Synthetic microbial community converts corn stover hydrolysate into high-purity L-lactic acid in the presence of fermentation inhibitors.

Lignocellulosic hydrolysates contain inhibitors that hinder lactic acid (LA) production. This study evaluated a synthetic microbial community (SMC) of five lactic acid bacteria for fermenting undetoxified corn stover hydrolysate. Metatranscriptome analysis revealed links between fermentation performance and inhibitor effects. Although LA yield decreased by 5.79% versus the control, SMC achieved 94.47% mixed sugar utilization and produced L-LA with 99.70% optical purity. Transcriptomic data suggest that hydrolysate inhibitors may suppress glycolysis and the pentose phosphate pathway, which may contribute to a shift in carbon flux to the TCA cycle. Upregulation of malolactic enzyme (mleA) and downregulation of D-lactate dehydrogenase/hydroxyacylglutathione hydrolase (ldhA/gloB) correlated with enhanced L-LA purity. Syringaldehyde showed the strongest inhibition among tested compounds. These findings demonstrate an effective SMC-based strategy for producing high-purity L-LA from undetoxified hydrolysates, advancing biomass utilization.