Abstract: 【Aim】To reveal the community composition and functional characteristics of the symbiotic microbes in Ips nitidus. 【Methods】Metagenomics and correlation network analysis were conducted on the symbiotic fungi and bacteria in the gut and other tissues of I. nitidus from Maixiu Nature Reserve in Qinghai Province, Northwest China to compare the community composition of the symbiotic fungi and bacteria in the gut and other tissues of I. nitidus, to analyze the interrelationships of the microbial communities and to annotate the functional genes of the symbiotic microbes by non-redundant protein sequence alignment method. 【Results】A total of 3 520 species of symbiotic microbes were found in the gut and other tissues of I. nitidus. Fungi and bacteria possessed the highest numbers of species (accounting for 23.21% and 69.01% of all species, respectively), with the average relative abundance of 9.69% and 13.79%, respectively. For fungal symbionts, Erysiphales showed higher relative abundance and species diversity in other tissues than in the gut, and Saccharomycetales showed lower relative abundance and species diversity in other tissues than in the gut. Ophiostomatoid fungi in other tissues showed higher species diversity than those in the gut (16 species of 6 genera, and 13 species of 5 genera, respectively). The average relative abundance of ophiostomatoid fungi in other tissues and gut occupied 0.016% and 0.013%, respectively. The relative abundance and species diversity of Enterobacterales in other tissues were higher than those in the gut. Enterobacter, Erysiphe, Rhizophagus and Wolbachia were the core genera in the gut and other tissues. Some communities of fungi and bacteria showed opposite interrelationships in the gut and other tissues, suggesting that there may be complex interactions between the symbionts in I. nitidus. A total of 7 010 and 6 483 functional genes were identified from symbiotic fungi and bacteria, respectively. The number of functional genes related to xenobiotics biodegradation and metabolism in bacteria was higher than that in fungi. However, 11 pathways such as mRNA surveillance pathway, propanoate metabolism, ubiquitin-mediated proteolysis and so on had more significant differential genes in the gut than in other tissues. The annotation results for functional genes related to limonene degradation and sterol synthesis showed that bacteria may degrade limonene significantly compared with fungi, but fungi may play a more crucial role in promoting sterol biosynthesis than bacteria. A total of 74 functional genes of ophiostomatoid fungi are mainly involved in oxidative phosphorylation, metabolic pathway and amino acid metabolism. Moreover, ophiostomatoid fungi were of higher diversity in other tissues and mainly distributed in Ophiostoma, etc. 【Conclusion】There are some differences in the community composition, diversity and function of the symbiotic microbes in the gut and other tissues of I. nitidus. Enterobacter, Erysiphe, Rhizophagus and Wolbachia are the most important core flora, and they might play an important role in the community assembly.

Key words: Ips nitidus, symbionts, functional gene, interaction, terpenoid degradation, ophiostomatoid fungi