Two-phase sequential solid-state fermentation based on a synthetic microbial community enhances short-chain fatty acid production from sugarcane dry leaves

Sugarcane dry leaves (SDL) are underutilized in feed and food industries due to their dense lignocellulose and low digestibility, requiring bioconversion. Trichoderma erinaceum , secreting efficient cellulases, is a promising degrader, but traditional fermentation is prone to variability and contamination, while single strains are metabolically limited. Therefore, we introduced a synthetic microbial community and developed a two-phase sequential fermentation: aerobic phase with Trichoderma erinaceum for 5 days to hydrolyze cellulose, followed by anaerobic phase with Kluyveromyces marxianus , Lactiplantibacillus plantarum and Limosilactobacillus fermentum for 5 days to accumulate organic acids. After aerobic phase, group A (two-phase aerobic-anaerobic fermentation with consortium) reduced neutral detergent fiber (DM basis) by 3.91% and acid detergent fiber (DM basis) by 4.59% vs. control (CK). After anaerobic phase, crude protein increased by 10.49%, lactic acid (LA) by 18.65%, and acetic acid (AA) by 291.09% in group A. Metagenomics revealed that elevated LA during the aerobic phase coincided with K. marxianus enrichment, while LA/AA accumulation during the anaerobic phase accompanied Lentilactobacillus enrichment, and GH enrichment correlated with fiber degradation. Untargeted metabolomics revealed 3264 differential metabolites, including upregulated zosteric acid, 3-hydroxycinnamic acid, cyclo(Pro-Arg), and carquinostatin A, which were associated with antimicrobial, flavor, antioxidant and were positively correlated with Lentilactobacillus ; 4-aminobutanoate accumulation was correlated with enhanced acid tolerance of Lentilactobacillus , thus indirectly promoting LA and AA production. Overall, this two-phase sequential solid-state fermentation combined with a synthetic microbial community effectively converts SDL into organic acid-rich biomass, offering a viable route for high-value feed and functional food ingredients within a circular bioeconomy.