Caproicibacterium argilliputei sp. nov., a novel caproic acid producing anaerobic bacterium isolated from pit clay

Composition and metabolite patterns of caproic acid-producing bacteria during pH-mediated pitmud-Huangshui co-fermentation based on multi-database annotation

The growth and metabolism of caproic acid - producing bacteria (CPBs) in the pit mud (PM) within the Huangshui (HS) are crucial for both the quality of Chinese Nongxiangxing Baijiu (NXXB) fermentation and the aging of the PM. Based on multi-database co-annotation and key affecting factors identification of CPBs, the growth and metabolites pattern of CPBs was studied through the pH-mediated PM-HS co-fermentation. CPBs in PM were mainly from Oscillospiraceae family. The composition and metabolites profiles of CPBs changed with initial pH-adjustment. Lactobacillus (88.61 %-89.41 %) dominated the PM-HS system at an initial pH of 5, with CPBs suppressed. Butyric acid-producing Clostridium (56.18 %-54.53 %, 19.61 %-42.71 %) and CPBs (9.35 %-5.19 %, 65.44 % 50.01 %) co-dominated the PM-HS system with initial pH values of 6 and 7 respectively. This study may help illuminate the role of CPBs in PM aging, facilitating the targeted CPBs-enrichment, unknown CPBs-isolation, and practical regulation of CPBs-bioaugmentation in NXXB ecosystem.

Identification of volatile differential markers in strong-aroma Baijiu based on gas chromatography-electronic nose combined with gas chromatography-time-of-flight mass spectrometry

BACKGROUND

Baijiu is a traditional Chinese liquor produced from grains through fermentation, distillation, aging and blending. The flavor of Baijiu is influenced by factors such as raw materials, starter, processes and the environment, and since the relationship between these factors and the flavor of Baijiu is still being analyzed, the identification of different Baijiu is still somewhat difficult. In this paper, the volatile differential markers of 42 types of strong-aroma Baijiu of different origin, alcohol content and grade were explored.

RESULTS

A total of 24 volatile substances were detected by gas chromatography-electronic nose (GC-E-Nose) and 99 volatile substances were detected by gas chromatography-time-of-flight mass spectrometry (GC-TOF MS). The peak areas of the substances obtained by GC-E-Nose were analyzed by the partial least squares (PLS) method, and the substances with variable importance in projection (VIP) >1 were screened out. Combined with the qualitative results of GC-TOF MS, four substances (isobutyric acid, 2-butanone, 2,3-butanediol and 3-methylbutyric acid) were selected as volatile differential markers for strong-aroma Baijiu. An external standard curve was established to accurately quantify these four substances, and the Kruskal-Wallis test confirmed that the absolute contents of these four substances varied significantly among different samples (P < 0.01). Principal component analysis and hierarchical cluster analysis based on the absolute content of these four substances showed that different samples were prioritized for different alcohol contents.

CONCLUSION

These four substances can be used as volatile differential markers of strong-aroma Baijiu samples. This research provides theoretical support for the detection and improvement of Baijiu product quality. © 2024 Society of Chemical Industry.

Uncovering new Firmicutes species in vertebrate hosts through metagenome-assembled genomes with potential for sporulation

Metagenome-assembled genomes (MAGs) have contributed to identifying non-culturable microorganisms and understanding their ecological functions. MAGs offer an advantage in investigating sporulation-associated genes, especially given the difficulty of isolating many species residing in the gut microbiota of multiple hosts. Bacterial sporulation is a key survival mechanism with implications for pathogenicity and biotechnology. Here, we investigate MAGs from vertebrate hosts, emphasizing taxonomic identification and identifying sporulation-associated genes in potential novel species within the Firmicutes phylum. We identified potential new species in the classes Clostridia (Borkfalkiaceae, Lachnospiraceae, Monoglobaceae, and Oscillospiraceae families) and Bacilli (Bacillaceae and Erysipelotrichaceae families) through phylogenetic and functional pathway analyses, highlighting their sporulation potential. Our study covers 146 MAGs, 124 of them without refined taxonomic assignments at the family level. We found that Clostridia and Bacilli have unique sporulation gene profiles in the refined family MAGs for cattle, swine, poultry, and human hosts. The presence of genes related to Spo0A regulon, engulfment, and spore cortex in MAGs underscores fundamental mechanisms in sporulation processes in currently uncharacterized species with sporulation potential from metagenomic dark matter. Furthermore, genomic analyses predict sporulation potential based on gene presence, genome size, and metabolic pathways involved in spore formation. We emphasize MAGs covering families not yet characterized through the phylogenetic analysis, and with extensive potential for spore-forming bacteria within Clostridia, Bacilli, UBA4882, and UBA994 classes. These findings contribute to exploring spore-forming bacteria, which provides evidence for novel species diversity in multiple hosts, their adaptive strategies, and potential applications in biotechnology and host health.IMPORTANCESpores are essential for bacterial survival in harsh environments, facilitating their persistence and adaptation. Exploring sporulation-associated genes in metagenome-assembled genomes (MAGs) from different hosts contributes to clinical and biotechnological domains. Our study investigated the extent of genes associated with bacterial sporulation in MAGs from poultry, swine, cattle, and humans, revealing these genes in uncultivated bacteria. We identified potential novel Firmicutes species with sporulation capabilities through phylogenetic and functional analyses. Notably, MAGs belonging to Clostridia, Bacilli, and unknown classes, namely UBA4882 and UBA994, remained uncharacterized at the family level, which raises the hypothesis that sporulation would also be present in these genomes. These findings contribute to our understanding of microbial adaptation and have implications for microbial ecology, underlining the importance of sporulation in Firmicutes across different hosts. Further studies into novel species and their sporulation capability can contribute to bacterial maintenance mechanisms in various organisms and their applications in biotechnology studies.

Characteristics and Functions of Dominant Yeasts Together with Their Applications during Strong-Flavor Baijiu Brewing

Yeasts are pivotal brewing microbes that are associated with the flavor and quality of Chinese baijiu, yet research on dominant yeasts in strong-flavor baijiu brewing remains limited. In this study, Saccharomyces cerevisiae, Pichia kudriavzevii, and Kazachstania bulderi were identified as predominated yeasts in strong-flavor baijiu. Each strain showed distinct characteristics in ethanol resistance, thermal tolerance, and lactic acid tolerance, severally. S. cerevisiae FJ1-2 excelled in ethanol and ethyl ester production, P. kudriavzevii FJ1-1 in ethyl acetate, and K. bulderi FJ1-3 in lactic acid generation. Subsequently, the reinforced Fuqu of each yeast were severally prepared for application in baijiu brewing to verify their functions. Results revealed that the relative abundance of fortified yeast in each group rose. Pichia, Kazachstania, and Saccharomyces emerged as the core microbe for each group, respectively, by co-occurrence network analysis, influencing the microbiota to regulate flavor substances. In short, P. kudriavzevii FJ1-1 enhanced ethyl acetate. K. bulderi FJ1-3 improved ethyl caproate production and decreased levels of ethyl acetate and higher alcohols by modulating yeast community between Pichia and Saccharomyces. This is a systematic endeavor to study the functions of yeasts of strong-flavor baijiu, providing a solid basis for improving baijiu quality.

Recent progress and prospects for chain elongation of transforming biomass waste into medium-chain fatty acids

Chain elongation technology utilises microorganisms in anaerobic digestion to transform waste biomass into medium-chain fatty acids that have greater economic value. This innovative technology expands upon traditional anaerobic digestion methods, requiring abundant substrates that serve as electron donors and acceptors, and inoculating microorganisms with chain elongation functions. While this process may result in the production of by-products and elicit competitive responses, toxicity suppression of microorganisms by substrates and products remains a significant obstacle to the industrialisation of chain elongation technology. This study provides a comprehensive overview of existing research on widely employed electron donors and their synthetic reactions, competitive reactions, inoculum selection, toxicity inhibition of substrates and products, and increased chain elongation approaches. Additionally, it presents actionable recommendations for future research and development endeavours in this domain, intending to inspire and guide researchers in advancing the frontiers of chain elongation technology.