Effects of Solid-State Fermentation with Compound Bacterial Inoculant on the Nutritional Quality, Microbial Community Structure, and Metabolic Profile of Ziziphus mauritiana Straw

This study investigated the effects of solid-state fermentation with a compound microbial inoculant on the nutritional composition, microbial community structure, and metabolic products of green jujube (Ziziphus mauritiana Lam.) straw. The results demonstrated that solid-state fermentation significantly enhanced the nutritional value of the straw, as evidenced by a marked increase in crude protein content and significant reductions in neutral detergent fiber (NDF), acid detergent fiber (ADF), and cellulose content. Metagenomic analysis revealed that fermentation substantially altered the microbial community structure of the straw, with a pronounced increase in the relative abundance of bacteria from the phylum Pseudomonadota (particularly genera such as Klebsiella and Enterobacter), and an upward trend in the abundance of fungi from the phylum Basidiomycota (Astraeus). Functional annotation indicated that fermentation enhanced the potential of the straw microbiota in genetic information processing, ABC transporters, and starch and sucrose metabolism, while attenuating the oxidative phosphorylation pathway. Metabolomic analysis identified 1176 differential metabolites, with significant increases in bioactive compounds such as peptides, amino acids, polyunsaturated fatty acids, and flavonoids following fermentation. Correlation analysis further revealed significant associations between specific microorganisms (Klebsiella, Enterobacter, and Aureobasidium) and key metabolites (amino acids, peptides, and flavonoids) in the fermented green jujube straw. This study confirms that solid-state fermentation can effectively improve the nutritional value and functional properties of the agricultural by-product green jujube straw by reshaping its microbial ecosystem and metabolic network.