Abstract:[Objective] To elucidate the structural and functional characteristics of the gut microbiota of Trypoxylus dichotomus larvae and isolate cellulose-degrading bacteria. [Methods] Metagenomic sequencing was employed to analyze the structure and functions of the gut microbiota. Cellulose-degrading bacteria were isolated and screened from the larval gut with carboxymethyl cellulose (CMC) as the sole carbon source. The strains were identified based on morphological characteristics and molecular evidence. [Results] The gut microbiota was dominated by bacteria, which accounted for 81.3%. At the phylum level, Firmicutes (45.8%) and Bacteroidota (20.3%) were the dominant phyla. The top three abundant genera were Clostridium (3.90%), Bacteroidia (3.52%), and Dysgonomonas (2.41%). The functional analysis of metagenome data revealed that the genes of the gut microbiota were mainly associated with carbohydrate, amino acid, and energy metabolism. The annotation in the Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed that the genes related to carbohydrate metabolism were predominant. The annotation in the carbohydrate-active enzyme database (CAZy) indicated that 48 856 (7.43%) genes were successfully annotated to 344 carbohydrate metabolism enzyme families, with glycoside hydrolase (GH, 48.67%) being the most dominant enzyme family in the gut bacteria. Among the top ten functionally abundant enzymes, six belonged to the GH family. Additionally, three strains of cellulose-degrading bacteria, TRC-3 (Bacillus subtilis), TRC-5 (B. subtilis), and TRC-6 (B. safensis), were isolated from the gut. TRC-3 exhibited stronger activities of filter paper enzyme, endoglucanase, exoglucanase, and β-glucosidase. [Conclusion] The gut microbiota of Trypoxylus dichotomus larvae exhibits high diversity and complexity, carrying a large number of genes encoding carbohydrate-active enzymes and harboring rich cellulose-degrading bacteria.
