Caloramator were core microorganisms for targets in each sub-community. Overall, this study of metagenomic and target-community screening could help our understanding of the metabolite-microbiome association and further bioregulation of baijiu.

Coordination between scientific and technological innovation and the high-quality development of Baijiu industry: The coupling and decoupling perspective

The Baijiu industry is a significant contributor to both the food industry and the light industry. Its high tax characteristics effectively promote the sustainable development of the regional economy. First, the evaluation index system of scientific and technological innovation (STI) and high-quality development of Baijiu industry (HQDBI) were constructed. The entropy-improved CRITIC method was used to measure the weights. Second, the coordination relationship and evolution trend of STI and HQDBI were explored using the coupling coordination model and the Tapio decoupling model. Then, the transfer law and key influencing factors were further investigated using the Markov chain and grey correlation, respectively. The main contribution is the dynamic evolution of the coupling and decoupling relationships from the perspective of multiple Baijiu provinces, and deeply depicts the coordination relationship and evolutionary trends of STI and HQDBI. The results show that: the spatial distribution of the coupling coordination degree shows high values in the east-west and low values in the north-south characteristics. In 2021, a pattern of coordinated development in Baijiu provinces has emerged along the Yangtze River basin. The decoupling state is mainly strong decoupling, but it remains poor in Shanxi. The coordination process is unstable and difficult to achieve leapfrog development. Coordination, sustainability and innovation environment have a greater impact on the coordination of subsystems.

Enrichment of a mixed syngas-converting culture for volatile fatty acids and methane production

The present study evaluated the production potential of CH4, carboxylic acids and alcohols from a mixed culture enriched using synthetic syngas. The influence of syngas concentration on the microbial community and products productivity and selectivity was investigated. The results demonstrated the enrichment of a mesophilic mixed culture capable of converting CO and H2 mainly to CH4 and acetate, along with butyrate. The selectivity values showed that acetate production was enhanced during the first cycle in all conditions tested (up to 20 %), while CH4 was the main product generated during following cycles. Concretely, CH4 selectivity remained unaffected by syngas concentration, reaching a stable value of 41.6 ± 2.0 %. On the other hand, butyrate selectivity was only representative at the highest syngas concentration and lower pH values (26.1 ± 5.8 %), where the H2 consumption was completely inhibited. Thus, pH was identified as a key parameter for both butyrate synthesis and the development of hydrogenotrophic activity.

Illuminating the Characteristics and Assembly of Prokaryotic Communities across a pH Gradient in Pit Muds for the Production of Chinese Strong-Flavor Baijiu

Pit mud (PM), as an important source of microorganisms, is necessary for Chinese strong-flavor baijiu (CSFB) production. Although it has been revealed that the PM prokaryotic community diversities are influenced by its quality, product area, ages, etc., the characteristics and assembly process of the prokaryotic community in PMs across a pH gradient are still unclear. In this study, the regular changes of α- and β-diversities of the prokaryotic community across a pH gradient in PMs were revealed, which could be divided into "stable", "relatively stable", and "drastically changed" periods. A total of 27 phyla, 53 classes, and 381 genera were observed in all given samples, dominated by Firmicutes, Bacteroidetes, Proteobacteria, Lactobacillus, Caproiciproducens, Proteiniphilum, etc. Meanwhile, the complexity of the network structure of the prokaryotic microbial communities is significantly influenced by pH. The community assembly was jointly shaped by deterministic and stochastic processes, with stochastic process contributing more. This study was a specialized report on elucidating the characteristics and assembly of PM prokaryotic communities across a pH gradient, and revealed that the diversity and structure of PM prokaryotic communities could be predictable, to some degree, which could contribute to expanding our understanding of prokaryotic communities in PM.

Effects of continuous low-speed biogas agitation on anaerobic digestion of high-solids pig manure: Performance and microbial community

This study aimed to investigate effects of continuous low-speed biogas agitation on the anaerobic digestion (AD) performance and microbial community of high-solids pig manure (total solids content of 10%). Our results reveal that at a biogas agitation intensity of 1.10 L/g feed VS/d, CH4 production increased by 16.67% compared to the non-agitated condition, the removal efficiency of H2S reached 63.18%, and the abundance of Methanosarcina was the highest. The presence of Hungateiclostridiaceae was associated with H2S concentrations. An increasing biogas agitation intensity led to an elevated pH and a decreased oxidation-reduction potential (ORP). Acetate concentrations, pH, and ORP values indicated changes in H2S concentrations. Sedimentibacter demonstrates the potential to indicate biogas agitation intensity and pH. We demonstrate that continuous low-speed biogas agitation effectively increases CH4 production and reduces H2S concentrations in AD of high-solids pig manure, offering a potential technical pathway for developing AD processes for high-solids pig manure, it also demonstrates that AD process can reduce the risk of pathogen and parasite transmission.

Analysis of the differences in physicochemical properties, volatile compounds, and microbial community structure of pit mud in different time spaces

Pit mud (PM) is among the key factors determining the quality of Nongxiangxing baijiu, a Chinese liquor. Microorganisms present inside PM are crucial for the unique taste and flavor of this liquor. In this study, headspace solid-phase microextraction was used in combination with gas chromatography and high-throughput sequencing to determine the volatile compounds and microbial community structure of 10- and 40-year PM samples from different spaces. The basic physicochemical properties of the PM were also determined. LEfSe and RDA were used to systematically study the PM in different time spaces. The physicochemical properties and ester content of the 40-year PM were higher than those of the 10-year PM, but the spatial distribution of the two years PM samples exhibited no consistency, except in terms of pH, available phosphorus content, and ester content. In all samples, 29 phyla, 276 families, and 540 genera of bacteria, including four dominant phyla and 20 dominant genera, as well as eight phyla, 24 families, and 34 genera of archaea, including four dominant phyla and seven dominant genera, were identified. The LEfSe analysis yielded 18 differential bacteria and five differential archaea. According to the RDA, the physicochemical properties and ethyl caproate, ethyl octanoate, hexanoic acid, and octanoic acid positively correlated with the differential microorganisms of the 40-year PM, whereas negatively correlated with the differential microorganisms of the 10-year PM. Thus, we inferred that Caproiciproducens, norank_f__Caloramatoraceae, and Methanobrevibacter play a dominant and indispensable role in the PM. This study systematically unveils the differences that affect the quality of PM in different time spaces and offers a theoretical basis for improving the declining PM, promoting PM aging, maintaining cellars, and cultivating an artificial PM at a later stage.

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.

Effects of iodine intake on gut microbiota and gut metabolites in Hashimoto thyroiditis-diseased humans and mice

Hashimoto thyroiditis (HT) is an organ-specific autoimmune disease linked to iodine intake. Emerging evidence highlights the gut microbiota's role in HT pathogenesis via the microbiota-gut-thyroid axis. However, the process through which iodine intake modifies the microbiota and triggers HT remains unclear. This study examines how iodine affects gut dysbiosis and HT, recruiting 23 patients with HT and 25 healthy individuals to assess gut microbiota composition and metabolic features. Furthermore, we establish a spontaneously developed thyroiditis mouse model using NOD.H-2h4 mice highlighting the influence of iodine intake on HT progression. The butanoate metabolism significantly differs between these two groups according to the enrichment results, and butyric acid is significantly decreased in patients with HT compared with those in healthy individuals. Gut dysbiosis, driven by excessive iodine intake, disrupts TH17/Treg balance by reducing butyric acid. In summary, iodine intake alters intestinal microbiota composition and metabolic changes influencing the microbiota-gut-thyroid axis.

Novel primers to identify a wider diversity of butyrate-producing bacteria

Butyrate-producing bacteria are a functionally important part of the intestinal tract flora, and the resulting butyric acid is essential for maintaining host intestinal health, regulating the immune system, and influencing energy metabolism. However, butyrate-producing bacteria have not been defined as a coherent phylogenetic group. They are primarily identified using primers for key genes in the butyrate-producing pathway, and their use has been limited to the Bacillota and Bacteroidetes phyla. To overcome this limitation, we developed functional gene primers able to identify butyrate-producing bacteria through the butyrate kinase gene, which encodes the enzyme involved in the final step of the butyrate-producing pathway. Genomes extracted from human and rat feces were used to amplify the target genes through PCR. The obtained sequences were analyzed using BLASTX to construct a developmental tree using the MEGA software. The newly designed butyrate kinase gene primers allowed to recognize a wider diversity of butyrate-producing bacteria than that recognized using currently available primers. Specifically, butyrate-producing bacteria from the Synergistota and Spirochaetota phyla were identified for the first time using these primers. Thus, the developed primers provide a more accurate method for researchers and doctors to identify potential butyrate-producing bacteria and deepen our understanding of butyrate-producing bacterial species.

Co-production of lactate and volatile fatty acids through repeated-batch fermentation of fruit and vegetable waste: Effect of cycle time and replacement ratio

In this study, repeated-batch fermentation was used to convert fruit and vegetable waste to lactate and volatile fatty acids (VFAs), which are essential carbon sources for medium-chain fatty acids (MCFAs) production. The effect of cycle time and replacement ratio on acidification in long-term fermentation was investigated. The results showed that they had a significant impact on product yield, productivity, and type of products. Considering the yield, productivity, and lactate/VFAs ratio, a replacement ratio of 30% and a cycle time of 2 d may be more suitable for further production of MCFAs. Its productivity and lactate/VFAs ratio were 4.07 ± 0.24 g/(L·d) and 5 ± 0.6, respectively. The lactic acid bacteria, such as Enterococcus (63%) and Lactobacillus (33%), stabilized in the reactor, resulting in the generation of both lactate and VFAs by heterolactic fermentation. The present study demonstrated a new strategy with the potential to recover high-value products from organic waste streams.

Difference Analysis of the Composition of Iron (Hydr)Oxides and Dissolved Organic Matter in Pit Mud of Different Pit Ages in Luzhou Laojiao and Its Implications for the Ripening Process of Pit Mud

Long-term production practice proves that good liquor comes out of the old cellar, and the aged pit mud is very important to the quality of Luzhou-flavor liquor. X-ray diffraction, Fourier transform ion cyclotron resonance mass spectrometry, and infrared spectroscopy were used to investigate the composition characteristics of iron-bearing minerals and dissolved organic matter (DOM) in 2-year, 40-year, and 100-year pit mud and yellow soil (raw materials for making pit mud) of Luzhou Laojiao distillery. The results showed that the contents of total iron and crystalline iron minerals decreased significantly, while the ratio of Fe(II)/Fe(III) and the content of amorphous iron (hydr)oxides increased significantly with increasing cellar age. DOM richness, unsaturation, and aromaticity, as well as lignin/phenolics, polyphenols, and polycyclic aromatics ratios, were enhanced in pit mud. The results of the principal component analysis indicate that changes in the morphology and content of iron-bearing minerals in pit mud were significantly correlated with the changes in DOM molecular components, which is mainly attributed to the different affinities of amorphous iron (hydr)oxides and crystalline iron minerals for the DOM components. The study is important for understanding the evolution pattern of iron-bearing minerals and DOM and their interactions during the aging of pit mud and provides a new way to further understand the influence of aged pit mud on Luzhou-flavor liquor production.

Microbial biogeography of pit mud from an artificial brewing ecosystem on a large time scale: all roads lead to Rome

IMPORTANCE

Baijiu is a typical example of how humans employ microorganisms to convert grains into new flavors. Mud cellars are used as the fermentation vessel for strong-flavor Baijiu (SFB) to complete the decomposition process of grains. The typical flavor of SFB is mainly attributed to the metabolites of the pit mud microbiome. China has a large number of SFB-producing regions. Previous research revealed the temporal profiles of the pit mud microbiome in different geographical regions. However, each single independent study rarely yields a thorough understanding of the pit mud ecosystem. Will the pit mud microbial communities in different production regions exhibit similar succession patterns and structures under the impact of the brewing environment? Hence, we conducted research in pit mud microbial biogeography to uncover the impact of specific environment on the microbial community over a long time scale.

Succession of microbial community of the pit mud under the impact of Daqu of Nongxiang Baijiu

Complex microbiomes of pit mud play significant roles in imbuing flavors and qualities of Nongxiang Baijiu during fermentation. However, pit mud microbial enrichment and succession is a long process that is also accompanied by aging. Development of high-quality artificial pit mud becomes an urgent problem. In this study, a new medium based on space (TK) Daqu was used to effectively enrich the dominant microorganisms in pit mud. The results showed that Caproiciproducens was the most preponderance in the cultures unadded Daqu, whereas Clostridium sensu stricto 12 was the most preponderance, followed by Caproiciproducens in the enrichment cultures added TK Daqu. It is worth noting that TK Daqu balanced the relative abundance of Caproiciproducens and Clostridium sensu stricto 12 in 100-year pit mud culture (S100), which was more conducive to the increase of methanogens. PICRUSt2 prediction results showed that hydrogenotrophic methanogens could promote the synthesis of caproic acid by using the product H2 as the metabolic substrate and increased significantly in the pit mud enrichment cultures with TK Daqu. The increase of lactate dehydrogenase (EC 1.1.1.27) content in S100 contributed to the degradation of lactic acid and the increase of caproic acid. Adding TK Daqu enrichment cultures is more conducive to the enrichment and metabolic balance of pit mud microorganisms.

Metagenomic insights into the microbiota involved in lactate and butyrate production and manipulating their synthesis in alfalfa silage

AIMS

Lactate and butyrate are important indicators of silage quality. However, the microorganisms and mechanisms responsible for lactate and butyrate production in silage are not well documented.

METHODS AND RESULTS

whole-metagenomic sequencing was used to analyse metabolic pathways, microbiota composition, functional genes, and their contributions to lactate and butyrate production in alfalfa silage with (SA) and without (CK) sucrose addition. Carbon metabolism was the most abundant metabolic pathway. We identified 11 and 2 functional genes associated with lactate and butyrate metabolism, respectively. Among them, D-lactate dehydrogenase (ldhA) and L-lactate dehydrogenase (ldhB) were most important for the transition between D/L-lactate and pyruvate and were primarily related to Lactobacillus in the SA group. The genes encoding L-lactate dehydrogenase (lldD), which decomposes lactate, were the most abundant and primarily associated with Enterobacter cloacae. Butyrate-related genes, mainly encoding butyryl-CoA: acetate CoA-transferase (but), were predominantly associated with Klebsiella oxytoca and Escherichia coli in the CK group.

CONCLUSIONS

Enterobacteriaceae and Lactobacillaceae were mainly responsible for butyrate and lactate formation, respectively.

Microbial Community Affects Daqu Quality and the Production of Ethanol and Flavor Compounds in Baijiu Fermentation

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.

Regulation of the autochthonous microbial community in excess sludge for the bioconversion of carbon dioxide to acetate without exogenic hydrogen

The autochthonous microbial community from excess sludge was regulated for enhanced conversion of CO₂ to acetate without exogenic H₂. It was interesting that the acetate-fed system exhibited a surprising performance to regulate the microbial community for a high acetate yield and selectivity. As a result, some hydrogen-producing bacteria (e.g., Proteiniborus) and acetogenic bacteria with the ability of CO₂ reduction were enriched by acetate feeding, 2-bromoethanesulfonate (BES) addition and CO₂ stress. When the selected microbial community was applied to convert CO₂, the accumulation of acetate was positively correlated to the concentration of yeast extract. Finally, the acetate yield reached up to 67.24 mM with a high product selectivity of 84 % in the presence of yeast extract (2 g/L) and sufficient CO₂ in semi-continuous culture for 10 days. This work should help get new insights into the regulation of microbial community for the efficient acetate production from CO₂.

Microbial community succession patterns and drivers of Luxiang-flavor Jiupei during long fermentation

Luxiang-flavor Baijiu is the mainstream of Baijiu production and consumption in China, and the microbial composition has a great influence on the flavor and quality of Baijiu. In this study, we combined multi-omics sequencing technology to explore the microbial composition, dynamics and metabolite changes of Luxiang-flavor Jiupei during long fermentation periods. The results showed that based on the interaction between environmental constraints and microorganisms, Jiupei microorganisms formed different ecological niches and functional differentiation, which led to the formation of Jiupei stable core microorganisms. The bacteria were mainly Lactobacillus and Acetobacter, and the fungi were mainly Kazachstani and Issatchenkia. Most bacteria were negatively correlated with temperature, alcohol and acidity, and for the fungi, starch content, reducing sugar content and temperature had the most significant effects on community succession. Macroproteomic analysis revealed that Lactobacillus jinshani had the highest relative content; microbial composition, growth changes and functions were more similar in the pre-fermentation period (0-18 days); microorganisms stabilized in the late fermentation period (24-220 days). The metabolome analysis revealed that the metabolites of the Jiupei changed rapidly from 18 to 32 days of fermentation, with a significant increase in the relative content of amino acids, peptides and analogs and a significant decrease in the relative content of sugars; the metabolites of the Jiupei changed slowly from 32 to 220 days of fermentation, with a stabilization of the content of amino acids, peptides and analogs. This work provides insights into the microbial succession and microbial drivers during the long-term fermentation of Jiupei, which have potential implications for optimizing production and improving the flavor of Baijiu.

Revealing mechanism of micro-aeration for enhancing volatile fatty acids production from swine manure

Micro-aeration is considered a new strategy for improving volatile fatty acids (VFAs) production of agricultural waste. This study investigated the effect and mechanism of micro-aeration of air and oxygen (O₂) on VFAs production from swine manure. The results showed that Air-micro-aeration had the most significant improvement effect, with the highest VFAs of 8.21 g/L, which was increased by 22.4%. Moreover, the mixing effects of different micro-aeration were limited, and the microbial communities significantly varied. Firmicutes and Bacteroidota were the dominant hydrolytic and acidogenic bacteria, and Air-micro-aeration preferentially promoted electron transfer activity and energy generation. Methanosarcina, Methanocorpusculum, and Methanobrevibacter can adapt to environmental changes according to their different oxygen tolerance, and the consumption and conversion of VFAs by methanogens were slow under Air-micro-aeration condition. This study revealed mechanism of micro-aeration for improving VFAs production from swine manure, providing a theoretical basis for micro-aeration regulation optimization.

Chemotaxis of Clostridium Strains Isolated from Pit Mud and Its Application in Baijiu Fermentation

Clostridium is the key bacteria that inhabits the pit mud in a fermentation cell, for the production of strong-flavor Baijiu. Its activities in the process of Baijiu fermentation is closely related to the niches of pit mud and cells. After multiple rounds of underground fermentation, Clostridium has been domesticated and adapted to the environment. The mechanisms of clostridia succession in the pit mud and how they metabolize nutrients present in grains are not clear. In this study, 15 Clostridium species including three firstly reported ones (Clostridium tertium, Clostridium pabulibutyricum and Clostridium intestinale) in strong-flavor Baijiu pit mud, were isolated from the pit mud. Eighty one percent of these Clostridium strains are motile, and most of them show chemotaxis to organic acids, glutathione, saccharides and lactic acid bacteria. In a simulated Baijiu fermentation system, Clostridium migrated from pit mud to fermented grains with the addition of chemokine lactic acid, resulting in the production of acetic acid and butyric acid. The results help to understand the succession mechanism of Clostridium in pit mud, and provide a reference for regulation of lactic acid level in fermented grains during Baijiu fermentation.

A new method for screening and culture of Clostridium from pit mud under non-anaerobic conditions

Strong-flavor Baijiu (SFB) is produced in complex fermentation in pits under ground. Clostridium producing hexanoic acid plays a key role in the flavor formation of SFB. The screening and culture for Clostridium are very difficult because of its strict anaerobic characteristics. In this study, electric field assisted screening (EFAS) was used to screen Clostridium from pit mud, and electric culture (EC) was used to cultivate Clostridium under non-anaerobic conditions. A strain with a high yield of hexanoic acid was screened and named as Clostridium sp. EFAS6. Under non-anaerobic conditions, it grew rapidly only near the cathode end in the EFAS device because of the low oxidation-reduction potential of that electrode. In the experiment of high-density culture in the EC device, the cell concentration reached 10⁶-10⁷. After energy consumption was calculated, the optimal loading voltage was found to be 10 V. In the application, the broth of Clostridium sp. EFAS6 increased the content of ethyl hexanoic in SFB. Under non-anaerobic conditions, the anaerobe was screened by EFAS and cultivated in high density by EC. The EFAS and EC could also be used for the screening and culture of other anaerobes under non-anaerobic conditions.

Metabolite-Based Mutualistic Interaction between Two Novel Clostridial Species from Pit Mud Enhances Butyrate and Caproate Production

Pit mud microbial consortia play crucial roles in the formation of Chinese strong-flavor baijiu's key flavor-active compounds, especially butyric and caproic acids. Clostridia, one of the abundant bacterial groups in pit mud, were recognized as important butyric and caproic acid producers. Research on the interactions of the pit mud microbial community mainly depends on correlation analysis at present. Interaction between Clostridium and other microorganisms and its involvement in short/medium-chain fatty acid (S/MCFA) metabolism are still unclear. We previously found coculture of two clostridial strains isolated from pit mud, Clostridium fermenticellae JN500901 (C.901) and Novisyntrophococcus fermenticellae JN500902 (N.902), could enhance S/MCFA accumulation. Here, we investigated their underlying interaction mechanism through the combined analysis of phenotype, genome, and transcriptome. Compared to monocultures, coculture of C.901 and N.902 obviously promoted their growth, including shortening the growth lag phase and increasing biomass, and the accumulation of butyric acid and caproic acid. The slight effects of inoculation ratio and continuous passage on the growth and metabolism of coculture indicated the relative stability of their interaction. Transwell coculture and transcriptome analysis showed the interaction between C.901 and N.902 was accomplished by metabolite exchange, i.e., formic acid produced by C.901 activated the Wood-Ljungdahl pathway of N.902, thereby enhancing its production of acetic acid, which was further converted to butyric acid and caproic acid by C.901 through reverse β-oxidation. This work demonstrates the potential roles of mutually beneficial interspecies interactions in the accumulation of key flavor compounds in pit mud. IMPORTANCE Microbial interactions played crucial roles in influencing the assembly, stability, and function of the microbial community. The metabolites of pit mud microbiota are the key to flavor formation of Chinese strong-flavor baijiu. So far, researches on the interactions of the pit mud microbial community have been mainly based on the correlation analysis of sequencing data, and more work needs to be performed to unveil the complicated interaction patterns. Here, we identified a material exchange-based mutualistic interaction system involving two fatty acid-producing clostridial strains (Clostridium fermenticellae JN500901 and Novisyntrophococcus fermenticellae JN500902) isolated from pit mud and systematically elucidated their interaction mechanism for promoting the production of butyric acid and caproic acid, the key flavor-active compounds of baijiu. Our findings provide a new perspective for understanding the complicated interactions of pit mud microorganisms.

Metatranscriptomics Unravel Composition, Drivers, and Functions of the Active Microorganisms in Light-Flavor Liquor Fermentation

The microbial community in the fermented pit determines the quantity and quality of light-flavor liquor. Genetic diversity and the potential functions of the microbial community are often analyzed by DNA-based omics sequencing. However, the features of the active microbial community have not been systematically studied. Here, metatranscriptomic analysis was performed to elucidate the active microbial composition, drivers, and their functions in light-flavor liquor fermentation. Bacterial genera, Lactobacillus, Streptococcus, Pediococcus, Thermotoga, and Faecalibacterium, and fungal genera, Saccharomyces, Talaromyces, Aspergillus, Clavispora, Rhizophagus, Cyberlindnera, and Wickerhamomyces, were the dominant active microorganisms during the fermentation process. Additionally, they dominated the three-stage fermentation successively. Redundancy analysis showed that pH, ethanol, moisture, and starch were the main driving forces of microbial succession. Among the genes for the respective carbohydrate-active enzyme families, those for the glycoside hydrolase family 23, the glycosyltransferase family 2, the carbohydrate-binding module family 50, the polysaccharide lyase family 4, the auxiliary activity family 1, and the carbohydrate esterase family 9 showed the highest expression level. Additionally, the highly expressed enzymes and their contributed microorganisms were found in the key KEGG pathways, including carbohydrate metabolism, energy metabolism, lipid metabolism, and amino acid metabolism. Based on these data, a functional model of carbohydrate hydrolysis, ethanol production, and flavor generation were proposed. Taken together, Saccharomyces, Lactobacillus, Wickerhamomyces, Pediococcus, Candida, and Faecalibacterium were suggested as the core active microorganisms. Overall, our findings provide new insights into the composition, drivers, and functions of the active microorganisms, which is crucial for improving the quality of light-flavor liquor. IMPORTANCE There is an urgent need for discovering the diversity and functions of the active microbial community in solid-state fermentation, especially in the pit of Chinese distilled liquor fermentation. Although the genetic composition of the microbial community has been clarified frequently by DNA-based sequencing, the composition and functions of the active microbial community have not been systematically revealed so far. Therefore, analysis of RNA-based data is crucial for discovering the functional microbial community. In this study, we employed metatranscriptomic analysis to elucidate the active microbial composition, successive drivers, and their functions in light-flavor liquor fermentation. The strategy can be broadly useful for discovering the active microbial community and exploring their functions in other types of flavor distilled liquor or other ecosystems. This study provides new insights into the understanding of the active microbial community composition and its functions.

Analysis of microbial community structure and volatile compounds in pit mud used for manufacturing Taorong-type Baijiu based on high-throughput sequencing

In this study, the pit mud used in manufacturing Taorong-type Baijiu was collected from the upper, middle, lower and bottom layers of pits at Henan Yangshao Liquor Co., LTD. High-throughput sequencing (HTS) technology was used to analyze the microbial community structure of the pit mud. In addition, the volatile compounds in the pit mud were subjected to preliminary qualitative analysis through headspace-solid phase microextraction and gas chromatography-mass spectrometry (GC-MS). The HTS results demonstrated that there were 5, 3, 5 and 5 dominant bacterial phyla (including 11, 11, 9 and 8 dominant bacterial genera) and 3, 3, 3 and 3 dominant fungal phyla (including 4, 7, 7 and 5 dominant fungal genera) in the pit mud from the F-S (upper), G-Z (middle), H-X (lower) and I-D (bottom) layers, respectively. In the qualitative analysis of the volatile compounds, a total of 77types of volatile compounds were detected in the pit mud, including 46, 45, 39 and 49 types in the pit mud from layers F-S, G-Z, H-X and I-D, respectively. Esters and acids were the two main components of the pit mud. The correlation between the microorganisms present and the main volatile compounds in the pit mud was analyzed. Lentimicrobium, Syner-01 and Blvii28_wastewater-sludge groups were found for the first time in pit mud used for manufacturing Taorong-type Baijiu. The findings of this study could provide a theoretical foundation for improving the quality of pit mud and the flavor of Taorong-type Baijiu.

Comparative Genomics Unveils the Habitat Adaptation and Metabolic Profiles of Clostridium in an Artificial Ecosystem for Liquor Production

Pit mud is a typical artificial ecosystem for Chinese liquor production. Clostridium inhabiting pit mud plays essential roles in the flavor formation of strong-flavor baijiu. The relative abundance of Clostridium increased with pit mud quality, further influencing the quality of baijiu.

Occurrence, Diversity, and Character of Bacillaceae in the Solid Fermentation Process of Strong Aromatic Liquors

Strong aromatic liquors, also known as strong aromatic Baijiu (SAB) in China, are manufactured by solid fermentation, with a multi-microbe mixing and cooperative fermentation process that uses Daqu as a brewing starter. Bacillaceae have a specific action in food fermentation, such as soybean and wine, and more recent studies have found Bacillaceae play important roles in the SAB making industry. This review describes the diversity, functionality, and influence of Bacillaceae in Daqu, pit mud, Zaopei, Huangshui within making processes of SAB. Furthermore, aromatic flavor components from the Bacillaceae metabolism of SAB are discussed in this review. Ultimately, the resulting improvements and deeper understanding will benefit practical efforts to apply representatives of Bacillaceae in improving the quality of SAB as well as biological control of the micro-ecological environment of brewing.

16S rRNA genes- and metagenome-based confirmation of syntrophic butyrate-oxidizing methanogenesis enriched in high butyrate loading

The understanding and enrichment of consortia formed by syntrophic butyrate-oxidizing bacteria and methanogens in the complex environment are crucial for effectively degrading butyrate and preventing acid inhibition. In this study, the better butyrate-tolerated and highly efficient microbial consortia were domesticated and enriched through adding butyric acid ranging from 0.2 to 4.4 g/(L·d). The volumetric biogas production continuously increased to 1.65 L/(L·d). Microbial community diversity showed that a dramatic shift of bacterial structure occurred at BAL of 1.6 g/(L·d) and the structure presented better stability at high BAL. The syntrophic consortia and the main metabolic pathways were revealed through combination of the 16S rDNA and metagenome sequencing analyses. Syntrophomonas was the major butyrate-oxidizing bacterium and oxidized butyrate mainly through β-oxidaiton. Synergistaceae and Mesotoga acted as the main acetate-oxidizing bacteria. IHT and methanogenesis pathways were strongly enhanced by DMER64 and Methanosarcina as the main H₂ carrier and dominant methanogen, respectively.

Flavor mystery of Chinese traditional fermented baijiu: The great contribution of ester compounds

Chinese traditional fermented baijiu is a famous alcoholic beverage with unique flavor. Despite its consumption for millennia, the flavor mystery behind baijiu is still unclear. Studies indicate that esters are the most important flavor substances, and bring health benefits. However, the aroma contribution and formation mechanism of esters still need to be clarified to reveal the flavor profile of baijiu. This review systematically summarizes all the 510 esters and finds 9 ethyl esters contribute greatly to the flavor of baijiu. The 508 different microbial species that have been identified affect the synthesis of esters through fatty acid and amino acid metabolism. The determination of minimum functional microbial groups and the analysis of their metabolic characteristics are crucial to reveal the mechanism of formation of baijiu flavor, and ensure the reproducible formation of flavor substances.

Comparative genome analysis of Clostridium beijerinckii strains isolated from pit mud of Chinese strong flavor baijiu ecosystem

Clostridium beijerinckii is a well-known anaerobic solventogenic bacterium which inhabits a wide range of different niches. Previously, we isolated five butyrate-producing C. beijerinckii strains from pit mud (PM) of strong-flavor baijiu (SFB) ecosystems. Genome annotation of the five strains showed that they could assimilate various carbon sources as well as ammonium to produce acetate, butyrate, lactate, hydrogen, and esters but did not produce the undesirable flavors isopropanol and acetone, making them useful for further exploration in SFB production. Our analysis of the genomes of an additional 233 C. beijerinckii strains revealed an open pangenome based on current sampling and will likely change with additional genomes. The core genome, accessory genome, and strain-specific genes comprised 1567, 8851, and 2154 genes, respectively. A total of 298 genes were found only in the five C. beijerinckii strains from PM, among which only 77 genes were assigned to Clusters of Orthologous Genes categories. In addition, 15 transposase and 12 phage integrase families were found in all five C. beijerinckii strains from PM. Between 18 and 21 genome islands were predicted for the five C. beijerinckii genomes. The existence of a large number of mobile genetic elements indicated that the genomes of the five C. beijerinckii strains evolved with the loss or insertion of DNA fragments in the PM of SFB ecosystems. This study presents a genomic framework of C. beijerinckii strains from PM that could be used for genetic diversification studies and further exploration of these strains.

The prokaryotic community, physicochemical properties and flavors dynamics and their correlations in fermented grains for Chinese strong-flavor Baijiu production

Fermented grain (FG), a complex and unique ecosystem, is the main microbial habitats, biochemical reaction system and direct source of flavor compounds for the Chinese strong-flavor Baijiu (CSFB) production. However, the dynamics of physicochemical properties, prokaryotic community and flavor compounds of FGs during the long-term fermentation process are still not completely clear. Here, the above topics on FGs in the actual production process were comprehensively studied by using a combination of physicochemical analysis, GC-MS detection and Illumina HiSeq sequencing methods. The whole fermentation process could be divided into two stages including early (0-25d) and the later stage (25-60d) based on the dynamics of FG physicochemical properties and the changes of prokaryotic community diversity. A total of 41phyla and 364 genera were detected, and 9 of them were dominant genera in FG complex ecosystem, including Lactobacillus, Pediococcus, Ochrobactrum, Bacillus etc. Among them, the dynamics of 29 top10 genera in FGs were mainly influenced by the starch and total acid, followed by NH₄⁺ and ethanol, and 7 genera (hubs, e.g., Clostridium, Methanosaeta, Bacillus, etc.) of them may play important roles in FG ecosystem stability. A total of 71 volatiles including 33 esters, 14 alcohols, 9 fatty acids, 5 phenols, and 10 other compounds were detected in the FGs, and most of them formed in the early stage. Some important flavor substances (e.g., ethyl octanoate, 3-methylbutanol, hexanoate, etc.) increased in the later stage. Moreover, the formation of some flavor compound might require multiple microbes involved. For instance, ten of the top10 genera, including Lactobacillus, Clostridium, Methanosarcina, Sedimentibacter, Bacillus, etc., were significantly and positively correlated with four important esters. This study may help to clarify the complex correlations among prokaryotic community, physicochemical properties and flavors, allow the improvement of CSFB quality by using bioaugmentation and/or controlling environmental factors, and shed more light on the ecological rules guiding community assembly in FGs.

Novisyntrophococcus fermenticellae gen. nov., sp. nov., isolated from an anaerobic fermentation cellar of Chinese strong-flavour baijiu

A Gram-stain-negative, coccus-shaped, obligately anaerobic, non-motile and non-spore-forming bacterium, designated strain JN500902^T, was isolated from the mud in a fermentation cellar used continuously over 30 years for Chinese strong-flavour baijiu production. Colonies were white, circular, convex and smooth-edged. Growth was observed at 20-40 °C (optimum, 37 °C), at pH 5.0-10 (optimum, pH 7.5), with 0-2 % (w/v) NaCl and with 0-4 % (v/v) ethanol. The Biolog assay demonstrated positive reactions of strain JN500902^T in the metabolism of l-fucose and pyruvate. The predominant cellular fatty acids (>10 %) consisted of C_16 : 0 and C_14 : 0. The major end metabolites of strain JN500902^T were acetic acid and ethanol when incubated anaerobically in liquid reinforced clostridial medium. Acetate was the major organic acid end product. The complete genome size of strain JN500902^T was 3 420 321 bp with 3327 identified genes. The G+C content was 43.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences affiliated strain JN500902^T with the family Lachnospiraceae, having low sequence similarity (92.8 %) to the nearest type strain, Syntrophococcus sucromutans DSM 3224^T and forming a clearly distinct branch. Core genome phylogenetic analysis of the isolate and 134 strains belonging to the family Lachnospiraceae also revealed that strain JN500902^T was well-separated from other genera of this family as a monophyletic clade. The average nucleotide identity and amino acid identity values between strain JN500902^T and 134 Lachnospiraceae strains were less than 74 and 65 %, respectively. Considering its polyphasic characteristics, strain JN500902^T represents a novel genus and species within the family Lachnospiraceae, for which the name Novisyntrophococcus fermenticellae gen. nov., sp. nov. is proposed. The type strain is JN500902^T (=CICC 24502^T=JCM 33939^T).

Production of medium-chain fatty acid caproate from Chinese liquor distillers' grain using pit mud as the fermentation microbes

Chinese liquor distillers' grain (CLDG) is an abundant industrial organic waste showing high potential as feedstock for biofuel conversion. In this study, CLDG was used as substrate by microbial community in pit mud to produce medium-chain fatty acids (especially caproate). Simulated and real fermentation were used to evaluate the effect of ethanol and lactic acid being the electronic donors (EDs) during the anaerobic chain elongation (CE). The caproate concentration was achieved at 449 mg COD/g VS, with the corresponding high carbon selectivity at 37.1%. Microbial analysis revealed that the domestication of pit mud increased the abundance of Caproiciproducens (converting lactic acid into caproate) and Lactobacillus (producing lactic acid), leading to enhanced caproate production. The lactic acid conversion facilitated in full utilization of ethanol through CE consumption. The coexistence of EDs benefited the CE system and that this green energy production can be a promising high-performance biofuel donor for sustainable industrial production development.

Mining the Factors Driving the Evolution of the Pit Mud Microbiome under the Impact of Long-Term Production of Strong-Flavor Baijiu

The mud cellar creates a unique microenvironment for the fermentation of strong-flavor baijiu (SFB). Recent research and long-term practice have highlighted the key roles of microbes inhabiting pit mud in the formation of SFB’s characteristic flavor. A positive correlation between the quality of SFB and cellar age was extracted from practice; however, the evolutionary patterns of pit mud microbiome and driving factors remain unclear. Here, based on the variation regularity analysis of microbial community structure and metabolites of samples from cellars of different ages (∼30/100/300 years), we further investigated the effects of lactate and acetate (main microbial metabolites in fermented grains) on modulating the pit mud microbiome. Esters (50.3% to 64.5%) dominated the volatile compounds identified in pit mud, and contents of the four typical acids (lactate, hexanoate, acetate, and butyrate) increased with cellar age. Bacteria (9.5 to 10.4 log₁₀ [lg] copies/g) and archaea (8.3 to 9.1 lg copies/g) mainly constituted pit mud microbiota, respectively dominated by Clostridia (39.7% to 81.2%) and Methanomicrobia (32.8% to 92.9%). An upward trend with cellar age characterized the relative and absolute abundance of the most predominant bacterial and archaeal genera, Caproiciproducens and Methanosarcina. Correlation analysis revealed significantly (P < 0.05) positive relationships between the two genera and major metabolites. Anaerobic fermentation with acetate and lactate as carbon sources enhanced the enrichment of Clostridia, and furthermore, the relative abundance of Caproiciproducens (40.9%) significantly increased after 15-day fed-batch fermentation with lactate compared with the initial pit mud (0.22%). This work presents a directional evolutionary pattern of pit mud microbial consortia and provides an alternative way to accelerate the enrichment of functional microbes.

IMPORTANCE The solid-state anaerobic fermentation in a mud cellar is the most typical feature of strong-flavor baijiu (SFB). Metabolites produced by microbes inhabiting pit mud are crucial to create the unique flavor of SFB. Accordingly, craftspeople have always highlighted the importance of the pit mud microbiome and concluded by centuries of practice that the production rate of high-quality baijiu increases with cellar age. To deepen the understanding of the pit mud microbiome, we determined the microbial community and metabolites of different-aged pit mud, inferred the main functional groups, and explored the forces driving the microbial community evolution through metagenomic, metabolomic, and multivariate statistical analyses. The results showed that the microbial consortia of pit mud presented a regular and directional evolutionary pattern under the impact of continuous batch-to-batch brewing activities. This work provides insight into the key roles of the pit mud microbiome in SFB production and supports the production optimization of high-quality pit mud.

MXene-coated biochar as potential biocathode for improved microbial electrosynthesis system

Microbial electrosynthesis (MES) holds tremendous large scale energy storage potential. By promoting the bioconversion of carbon dioxide (bicarbonate) into useful chemical commodities, this technique utilizes renewable energy and reduces carbon footprint. However, expensive electrode materials, low current densities, and multiple electrosynthesis products are major challenges to this field. To this end, this study examines a multilayered and conductive MXene structure that was coated on a cost-effective biochar substrate and tested as a MES cathode. These results show this coating yielded improved electrical conductivity, increased charge transfer efficiency, and selective microbial enrichment characteristics, resulting in a 2.3-fold increase in cathodic current production in comparison to the uncoated biochar. Moreover, an increase in active sites improved mass transfer and microbial growth, producing 1.7-fold increase in butyrate in comparison to the uncoated control. Considering that electrode attached microbial communities play a major role in final products, microbial community analyses was completed, suggesting that selective microbial enrichment was promoted as Firmicutes (66%), Proteobacteria (13%), and Bacteroidetes (12%) (i.e., exoelectrogenic and butyrate producing phyla) which were dominant in the MXene-coated biochar biofilm. These results show that biochar modification is an effective technique for achieving selective products through MES.

Cooperation within the microbial consortia of fermented grains and pit mud drives organic acid synthesis in strong-flavor Baijiu production

Mud cellars have long been used as anaerobic bioreactors for the fermentation of Chinese strong-flavor Baijiu, where starchy raw materials (mainly sorghum) are metabolized to ethanol and various flavor compounds by multi-species microorganisms. Jiupei (fermented grains) and pit mud are two spatially linked microbial habitats in the mud cellar, yet their metabolic division of labor remains unclear. Here, we investigated the changes in environmental variables (e.g., temperature, oxygen, pH), key metabolites (e.g., ethanol, organic acids) and microbial communities in jiupei and pit mud during fermentation. Jiupei (low pH, high ethanol) and pit mud (neutral pH) provided two habitats with distinctly different environmental conditions for microbial growth. Lactic acid accumulated in jiupei, while butyric and hexanoic acids were mainly produced by microbes inhabiting the pit mud. Biomass analysis using quantitative real-time PCR showed that bacteria dominated the microbial consortia during fermentation, moreover cluster and principal coordinate analysis (PCoA) analysis showed that the bacterial communities of jiupei and pit mud were significantly divergent. The bacterial community diversity of jiupei decreased significantly during the fermentation process, and was relatively stable in pit mud. Lactobacillus dominated the jiupei bacterial community, and its relative abundance reached 98.0% at the end of fermentation. Clostridia (relative abundance: 42.9-85.5%) was the most abundant bacteria in pit mud, mainly distributed in the genus Hydrogenispora (5.3-68.4%). Fungal communities of jiupei and pit mud showed a similar succession pattern, and Kazachstania, Aspergillus and Thermoascus were the predominant genera. PICRUSt analysis demonstrated that enzymes participating in the biosynthesis of acetic and lactic acid were mainly enriched in jiupei samples, while the bacterial community in the pit mud displayed greater potential for butyric and hexanoic acid synthesis. Assays from an in vitro simulated fermentation further validated the roles of jiupei microbiota in acetic and lactic acid production, and these acids were subsequently metabolized to butyric and hexanoic acid by the pit mud microbiota. This work has demonstrated the synergistic cooperation between the microbial communities of jiupei and pit mud for the representative flavor formation of strong-flavor Baijiu.

Gut Microbiota-Derived Short-Chain Fatty Acids Promote Prostate Cancer Growth via IGF1 Signaling

Excessive intake of animal fat and resultant obesity are major risk factors for prostate cancer. Because the composition of the gut microbiota is known to change with dietary composition and body type, we used prostate-specific Pten knockout mice as a prostate cancer model to investigate whether there is a gut microbiota-mediated connection between animal fat intake and prostate cancer. Oral administration of an antibiotic mixture (Abx) in prostate cancer-bearing mice fed a high-fat diet containing a large proportion of lard drastically altered the composition of the gut microbiota including Rikenellaceae and Clostridiales, inhibited prostate cancer cell proliferation, and reduced prostate Igf1 expression and circulating insulin-like growth factor-1 (IGF1) levels. In prostate cancer tissue, MAPK and PI3K activities, both downstream of the IGF1 receptor, were suppressed by Abx administration. IGF1 directly promoted the proliferation of prostate cancer cell lines DU145 and 22Rv1 in vitro. Abx administration also reduced fecal levels of short-chain fatty acids (SCFA) produced by intestinal bacteria. Supplementation with SCFAs promoted tumor growth by increasing IGF1 levels. In humans, IGF1 was found to be highly expressed in prostate cancer tissue from obese patients. In conclusion, IGF1 production stimulated by SCFAs from gut microbes influences the growth of prostate cancer via activating local prostate MAPK and PI3K signaling, indicating the existence of a gut microbiota-IGF1-prostate axis. Disrupting this axis by modulating the gut microbiota may aid in prostate cancer prevention and treatment. SIGNIFICANCE: These results suggest that intestinal bacteria, acting through short-chain fatty acids, regulate systemic and local prostate IGF1 in the host, which can promote proliferation of prostate cancer cells.

Caproicibacterium amylolyticum gen. nov., sp. nov., a novel member of the family Oscillospiraceae isolated from pit clay used for making Chinese strong aroma-type liquor

An anaerobic, Gram-stain-positive, rod-shaped, motile and spore-forming bacterium, designated strain LBM18003^T, was isolated from pit clay used for making Chinese strong aroma-type liquor. Growth occurred at 20-40 °C (optimum, 30-37 °C), pH 4.5-9.5 (optimum, pH 6.5-7.0) and in the presence of 0.0-1.0 % (w/v) sodium chloride (optimum, 0 %). The predominant fatty acids were C_16:0, C_14:0, C_14:0 DMA and C_16:0 3-OH, and the major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, two unidentified phospholipids and nine unidentified glycolipids. Phylogenetic analysis revealed that strain LBM18003^T is a novel member of the family Oscillospiraceae. The 16S rRNA gene sequence similarities of strain LBM18003^T to its two most closely related species were less than 94.5 % for distinguishing genera, i.e. closely related to Caproiciproducens galactitolivorans JCM 30532^T (94.1 %) and Caproicibacter fermentans DSM 107079^T (93.2 %). The genome size of strain LBM18003^T was 2 996 201 bp and its DNA G+C content was 48.48 mol%. Strain LBM18003^T exhibited 67.8 and 68.1% pairwise-determined whole-genome average nucleotide identity values to Caproiciproducens galactitolivorans JCM 30532^T and Caproicibacter fermentans DSM 107079^T, respectively; and showed 62.2 and 61.0 % the average amino acid identity values to Caproiciproducens galactitolivorans JCM 30532^T and Caproicibacter fermentans DSM 107079^T, respectively; and demonstrated 46.1 and 41.5 % conserved genes to Caproiciproducens galactitolivorans JCM 30532^T and Caproicibacter fermentans DSM 107079^T, respectively. The comparisons of 16S rRNA gene and genome sequences confirmed that strain LBM18003^T represented a novel genus of the family Oscillospiraceae. Based on morphological, physiological, biochemical, chemotaxonomic, genotypic and phylogenetic results, strain LBM18003^T represents a novel species of a novel genus of the family Oscillospiraceae, for which the name Caproicibacterium amylolyticum gen. nov., sp. nov. is proposed. The type strain is LBM18003^T (=GDMCC 1.1626^T=JCM 33783^T).

The effects of dynamic bacterial succession on the flavor metabolites during Baijiu fermentation

The succession of microbial community significantly affect the flavor formation of traditional fermented foods and beverages. Chinese liquor (Baijiu) fermentation is a typical spontaneous solid-state fermentation process driven by natural microbiota. The type of process used to make liquor-craft or industrial-alters the operational environment and the aromatic qualities of the product contributed by various microbial consortia. But differences in microbial community assembly and temporal succession are often overlooked. In this study, we investigated bacterial community dynamics, substrate consumption, and metabolite production during both craft and industrial liquor-making processes (CLP and ILP, respectively). We found that the compositions of bacterial communities were different, even though no significant difference (p > 0.05) was observed in bacterial species between CLP and ILP at the beginning of fermentation. During ILP, glucose was used more rapidly by microflora, leading in turn to a higher ethanol production rate during the early stage of fermentation. The higher rate of ethanol production in ILP shortened the lifetime of bacteria such as Weissella, Pediococcus, Leuconostoc, and Bacillus during the early stage of fermentation. Lactobacillus sp. became dominant earlier in ILP than in CLP. Finally, the change in bacterial community dynamics led to changes in aroma compounds. Using CLP and ILP as a model system, our results illustrate the dynamic nature of Baijiu fermentations and microbial succession patterns therein. This can be applied to optimize the fermentation processes and flavors attributes of this and other fermented foods.

Daqu microbiota exhibits species-specific and periodic succession features in Chinese baijiu fermentation process

Daqu, a brick-shaped product spontaneously fermented under an open environment, has been regarded as the starter of fermentation, raw enzyme preparation and raw materials for baijiu production. However, its contribution in baijiu fermentation has not been fully elaborated yet. Here, the effects of daqu microbiota on baijiu fermentation were investigated under both field-scale and lab-scale conditions. In field-scale baijiu fermentation, the dominant daqu microbes (average relative abundance>10.0%), including unclassified_Leuconostocaceae, Thermoascus, and Thermomyces, tended to dominate the early stage (0-7 d). However, the rare daqu microbes (average relative abundance <0.1%, e.g., Kazachstania) tended to dominate the middle and late stages (11-40 d). In addition, some genera showed differences in species diversity between daqu and fermented grains. The average relative abundance of Lactobacillus was over 75% during baijiu fermentation, and most of them were affiliated with Lactobacillus acetotolerans, while Lactobacillus crustorum dominated the Lactobacillus OTUs in daqu. The similar patterns were also observed during lab-scale baijiu fermentation. The results of function prediction showed the enriched metabolic pathways were associated with glycolysis and long-chain fatty acid esters in baijiu fermentation. These results improved the understanding of daqu microbiota function during baijiu fermentation and provided a basic theory to support the regulation of baijiu production.

Characterization of Microbial Diversity and Community Structure in Fermentation Pit Mud of Different Ages for Production of Strong-Aroma Baijiu

In the traditional fermentation process of strong-aroma Baijiu, a fermentation pit mud (FPM) provides many genera of microorganisms for fermentation. However, the functional microorganisms that have an important effect on the quality of Baijiu and their changes with the age of fermentation pit (FP) are poorly understood. Herein, the Roche 454 pyrosequencing technique and a phospholipid fatty-acid analysis were employed to reveal the structure and diversity of prokaryotic communities in FPM samples that have been aged for 5, 30, and 100 years. The results revealed an increase in total prokaryotic biomass with an FP age; however, Shannon’s diversity index decreased significantly (p < 0.01). These results suggested that a unique microbial community structure evolved with uninterrupted use of the FP. The number of functional microorganisms, which could produce the flavor compounds of strong-aroma Baijiu, increased with the FP age. Among them, Clostridium and Ruminococcaceae are microorganisms that directly produce caproic acid. The increase of their relative abundance in the FPM might have improved the quality of strong-aroma Baijiu. Syntrophomonas, Methanobacterium, and Methanocorpusculum might also be beneficial to caproic acid production. They are not directly involved but provide possible environmental factors for caproic acid production. Overall, our study results indicated that an uninterrupted use of the FP shapes the particular microbial community structure in the FPM. This research provides scientific support for the concept that the aged FP yields a high-quality Baijiu.