基于宏基因组解析中温大曲成熟前后的微生物群落功能差异

Metagenomics unveils the differences in the functions of microbial community of medium-temperature Daqu before and after maturation

摘要:

大曲是白酒酿造中的糖化发酵剂和生香剂，其成熟过程是获得高品质大曲的重要步骤。前期研究探索了大曲成熟前后的微生物群落组成和多样性，但对微生物群落功能的变化缺乏深入研究。本文在分析中温大曲成熟前后酶活和挥发性化合物的基础上，采用宏基因组学解析微生物群落组成和潜在功能的差异，并探索酶活和重要挥发性化合物变化的微生物基础。结果显示，大曲成熟后，水分含量(P≤0.05)、淀粉含量、液化力、糖化力(P≤0.05)和发酵力降低，而酸度和酯化力(P≤0.05)升高；同时，其挥发性化合物组成变化显著(P=0.001)，芳香醇类和芳香酯类物质含量显著降低，吡嗪类、酮类和高级脂肪醇类物质含量显著升高。成熟大曲中毛霉菌目(Mucorales，34.8%−23.0%)和散囊菌目(Eurotiales，34.3%−20.1%)等真菌相对丰度降低，功能分析表明这降低了α-淀粉酶、α-葡萄糖苷酶、乙醇脱氢酶和乙醇脱氢酶(NADP⁺)的基因丰度(P>0.05)，导致大曲液化力(P>0.05)、糖化力(P≤0.05)、发酵力(P>0.05)和苯乙醇等芳香醇类物质含量降低(P≤0.05)。此外，酵母菌目(Saccharomycetales，2.9%−16.6%)、乳杆菌目(Lactobacillales，14.9%−23.6%)和芽孢杆菌目(Bacillales，0.8%−3.8%)等微生物的相对丰度升高，使得乙酰基转移酶、羧酸酯酶、乙酰乳酸脱羧酶、R-乙偶姻脱氢酶和S-乙偶姻脱氢酶的基因丰度显著升高(P≤0.05)，进而显著提高了大曲的酯化力和吡嗪类物质含量(P≤0.05)。本文在基因水平解析了大曲成熟前后酶活和重要挥发性化合物变化的微生物基础，可为理性调控大曲生产提供理论支撑。

Abstract:

Daqu is the saccharifying, fermenting, and aroma-producing agent used in Baijiu brewing, and its maturation is crucial for obtaining high-quality Daqu. Previous studies have explored the microbial community composition and diversity before and after maturation. However, little is known about the changes in the functions of microbial community. In this study, based on the analyses of enzyme activities and volatile compounds of medium-temperature Daqu before and after maturation, metagenomics was used to analyze the differences in the composition of microbial community and the potential functions, with the aim to explore the microorganisms involved in changes in enzyme activities and important volatiles. The results showed that the moisture (P≤0.05), starch content, liquefying activity, saccharifying activity (P≤0.05), and fermentative activity decreased, while the acidity and esterifying activity (P≤0.05) increased after Daqu maturation. In the meantime, the composition of volatile compounds changed significantly (P=0.001), with significant decreases in the contents of aromatic alcohols and esters as well as significant increases in the contents of pyrazines, ketones, and higher fatty alcohols. The relative abundances of Mucorales (34.8%−23.0%) and Eurotiales (34.3%−20.1%) decreased in matured Daqu, and functional predictions showed these changes decreased the gene abundances of α-amylase, α-glucosidase, alcohol dehydrogenase, and alcohol dehydrogenase (NADP⁺) (P>0.05), resulting in lower levels of liquefying activity (P>0.05), saccharifying activity (P≤0.05), fermentative activity (P>0.05), as well as aromatic alcohols such as phenylethyl alcohol (P≤0.05). In addition, higher relative abundances of Saccharomycetales (2.9%−16.6%), Lactobacillales (14.9%−23.6%), and Bacillales (0.8%−3.8%) were observed after maturation, and they were conducive to improving the gene abundances of alcohol O-acetyltransferase, carboxylesterase, acetolactate decarboxylase, (R)-acetoin dehydrogenase, and (S)-acetoin dehydrogenase (P≤0.05), resulting in significantly higher levels of esterifying activity and pyrazines (P≤0.05). The microorganisms involved in the changes in enzyme activities and important volatiles before and after Daqu maturation were studied at the gene level in this work, which may facilitate further rational regulation for Daqu production.