Physiological characterization and safety assessment of thermotolerant Lodderomyces elongisporus in sauce-flavored Daqu: based on genomic insight

The fermentation temperature of sauce-flavored high-temperature Daqu can reach 65 °C, where microbial diversity and abundance are closely associated with liquor yield and quality. This study aimed to isolate thermotolerant yeast strains from sauce-flavored high-temperature Daqu and investigate their tolerance mechanisms and safety profiles. Using sauce-flavored Daqu as material, culturable methods were applied for yeast isolation and screening, followed by whole-genome sequencing analysis. The biological characteristics were examined, and gain an in-depth understanding of their high-temperature resistance mechanisms and characteristics. A thermotolerant yeast strain L253 was isolated and identified as Lodderomyces elongisporus, exhibiting maximum temperature tolerance at 55 °C with optimal growth at 45 °C, pH tolerance of 3-8, alcohol tolerance up to 6.8% (v/v), and sugar tolerance reaching 80% (w/v). Safety assessments demonstrated weak nitrate reductase activity, non-hemolytic properties, and negative indole test, confirming its safety. The genome (GenBank: PRJNA1185419) measured 16,118,111 bp with 37.3% G + C content, containing 5,102, 4,170, 3,390 and 5,380 annotated genes in eggNOG, GO, KEGG and NR databases respectively. Thermotolerance-related genes included HSFF, HSP70 and its interacting proteins (HSPBP1, HSPA5/BiP), and HSP90, while osmotolerance involved gpd and gpp genes. In this study, the phenotype and genotype of strain L253 were analyzed to increase the understanding of microbial functions in the high-temperature Daqu environment, and reveal the potential value of this strain in industrial fermentation.