Construction of a safe and efficient synthetic microbial community for standardized fermentation of traditional...

Jiangshui, a traditional fermented vegetable food in Northwest China, suffers from unstable quality and difficulty in industrialization due to undefined natural fermentation. To address this, a synthetic microbial community (SynCom) via manual combination was constructed for standardized Jiangshui fermentation by combining screened LAB strains from traditional Jiangshui at ratios empirically optimized through evaluation of acidity, sensory quality, total phenols, and flavonoids. In this study, LAB were isolated and purified from 53 traditional Jiangshui samples collected from Gansu Province, and 5 dominant strains (Y-5-3, Y-6-2, HN, HX, CB) were screened via morphological, molecular and physiological characterization. These strains were systematically evaluated for growth performance, acid production capacity, stress tolerance, gastrointestinal tolerance, adhesion properties, antimicrobial activity, and biosafety (hemolytic activity, antibiotic susceptibility, virulence gene detection). On this basis, 3 high-performance strains (Y-5-3, Y-6-2, HN) were selected and manually combined in 20 ratios to construct SynComs, and fermentation effects were assessed by acidity, sensory quality, total phenol, and flavonoid contents. All 5 strains exhibited γ-hemolysis, no virulence genes, and good antibiotic susceptibility, confirming biosafety. Strain Y-5-3 showed optimal performance. The optimal fermentation scheme was Y-5-3: Y-6-2: HN = 2:3:1, achieving the highest sensory score (89.38 ± 4.10 points) and significantly increasing total phenols (72.20% higher, P < 0.01) and flavonoids (61.13% higher, P < 0.01) compared with natural Jiangshui, while reducing off-odors and improving stability. This study provides a scientific basis for industrialization and standardization of traditional Jiangshui production.