Valorization of vegetable waste into a lactate-rich soil amendment via simultaneous saccharification and fermentation...

Lignocellulose represents a major renewable carbon source in vegetable waste (VW), but recalcitrant structure severely impedes fermentable sugar release, thereby hindering efficient simultaneous saccharification and fermentation (SSF). To address this, a functional microbial consortium was constructed for efficient lignocellulose degradation during the SSF of VW. After 72 h of fermentation, the consortium achieved a lignocellulose degradation rate of 22.28% and produced 0.788 g/g of lactic acid (LA) from dry VW, representing a 123.24% increase compared to the uninoculated control. The resulting fermentation product, rich in organic matter, polyphenols, and proteases, significantly enhanced soil urease and sucrase activities following a 28-day soil application. Soil total nitrogen, available phosphorus, and available potassium increased by 49.71%, 211.59%, and 84.62%, respectively. Bacillus amyloliquefaciens Z3, as the key lignocellulose-degrading strain within the consortium, was revealed by transcriptomic analysis to significantly upregulated multiple CAZymes genes encoding glycosyltransferases and glycoside hydrolases during SSF. This strain primarily degraded cellulose via the synergistic action of endoglucanase and β-glucosidase, and enhanced the galactose metabolic pathway to utilize hemicellulose components. The resulting fermentable sugars were subsequently channeled through glycolysis and pyruvate metabolism pathways, with a notable upregulation of pyruvate kinase promoting the efficient conversion of pyruvate to LA. These findings provide valuable insights and a practical strategy for the efficient resource utilization of VW.