A novel sustainable and microbial functional modulation strategy for directly transforming corn straw into high-value...

The natural hydrolysis-acidification (HA) process of straw for medium-chain fatty acid (MCFA) synthesis often faces insufficient selectivity and poor control over the production of lactic acid (LAc) and acetic acid (HAc). Restructuring the microbial community can help regulate the production of LAc and HAc. This study established a fully modularized, resource-recycling system for MCFA production by the targeted enrichment of LAc and HAc functional species. First, within the 20 days of silage, corn straw was rapidly converted to LAc and HAc, with Lactobacillus and Acetobacter being remarkably enriched to 10¹⁰ copies/g VS. Subsequently, the HA module was optimized with a solid content of 10 % and an initial acidic pH of 5.5, which increased the hemicellulose degradation rate from 6.38 % to 17.24 %. While maintaining the HAc concentration, the LAc levels rose from 2.8 g/L to 4.6 g/L, and butyric acid production was suppressed. A predictive model for the caproic acid production, based on LAc and HAc was established and achieved an R² value of 0.97. Lactobacillus dominated the system, while Acetobacter in the feedstock was gradually replaced by Clostridium, whose abundance increased from 13.87 % to 41.30 %. Syntrophobacter, Syner-01 enhanced the potential for pyruvate metabolism, a key metabolic pathway hub of LAc-HAc production. Key species predicted by random forest analysis were also enriched in reality, which revealed the regulatory mechanism of HA product formation. Furthermore, a life cycle assessment (LCA) demonstrated the environmental and economic advantages of the modularity of our production line, which provides a high-value solution for straw anaerobic digestion.