Illuminating Anaerobic Microbial Community and Cooccurrence Patterns across a Quality Gradient in Chinese Liquor Fermentation Pit Muds

Caproiciproducens converts lactic acid into caproic acid during Chinese strong-flavor Baijiu brewing

Strong-flavor Baijiu, a type of Chinese liquor, is produced through anaerobic solid-state fermentation in a sealed mud pit. Ethyl caproate, the characteristic flavor compound of strong-flavor Baijiu, is influenced by caproic acid-producing bacteria in the pit mud. To better understand the formation of caproic acid, this study investigated the microbial composition and physicochemical parameters of pit mud from different layers (top, middle, and bottom) in Hubei and Sichuan provinces, China. The results revealed that Caproiciproducens plays a key role in caproic acid production by using lactic acid as a substrate, with its abundance increasing with the depth of the pit mud. A strain Caproiciproducens sp. R1, isolated from the pit mud, was shown to produce caproic acid from lactic acid within an initial pH range of 5.5-9.0 and lactic acid concentrations of 1 %-5 % (m/v). In addition, inoculation of strain R1 into Huangshui (a lactic acid-rich liquid from Baijiu production) resulted in 40.72 mM caproic acid production. This study demonstrates that Caproiciproducens plays a crucial role in caproic acid production from lactic acid during the fermentation process of strong-flavor Baijiu.

Microbial succession in different years of pit mud from a distillery in Sichuan for Nong-xiang Baijiu fermentation

Microbial community and succession of 5-, 20-, and 50-year pit mud (PM) were uncovered in this study. The results showed that Bacteroidetes, Firmicutes and Ascomycota were dominant phyla in these PM samples. Interestingly, most sequences could not be classified into fungal taxa at the genus level by UNITE Database, the diversity and richness of bacteria in these PMs were higher than that of fungi. It was noteworthy that both 20-year and 50-year PMs exhibited higher abundances of Caproiciproducens and Petrimonas when compared with 5-year PM. While higher proportions of Lactobacillus and Acinetobacter were observed in the 5-year PM. Furfermore, these PMs microbiota mainly involved biosynthesis, degradation, and generation of precursor metabolites, which contributed to carbon cycling of Nong-xiang Baijiu anaerobic fermentation. Taken together, lactic acid bacteria depletion and caproic acid bacteria accumulation might be an important succession trend of PM microbiota during the long-term fermentation of Chinese Nong-xiang Baijiu.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-024-01558-4.

Heterogenetic mechanism in multidimensional pit mud with different fermentation years: From microbial structure dynamic succession to metabolism phenotypes

Pit mud (PM) is fermenting agents in the strong-flavor baijiu (SFB) production. In this paper, the discrepancies in fermentation parameters, microbial community succession patterns and metabolic phenotypes were compared in multidimensional PMs. The results showed that pyruvic acid, succinic acid, S-Acetyldihydrolipoamide-E, glycerol and glyceric acid were the key metabolites responsible for the metabolic differences between the 2-, 30-,100- and 300-year multidimensional PMs, while the butanoic acid, heptyl, heptanoic acid, heptanoic acid ethyl ester, hexanoic acid and octanoic acid were the key differential flavor compounds in the 2-, 30-,100- and 300-year multidimensional PMs. Concurrently, the diversity and abundance of microbial community also exhibited significant differences between the new and old multidimensional PMs, the assembly pattern of bacterial communities changed from deterministic to stochasticity from lower (bottom of the pit and under the huangshui fluid) to upper PM (up the huangshui fluid and top of the pit). Key microorganisms related to the succession process of the lower PM were Clostridium, Methanobacterium, Petrimonas, Lactobacillus, Methanobrevibacter, Bellilinea, Longilinea, Bacillus. In contrast, the upper PM were Caproicibacter, Longilinea, Lactobacillus, Proteinphilum, Methanobrevibacter, Methanobacterium, Methanobacteriaceae, Petrimonas, Bellilinea and Atopobium. Redundancy analysis (RDA) indicated that the key environmental factors regulating the succession of microbial in upper PM were lactic acid, moisture, pH and available phosphorus. In contrast, the lower was lactic acid, acetic acid and ammonia N. Based on these results, heterogeneous mechanisms between new and old multidimensional PMs were explored, providing a theoretical support for improving the quality of new PM.

Effects of community ecological network construction on physicochemical, microbial, and quality characteristics of inoculated northeast sauerkraut: A new insight in food fermentation processes

The enhancement of the quality of northeast sauerkraut can be achieved by inoculation with lactic acid bacteria. However, a comprehensive ecological understanding of the intricate dynamic processes involved is currently lacking, which could yield valuable insights for regulating sauerkraut fermentation. This study compares spontaneously sauerkrauts with the sauerkrauts inoculated with autochthonous Lactiplantibacillus plantarum SC-MDJ and commercial L. plantarum, respectively. We examine their physicochemical properties, quality characteristics, bacterial community dynamics, and ecological network interactions. Inoculation with L. plantarum leads to reduced bacterial community richness and niche breadth, but an increase in robustness, interactions, and assembly processes. Notably, there appears to be a potential correlation between bacterial community structure and quality characteristics. Particularly, sauerkraut inoculated with L. plantarum SC-MDJ may produce a sourness more quickly, possibly attributed to the enhanced ecological role of L. plantarum SC-MDJ. This study establishes a foundation for the targeted regulation of sauerkraut fermentation.

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.

Workshop environment heterogeneity shaped the microbiome and metabolome profiles during Xiasha round of Jiangxiangxing Baijiu

Workshop with different fermentation years plays an essential role in the yield and quality of Baijiu. In actual production, the quality of base Baijiu in newly built workshop is inferior to the older one. In this study, the microbiota of workshop environment and fermentation process from two workshops namely N (ferment 2 years) and O (ferment 20 years) and flavor compounds were studied during Xiasha round. Results showed workshop O accumulated more environmental microorganisms and fungi including P. kudriavzevii, Wickerhamomyces anomalus and Saccharomyces sp mainly came from ground. Yeasts including Pichia, Cyberlindnera, Wickerhamomyces and Candida were responsible for flavor substances formation in O while Saccharopolyspora was in N. This study for the first time explored the reasons for the brewing differences among N and O workshop from perspectives of workshop environment, microbial community and flavor substances, providing new ideas for guiding production as well as improvement of Baijiu quality.

Caproicibacter sp. BJN0012, a potential new species isolated from cellar mud for caproic acid production from glucose

Acids play a crucial role in enhancing the flavor of strong-aroma Baijiu, and among them, caproic acid holds significant importance in determining the flavor of the final product. However, the metabolic synthesis of caproic acid during the production process of Baijiu has received limited attention, resulting in fluctuations in caproic acid content among fermentation batches and generating production instability. Acid-producing bacteria found in the cellar mud are the primary microorganisms responsible for caproic acid synthesis, but there is a lack of research on the related microbial resources and their metabolic properties. Therefore, it is essential to identify and investigate these acid-producing microorganisms from cellar mud to ensure stable caproic acid synthesis. In this study, a unique strain was isolated from the cellar mud, exhibiting a 98.12 % similarity in its 16 S rRNA sequence and an average nucleotide identity of 79.57 % with the reference specie, together with the DNA-DNA hybridization of 23.20 % similarity, confirming the distinct species boundaries. The strain was able to produce 1.22 ± 0.55 g/L caproic acid from glucose. Through genome sequencing, annotation, and bioinformatics analysis, the complete pathway of caproic acid synthesis from glucose was elucidated, and the catalytic mechanism of the key thiolase for caproic acid synthesis was investigated. These findings provide useful fundamental data for revealing the metabolic properties of caproic acid-producing bacteria found in cellar mud.

Analysis of differences in microorganisms and aroma profiles between normal and off-flavor pit mud in Chinese strong-flavor Baijiu

The unique cellar fermentation process of Chinese strong-flavor Baijiu is the reason for its characteristic cellar aroma flavor. The types, abundance, community structure and metabolic activity of microorganisms in the pit mud directly affect the microbial balance in the white spirit production environment, promoting the formation of typical aromas and influencing the quality of CFSB. During the production process, the production of off-flavor in the cellar may occur. The aim of this study is to elucidate the differences in microbiota and flavor between normal pit mud and abnormal pit mud (pit mud with off-flavor). A total of 46 major volatile compounds were identified, and 24 bacterial genera and 21 fungal genera were screened. The esters, acids, and alcohols in the abnormal pit mud were lower than those in the normal pit mud, while the aldehydes were higher. 3-Methyl indole, which has been proven to be responsible for the muddy and musty flavors, was detected in both types of pit mud, and for the first time, high levels of 4-methylanisole was detected in the pit mud. The microbial composition of the two types of pit mud showed significant differences in the bacterial genera of Sporosarcina, Lactobacillus, Garciella, Anaerosalibacter, Lentimicrobium, HN-HF0106, Petrimonas, Clostridium_sensu_stricto_12 and Bacillus, and the fungal genera of Millerozyma, Penicillium, Mortierella, Monascus, Saccharomyces, Issatchenkia, Pithoascus, Pseudallescheria, and Wickerhamomyces. Additionally, we speculate that Sporosarcina is the predominant bacterial genus responsible for the imbalance of microbiota in pit mud.

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.

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.

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.

Genome Analysis and Optimization of Caproic Acid Production of Clostridium butyricum GD1-1 Isolated from the Pit Mud of Nongxiangxing Baijiu

Caproic acid is a precursor substance for the synthesis of ethyl caproate, the main flavor substance of nongxiangxing baijiu liquor. In this study, Clostridium butyricum GD1-1, a strain with high caproic acid concentration (3.86 g/l), was isolated from the storage pit mud of nongxiangxing baijiu for sequencing and analysis. The strain's genome was 3,840,048 bp in length with 4,050 open reading frames. In addition, virulence factor annotation analysis showed C. butyricum GD1-1 to be safe at the genetic level. However, the annotation results using the Kyoto Encyclopedia of Genes and Genomes Automatic Annotation Server predicted a deficiency in the strain's synthesis of alanine, methionine, and biotin. These results were confirmed by essential nutrient factor validation experiments. Furthermore, the optimized medium conditions for caproic acid concentration by strain GD1-1 were (g/l): glucose 30, NaCl 5, yeast extract 10, peptone 10, beef paste 10, sodium acetate 11, L-cysteine 0.6, biotin 0.004, starch 2, and 2.0% ethanol. The optimized fermentation conditions for caproic acid production by C. butyricum GD1-1 on a single-factor basis were: 5% inoculum volume, 35°C, pH 7, and 90% loading volume. Under optimal conditions, the caproic acid concentration of strain GD1-1 reached 5.42 g/l, which was 1.40 times higher than the initial concentration. C. butyricum GD1-1 could be further used in caproic acid production, NXXB pit mud strengthening and maintenance, and artificial pit mud preparation.

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.

Microbial communities and their correlation with flavor compound formation during the mechanized production of light-flavor Baijiu

Light-flavor Baijiu fermentation is a typical spontaneous solid-state fermentation process fueled by a variety of microorganisms. Mechanized processes have been increasingly employed in Baijiu production to replace traditional manual operation processes, however, the microbiological and physicochemical dynamics in mechanized processes remain largely unknown. Here, we investigated the microbial community succession and flavor compound formation during a whole mechanized fermentation process of light-flavor Baijiu using the conventional dilution plating method, PacBio single-molecule real-time (SMRT) sequencing and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry. The results showed that largely different fungal and bacterial communities were involved in the soaking and fermentation processes. A clear succession from Pantoea agglomerans to Bacillus (B.) smithii and B. coagulans in dominant bacterial species and from Cladosporium exasperatum to Saccharomyces cerevisiae and Lichtheimia ramosa in dominant fungal species occurred in the soaking processes. In the fermentation process, the most dominant bacterial species was shifted from Pantoea agglomerans to Lactobacillus (La.) acetotolerans and the most dominant fungal species were shifted from Lichtheimia ramose and Rhizopus arrhizus to Saccharomyces cerevisiae. The bacterial and fungal species positively associated with acidity and the formation of ethanol and different flavor compounds were specified. The microbial species exhibited strong co-occurrence or co-exclusion relationships were also identified. The results are helpful for the improvement of mechanized fermentation process of light-flavor Baijiu production.

Potential Correlation between Microbial Diversity and Volatile Flavor Substances in a Novel Chinese-Style Sausage during Storage

A novel Chinese-style sausage with Chinese traditional fermented condiments used as additional ingredients is produced in this study. The aim of this study was to investigate the microbial community's structure, the volatile flavor substances and their potential correlation in the novel Chinese sausage. High-throughput sequencing (HTS) and solid-phase microextraction-gas chromatography-mass spectrometry (GC-MS) were, respectively, used to analyze the microbial diversity and volatile flavor substances of the novel Chinese-style sausage during storage. The results showed that Firmicutes, Proteobacteria and Actinobacteria were the predominant bacterial genera, and Hyphopichia and Candida were the predominant fungal genera. A total of 88 volatile flavor substances were identified through GC-MS, among which 18 differential flavor compounds were screened (VIP > 1), which could be used as potential biomarkers to distinguish the novel sausages stored for different periods. Lactobacillus exhibited a significant negative correlation with 2,3-epoxy-4,4-dimethylpentane and acetoin and a significant positive correlation with 2-phenyl-2-butenal. Hyphopichia significantly positively correlated with ester. Leuconostoc significantly positively correlated with ethyl caprate, ethyl palmate, ethyl tetradecanoate and ethyl oleate while it negatively correlated with hexanal. This study provides a theoretical basis for revealing the flavor formation mechanisms and the screening of functional strains for improving the flavor quality of the novel Chinese-style sausage.

Application of Clostridium butyricum, Rummeliibacillus suwonensis, and Issatchenkia orientalis for Nongxiangxing baijiu fermentation: Improves the microbial communities and flavor of upper fermented grain

Ethyl hexanoate and ethyl butyrate are essential to the flavor compounds in Nongxiangxing baijiu, but low levels of these two esters in upper fermented grains (FG) decreases the quality of upper distilled baijiu, representing the main challenge in Nongxiangxing baijiu production. This paper enhanced fermentation by inoculating functional Clostridium butyricum, Rummeliibacillus suwonensis, and Issatchenkia orientalis strains into upper FG. The results showed that the ethyl butyrate content in the upper FG increased significantly and the content of ethyl hexanoate did improve from the results of many determinations. High-throughput sequencing indicated that the dominant phyla in the FG were Firmicutes, Actinobacteriota, Proteobacteria, Ascomycota, and Basidiomycota. The canonical correspondence analysis (CCA) and person correlation network revealed the relationship between the microbial community, physicochemical environment, and flavor compounds. The temperature, oxygen, and acidity were closely related to the microbial community, while most flavor compounds were positively correlated with Caldicoprobacter, Caproiciproducens, Delftia, Hydrogenispora, Thermoactinomyces, Issatchenkia Bacillus, and Aspergillus. These results helped improve the quality of Nongxiangxing baijiu.

Clostridium aromativorans sp. nov., isolated from pit mud used for producing Wuliangye baijiu

A strictly anaerobic, gram-positive bacterium, designated as WLY-B-L2^T, was isolated from pit mud of a fermentation pit located at Wuliangye 501# baijiu workshop in Yibin (Sichuan province, PR China). The strain was strictly anaerobic, Gram-positive with straight or somewhat rod shaped cells which were 0.5-0.7 μm wide and 1.7-3.1 μm long, arranged singly or in pairs. The strain can utilize D-galacturonic acid, methyl pyruvate, L-lactamine, L-alanyl - L-glutamine, L-alanyl - L-histidine, glycerol, pyruvate, L-alanyl - L-threonine, L-methionine, L-phenylalanine, L-valine + L-aspartic acid, L-serine, L-valine, and thymidine as carbon sources. Major cellular fatty acids are C_{16: 0} (24.6%), anteiso-C_{15: 0} (16.5%), and iso-C_{15: 0} (14.1%). Based on 16S rRNA gene sequence, WLY-B-L2^T is most closely related to Clostridium luticellarii FW431^T; they exhibit 97.42% 16S rRNA similarity. Additionally, the digital DNA-DNA hybridization (dDDH) value between them is 28.10%. WLY-B-L2^T has a G + C content of 34.16 mol%. Based on the evidence presented here, WLY-B-L2^T (CICC 25133^T = JCM 35127^T) is proposed as the type strain of a novel species, designated as Clostridium aromativorans sp. nov, that could produce butyric acid and volatile flavor components, such as ethyl valerate, ethyl acetate and 2-pentanone.

Effect of Multiple Rounds of Enrichment on Metabolite Accumulation and Microbiota Composition of Pit Mud for Baijiu Fermentation

Pit mud (PM) is the main component of Baijiu (traditional Chinese liquor), and its microorganisms are the primary sources of the aroma of Chinese strong-flavor Baijiu (SFB). Enrichment plays an important role in the selection of functional microorganisms in PM. Herein, the PM of SFB was submitted to six rounds of enrichment using clostridial growth medium (CGM), and changes in the metabolite accumulation and microbiota composition were evaluated. Based on the metabolite production and microbiota composition, the enrichment rounds were classified as the acclimation stage (round 2), main fermentation stage (rounds 3 and 4), and late fermentation stage (rounds 5 and 6). Species within the genus Clostridium dominated in the acclimation stage (65.84-74.51%). In the main fermentation stage, the dominant microbial groups were producers of butyric acid, acetic acid, and caproic acid, which included Clostridium (45.99-74.80%), Caproicibacter (1.45-17.02%), and potential new species within the order of Oscillataceae (14.26-29.10%). In the late stage of enrichment, Pediococcus dominated (45.96-79.44%). Thus, the main fermentation stage can be considered optimal for the isolation of acid-producing bacteria from PM. The findings discussed herein support the development and application of functional bacteria by bioaugmentation, and contribute to improving the quality of PM and SFB production.

Bacterial Communities Found in Pit-Wall Mud and Factors Driving Their Evolution

Pit-wall mud (PWM) fosters bacterial communities involved in Baijiu production. PWM varies depending on pit age and height. In this study, we explored the bacterial communities in PWM and factors driving their evolution. The abundance and diversity of bacterial communities were low in new PWM (NPWM). In old PWM (OPWM), similar but diverse bacterial communities were observed at different heights. Lactobacillus was the predominant genus in NPWM, and Caproiciproducens, Aminobacterium, Hydrogenispora, Lactobacillus, Petrimonas, Syntrophomonas, and Sedimentibacter were the dominant genera in OPWM. A decrease was noted in the abundance of Lactobacillus, which indicated evolution. Among all the physicochemical properties, pH had the highest degree of interpretation with an R2 value of 0.965. pH also exerted the strongest effect on bacterial communities. The path coefficients of pH on bacterial community diversity and abundance were 0.886 and 0.810, respectively. Caproiciproducens and Clostridium sensu stricto 12 metabolized lactic acid, inhibiting the growth of Lactobacillus at a suitable pH, which led to the maturation of PWM. Our findings enrich the literature on the evolution of bacterial communities in PM and the maturation of PM.

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.

The co-occurrence network patterns and keystone species of microbial communities in cattle manure-corn straw composting

Microbes often form complex ecological networks in various habitats. Co-occurrence network analysis allows exploring the complex community interactions beyond the community diversities. This study explores the interspecific relationships within and between bacterial and fungal communities during composting of cow manure using co-occurrence network analysis. Furthermore, the keystone taxa that potentially exert a considerable impact on the microbiome were revealed by network analysis. The networks in the present study harbored more positive links. Specifically, the interactions/coupling within bacterial communities was tighter and the response to changes in external environmental conditions was more quickly during the composting process, while the fungal network had a better buffer capacity for changes in external environmental conditions. Interestingly, this result was authenticated in the bacterial-fungal (BF) network and the Mantel test of major modules and environmental variables. More than that, the Zi-Pi plot revealed that the keystone taxa including "module hubs" and "connectors" were all detected in these networks, which could prevent the dissociation of modules and networks.

Bacterial diversity associated with volatile compound accumulation in pit mud of Chinese strong-flavor baijiu pit

Pit mud quality is a key parameter that impacts the quality of Chinese strong-flavor Baijiu production.This study was developed to explore spatial bacterial community distributions and the relationships between these distributions and the volatile compound accumulation within the pit mud used in the production of Chinese strong-flavor Baijiu. The results revealed Lactobacillus pasteurii and Limnochorda pilosa were found to be the dominant bacteria present in the upper wall, middle wall, and bottom pit mud layers, whereas the Clostridium genus was detectable at high levels in the lower layer of the pit wall and played a role in contributing to the overall aroma and flavor compounds in produced Chinese strong-flavor Baijiu, with Clostridium abundance being strongly correlated with caproic acid, ethyl caproate, ethyl butyrate, and hexanol levels as well as moderately correlated with butyric acid levels. The abundance of the Lactobacillus genus was positively correlated with levels of ethyl lactate, 1-butanol, and 2,3-butanediol. Limnochorda pilosa was closely associated with ethyl acetate levels. Additionally, the correlations between bacterial communities and chemical properties also investigated, and the results demonstrated PO4^3-, total carbon, K⁺, humus, NH₄⁺-N, and Mg²⁺ levels significantly affected the bacterial community structure of pit mud, and they were positively correlated with the relative abundance of Clostridium. Together, these findings can serve as a foundation for future studies exploring the mechanisms whereby volatile compounds accumulate in different pit mud layers, which facilitates the fermentation regulation and pit mud quality improvement of Chinese strong-flavor Baijiu.

Analysis of bacterial diversity and functional differences of Jiang-flavored Daqu produced in different seasons

High-temperature Daqu is an important saccharifying fermenting starter for brewing Jiang-flavored Baijiu. This paper analyzed the diversity characteristics of bacterial communities of Jiang-flavored Daqu (JFDQ) with seasonal changes through Illumina HiSeq sequencing and multivariate statistical methods. Results showed that 21 phyla, 529 genera, and 47 core bacterial genera were identified from the 48 composite samples. Among them, eight functional genera were only found in the summer-produced Daqu (Propionigenium, etc.). Pantoea, Bacillus, Lentibacillus, and Oceanobacillus, respectively, served as the representative functional bacterial genera of the four seasons. Functional prediction analysis showed that Amino acid metabolism Carbohydrate metabolism, Lipid metabolism, Metabolism of cofactors and vitamins, and Nucleotide metabolism (relative abundance > 1%) were the most critical microbial functions in JFDQ, and these key enzymes involved in acetoin biosynthesis, and acetyl-CoA biosynthesis were more abundant in the summer than in the winter. The functional microorganisms community in this paper would provide valuable suggestions about the seasonal production of JFDQ, guiding the Baijiu brewing processes.

Carbon sequestration from refractory dissolved organic carbon produced by biodegradation of Saccharina japonica

Using macroalgae cultures to sequester carbon has been proposed in recent years. Yet the key mechanism of carbon sequestration-how carbon in degrading biomass is converted into refractory dissolved organic carbon (RDOC) remains poorly understood. The process of producting RDOC via biomass degradation of Saccharina japonica, the most productive algae in China, was thus studied in the laboratory. Most of the carbon in the kelp biomass was converted to dissolved inorganic carbon (DIC) by bacterial respiration. Only 7.8% of the carbon in the kelp biomass was converted into labile DOC, semi-labile or semi-refractory DOC, and refractory DOC in turn. The enrichment of DIC resulted in hypoxic conditions in the water. For the hypoxia in the experiment, the sulfur-degrading bacteria Campylobacteria and Bacteroidia became the dominant bacterial classes, which were the key drivers for the transformation of labile DOC to semi-labile or semi-refractory DOC. Then, semi-labile or semi-refractory DOC was converted to RDOC, driven by the sulfite-reducing bacteria Clostridia and Kapabacteria. Finally, 0.3% of the carbon content in kelp was transformed into RDOC. The resulting RDOC, which was rich in sulfur and nitrogen elements, increased the molecular diversity and average molecular weight in the water. An important finding was that the production of RDOC may be accompanied by the environmental risk of hypoxia.

Seasonal dynamics of microbiota and physicochemical indices in the industrial-scale fermentation of Sichuan Baoning vinegar

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Differences between the microbiomes in every-two seasons were observed.

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The increase in total acidity of vinegar Pei was lowest in the summer (3.40 g/100 g).

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Lactic acid and acetic acid contents in raw vinegar from each season were different.

We investigated the impact of seasons of the year on microbiota and physicochemical indices in industrial-scale fermentation of Sichuan Baoning vinegar. Illumina HiSeq sequencing results showed significant differences (P < 0.05) between the microbiomes of vinegar Pei in every-two seasons, except for bacterial communities between summer and autumn. Total acid, reducing sugar, starch, and alcohol contents of vinegar Pei from the same sampling day of each season were measurably different. Although total acid content in vinegar Pei was similar at the end of fermentation (P > 0.05), the increase in total acidity was highest in the autumn. Acetic acid content in raw vinegar was highest in the autumn (3472.42 mg/100 mL), and lowest in the summer (2304.01 mg/100 mL). This study provides a theoretical basis for the production of Sichuan bran vinegar with consistent quality and provides insights into the quality control of traditional fermented foods.

Systematic Review of Actinomycetes in the Baijiu Fermentation Microbiome

Actinomycetes (a group of filamentous bacteria) are the dominant microbial order in the Daqu (DQ) fermentation starter and in the pit mud (PM) of the Baijiu fermentation microbiome. Actinomycetes produce many of the key enzymes and flavor components, and supply important precursors, which have a major influence on its characteristic aroma components, to other microorganisms during fermentation. This paper reviews the current progress on actinomycete research related to Baijiu fermentation, including the isolation and identification, distribution, interspecies interactions, systems biology, and main metabolites. The main metabolites and applications of the actinomycetes during Baijiu fermentation are also discussed.

Proteiniphilum propionicum sp. nov., a novel member of the phylum Bacteroidota isolated from pit clay used to produce Chinese liquor

A novel, Gram-stain-negative, rod-shaped, strictly anaerobic bacterium of genus Proteiniphilum of the phylum Bacteroidota, named strain JNU-WLY501^T, was isolated from pit clay used to produce strong aroma-type liquor in PR China. The genomic DNA G+C content and genome size of JNU-WLY501^T were 41.4 % and 3.9 Mbp, respectively. The results of phylogenetic analysis based on 16S rRNA gene sequences indicated that JNU-WLY501^T was closely related to Proteiniphilum acetatigenes DSM 18083^T (95.7 %) and Proteiniphilum saccharofermentans M3/6^T (94.9 %). The pairwise average nucleotide identity based on blast and average amino acid identity values of JNU-WLY501^T compared with Proteiniphilum saccharofermentans M3/6^T were 73.6 and 77.3 %, respectively, which both were lower than the threshold values for bacterial species delineation. The strain grew at 20-40 °C, with optimum growth at 37 °C. The pH range for growth was 5.4-9.1, with optimum growth at pH 7.5. The sodium chloride range for growth was 0.0-4.0 %, with optimum growth at 0 %. The strain did not use glucose, maltose, fructose or starch. Yeast extract, tryptone and peptone supported the growth of JNU-WLY501^T, and the main fermentation products were acetate and propionate. The predominant cellular fatty acids (>5 %) of JNU-WLY501^T were anteiso-C_15 : 0 (30.6 %), anteiso-C_17 : 0 (26.1 %), C_16 : 0 (7.7 %), iso-C_16 : 0 (5.0 %) and iso-C_17 : 0 (5.0 %). The respiratory quinone of JNU-WLY501^T was MK-5. On the basis of the morphological, physiological, biochemical, chemotaxonomic, genotypic and phylogenetic results, JNU-WLY501^T represents a novel species of the genus Proteiniphilum, for which the name Proteiniphilum propionicum sp. nov. is proposed. The type strain is JNU-WLY501^T (=GDMCC 1.2686^T=JCM 34753^T).

Effects of Daqu Attributes on Distribution and Assembly Patterns of Microbial Communities and Their Metabolic Function of Artificial Pit Mud

Daqu provides functional microbiota and various nutrients for artificial pit mud (APM) cultivation. However, little is known about whether its attributes affect the microbiome and metabolome of APM. Here, two types of APM were manufactured by adding fortified Daqu (FD) and conventional Daqu (CD); they were comprehensively compared by polyphasic detection methods after being used for two years. The results showed that FD altered the prokaryotic communities rather than the fungal ones, resulting in increased archaea and Clostridium_sensu_stricto_12 and decreased eubacteria and Lactobacillus. Correlation analysis suggested that these variations in community structure promoted the formation of hexanoic acid, butyric acid, and the corresponding ethyl esters, whereas they inhibited that of lactic acid and ethyl lactate and thus improved the flavor quality of the APM. Notably, pH was the main driving factor for the bacterial community variation, and the total acid mediated the balance between the stochastic and the deterministic processes. Furthermore, the results of the network analysis and PICRUSt2 indicated that FD also enhanced the modularity and robustness of the co-occurrence network and the abundance of enzymes related to hexanoic acid and butyric acid production. Our study highlights the importance of Daqu attributes in APM cultivation, which are of great significance for the production of high-quality strong-flavor Baijiu.

Effect of microbial interaction on flavor quality in Chinese baijiu fermentation

Chinese baijiu brewing is an open, complex, and synergetic functional microbiota fermentation process. Microbial interaction is pivotal for the regulation of microbial structure and function in the brewing microecosystem, consequently affecting the flavor and quality of baijiu. This article mainly summarizes the effect of microbial interactions among functional microbiota on the growth performance, flavor formation, and safe quality of baijiu fermentation process. In addition, the review specifically emphasizes on the microbial interactions for the regulation of “Ethyl Caproate-Increasing and Ethyl Lactate-Decreasing” in Chinese strong-flavor baijiu. Furthermore, the construction of synthetic microbiota by metabolic characteristics of the functional microbes and their interactions for regulating and controlling flavor quality of Chinese baijiu is also reviewed and prospected.

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.

Analysis of bacterial diversity and genetic evolution of Lacticaseibacillus paracasei isolates in fermentation pit mud

AIMS

Since little is known about the genetic diversity of lactic acid bacteria (LAB) isolates from the fermentation pit mud (FPM), we sought to evaluate the bacterial structure, identify the LAB isolates and investigate the genotype and genetic diversity of the LAB isolates.

METHODS AND RESULTS

Using high-throughput MiSeq sequencing, we identified seven dominant bacterial genera in FPM. Lactobacillus had the highest abundance. We isolated 55 LAB strains. These isolates were all identified as Lacticaseibacillus paracasei. Using an extant multilocus sequence typing (MLST) scheme, isolates were assigned to 18 sequence types (STs) and three clonal complexes. ST1, the largest group, mainly comprised FPM isolates. Niche-specific ST2 to ST18 only contained FPM isolates. Isolates could be divided into four lineages, with most assigned to Lineage 1. Only one FPM isolate was classified as L. paracasei subsp. paracasei. Other isolates could not be classified at the subspecies level using the seven MLST loci.

CONCLUSIONS

Lactobacilli account for a high proportion of bacteria in pit mud. Based on the traditional culture method, L. paracasei was the dominant species, and these isolates exhibit a high ethanol tolerance, high intraspecific diversity and specific genetic profiles.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study described the characterization of FPM bacterial diversity, giving an insight into the genetic diversity of L. paracasei strains present in FPM.

Effects of Different Daqu on Microbial Community Domestication and Metabolites in Nongxiang Baijiu Brewing Microecosystem

The quality and yield of the fresh Baijiu mainly depend on the activity of pit mud (PM) and the quality of Daqu. However, the cultivation of PM is a long-term process, and high-quality Daqu can change the community structure of fermented grain (FG) and accelerate the evolution of PM communities. The present research aimed to investigate the four different types of Daqu on the FG-fermenting microbial community structure and metabolites and their interphase interactions with PM. These results show that Kroppenstedtia in the bacterial community of Taikong Daqu (TK) was positively correlated with ethyl caproate, which significantly increased the content of FG volatile metabolites, especially lipid components, and facilitated the accelerated evolution of Methanobacteriales and Methanosarcinales in PM. Bacillus has a high relative abundance in Qianghua Daqu (QH), which shows obvious advantages to improving the alcoholic strength of FG and contributing to increasing the abundance of Methanomicrobiales in PM. Qianghua and traditional-mixed Daqu (HH) have a similar bacterial composition to QH and a similar fungal composition to traditional Daqu (DZ), and thus also showed the advantage of increased yield, but the volatile flavor metabolites produced were not as dominant as DZ. β-diversity analysis showed that in TK fermentation systems, FG is more likely to domesticate the structure of PM microorganisms. These results indicated that the interaction between microbial communities in Baijiu fermentation niches was significantly influenced by different Daqu. It can not only enhance the key volatiles in FG but also accelerate the evolving direction of the community in PM. Daqu fortified by functional genera or microbiota can evolve a community structure more suitable for Baijiu fermentation. The microbiota composition and interaction between the communities in both Daqu and PM significantly impacts the yield and quality of the base liquor.

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.

Deep sequencing reveals changes in prokaryotic taxonomy and functional diversity of pit muds in different distilleries of China

Purpose

The microbial community in the pit mud correlated closely with the quality of the final product of Chinese strong-flavored Baijiu (CSFB). However, environmental conditions and brewing processes can vary by region and distilleries. This may lead to differences in microbial composition and function in pit mud. Therefore, revealing the features of the pit mud microbial community structure and functions of different distilleries will provide key information for understanding the diversity and difference of microbes in the brewing of CSFB, which will be beneficial for the improvement of the quality of pit mud and CSFB in the future.

Methods and results

Illumina MiSeq sequencing of 16S rRNA gene amplicons was used to analyze the similarities and differences in microbial community structure and function in pit muds of different distilleries located in Shihezi (Xinjiang), Xiangyang (Hubei), and Yibin (Sichuan). At the genus level, Clostridium, Lactobacillus, Aminobacterium, Petrimonas, Syntrophomonas, Methanoculleus, Syntrophaceticus, Sedimentibacter, Caloramator, Ruminococcus, Bacillus, Methanosarcina, and Garciella were the dominated genera of pit muds. There were great differences in the composition of microorganisms in pit muds used by different distilleries. The significantly enriched prokaryotic microbiotas of pit muds collected in the distilleries of Xiangyang were mainly affiliated with Bacillus, Lactobacillus, and Croceifilum, and the relative abundance of methanogens, such as Methanomicrobia and Methanobacteria, were only significantly enriched in the pit mud collected from the distilleries of Yibin (P < 0.05). Functional analysis indicated that the difference of microbial composition in pit mud will further lead to significant differences in various metabolic functions.

Conclusion

The compositions and functions of dominant microorganisms in pit mud used for the production of CSFB by different enterprises across regions in China were greatly different, and there was a close relationship between the compositions and functions of microorganisms in pit mud. Therefore, it may be an effective method to improve CSFB fermentation processes by directionally regulating the microbial community functions of pit mud using specific strains.

Microbial community spatial structures in Luzhou-flavored liquor pit muds with different brewing materials

Background

Although studies have shown that Bacteroidetes, Clostridiales, and Lactobacillales are the main components of the microbial community in pit mud during the brewing of Luzhou-flavored liquor, little is known about the effect of brewing materials on spatial structures of this microbiome.

Methods

High-throughput sequencing of the V4-V5 region of prokaryotic 16S rRNA gene was performed to analyze the microbial community diversity and spatial heterogeneity in Luzhou-flavored liquor pit muds with different brewing ingredients. The structural characteristics and heterogeneous spatial distribution of the pit mud microbial communities were examined using bioinformatics and multivariate statistical analysis methods.

Results

Our results showed that Euryarchaeota, Actinobacteria, Bacteroidetes, Chlorobi, Chloroflexi, Firmicutes, Proteobacteria, Synergistetes, Tenericutes, and WWE1 were the dominant phyla in the pit mud microbiome. The Shannon and Simpson indices of the pit mud microbiome with three grains (M3G) in the upper layer were significantly lower than those in middle layer and bottom, whereas those of the pit mud microbiome with five grains (M5G) in bottom were significantly lower than those in middle layer (p < 0.05). There were significant differences in the microbial community compositions between the pit muds with different brewing ingredients and locations in the same pit (p < 0.05). T78 of Anaerolinaceae, Butyrivibrio, Dehalobacter_Syntrophobotulus, Desulfosporosinus, Asteroleplasma, and vadinCA02 of Synergistaceae were significantly enriched in M3G, whereas Prevotella, Vagococcus, Caldicoprobacter, Butyrivibrio, Coprococcus, Dorea, Sporanaerobacter, Tepidimicrobium, TissierellaSoehngenia, RFN20 of Erysipelotrichaceae, Sutterella, 125ds10 of Alteromonadales, Vibrio, and Sphaerochaeta were significantly enriched in M5G. This study provides a theoretical basis for exploring the influence of brewing ingredients in pit muds on the production of Luzhou-flavored liquor and the specific influence of pit mud microorganisms in different locations on liquor production.

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.

The amino acids, bacterial communities, and their correlations in Wuliangye-flavour liquor production

With the enhancement of people’s awareness of drinking health, the health factors in Wuliangye-flavour liquor is worth our attention. Bacterial communities in 4 layers of Zaopei from the same fermentation pit and amino acids as major health factors in 4 liquors directly related Zaopeis were investigated by Illumina MiSeq sequencing and liquid chromatography mass spectrometry, respectively. Results indicated that 18 amino acids were detected and 8 dominant bacteria (genus level) were observed. Meanwhile, total amino acids, 11 amino acids (Glu, Asp, Val, etc), bacterial diversity, and the percentages of Lactobacillus and Pseudomonas increased with the increase of Zaopei’s depth; 5 amino acids (Pro, Ser, Phe, etc) and the percentages of Pediococcus and Bacteroides first increased and then decreased with the increase of Zaopei’s depth. Moreover, 11 amino acids were significantly (P < 0.01) and strongly (|ρ| > 0.8) positively correlated with Lactobacillus and Pseudomonas numbers.

The Depth-Depended Fungal Diversity and Non-depth-Depended Aroma Profiles of Pit Mud for Strong-Flavor Baijiu

Microorganisms in pit mud are the essential factor determining the style of strong flavor Baijiu. The spatial distribution characteristics of fungal communities and aroma in the pit mud for strong flavor Baijiu from Xinjiang, China, were investigated using Illumina MiSeq high-throughput sequencing and electronic nose technology. A total of 138 fungal genera affiliated with 10 fungal phyla were identified from 27 pit mud samples; of these, Saccharomycopsis, Aspergillus, and Apiotrichum were the core fungal communities, and Aspergillus and Apiotrichum were the hubs that maintain the structural stability of fungal communities in pit mud. The fungal richness and diversity, as well as aroma of pit mud, showed no significant spatial heterogeneity, but divergences in pit mud at different depths were mainly in pH, total acid, and high abundance fungi. Moisture, NH4 +, and lactate were the main physicochemical factors involved in the maintenance of fungal stability and quality in pit mud, whereas pH had only a weak effect on fungi in pit mud. In addition, the fungal communities of pit mud were not significantly associated with the aroma. The results of this study provide a foundation for exploring the functional microorganisms and dissecting the brewing mechanism of strong flavor Baijiu in Xinjiang, and also contributes to the improvement of pit mud quality by bioaugmentation and controlling environmental physicochemical factors.