Deciphering the D-/L-lactate-producing microbiota and manipulating their accumulation during solid-state fermentation of cereal vinegar

Symphony orchestra of multi-microorganisms characterizes the solid-state acetic acid fermentation process of Chinese cereal vinegars. Lactate is the predominant non-volatile acid and plays indispensable roles in flavor formation. This study investigated the microbial consortia driving the metabolism of D-/L-lactate during fermentation. Sequencing analysis based on D-A-lactate dehydrogenase genes demonstrated that L-actobacillus (relative abundance: > 95%) dominated the production of both D-lactate and L-lactate, showing species-specific features between the two types. Lactobacillus helveticus (> 65%) and L. reuteri (-80%) respectively dominated Land D-lactate-producing communities. D-A-lactate production and utilization capabilities of eight predominant Lactobacillus strains were determined by culture-dependent approach. Subsequently, D-/L-lactate producer L. plantarum M10-1 (D:L approximate to 1:1), L-lactate producer L. casei 21M3-1 (D:L approximate to 0.2:9.8) and D-/L-lactate utilizer Acetobacter pasteurianus G3-2 were selected to modulate the metabolic flux of D-/L-lactate of microbial consortia. The production ratio of D-/L-lactate was correspondingly shifted coupling with microbial consortia changes. Bioaugmentation with L. casei 21M3-1 merely enhanced L-lactate production, displaying similar to 4-fold elevation at the end of fermentation. Addition of L. plantarum M10-1 twice increased both D- and L-lactate production, while A. pasteurianus G3-2 decreased the content of D-/L-isomer. Our results provided an alternative strategy to specifically manipulate the metabolic flux within microbial consortia of certain ecological niches.