Oceanobacillus in high-temperature Daqu: Taxonomic diversity, metabolic characteristics and biofortification effect

Abstract

High-temperature Daqu (HTD) is a critical component in Jiang-flavor Baijiu production, supplying flavor precursors, enzymes, and diverse microorganisms. Notably, HTD harbors Oceanobacillus, an ecological generalist whose role in the microecosystem remains to be defined. Here, we first identified 21 amplicon sequence variants (ASVs) belonging to six Oceanobacillus species in 20 HTD samples through 16S rRNA gene sequencing. Subsequently, representative strains of eight Oceanobacillus species were selectively isolated from HTD using predicted culture media. These strains exhibited potent enzymatic activities including cellulase and neutral proteinase, alongside diverse metabolic capabilities. Furthermore, we evaluated the impact of Oceanobacillus caeni, the predominant species, on HTD fermentation. Compared to the control, the relative abundance of Oceanobacillus caeni in the biofortified HTD increased significantly, from 3.82 % to 10.25 %, with the biomass of Oceanobacillus caeni surged from 5.15 × 10⁸ to 2.95 × 10⁹ copies/g. The activities of cellulase and neutral proteinase in the biofortified HTD escalated to 1.20 U and 57.14 U, respectively. The levels of volatile pyrazines and phenols in the biofortified HTD increased by 1.45 and 1.55 times, respectively. Levels of other volatiles including isovaleraldehyde, furfural, isobutyric acid, phenylacetone, ethyl palmitate, and 1,2-dimethoxybenzene saw respective increases of 3.77, 2.26, 1.94, 2.21, 5.21, and 2.27 times. This study sheds light on the role of Oceanobacillus in HTD, offering a theoretical foundation for improving Daqu quality.