【目的】为探究冬虫夏草菌Ophiocordyceps sinensis侵染小金蝠蛾Thitarodes xiaojinensis幼虫后肠道微生物菌群落演变规律，对优势菌群功能进行预测与评价，明确肠道微生物在冬虫夏草的形成过程中的营养供给机制。【方法】 选取健康未感菌的小金蝠蛾卵、1龄幼虫、5龄幼虫、蛹、成虫及感菌5龄幼虫的肠道组织进行16S rDNA检测，评价肠道内容物中的菌群功能及多样性差异。【结果】 在肠道组织内，菌群丰度随着龄期的增长逐渐降低，由1龄期的1 391种降低至蛹期的305种，肠道内的菌群以变形菌门（Proteobacteria）为优势菌群，只有少数为厚壁菌门（Fimicutes）。但是，在5龄幼虫感菌僵化的关键期内，肠道菌群生物丰富度、多样性和均匀度均有所降低。尤其是香浓指数（Shannon）、辛普森多样性指数（Simpson）及均匀度指数（Pielou’s evenness）与对照组存在显著差异（P=0.05），此时的优势菌群也更替为厚壁菌门，尤其是乳酸菌属（Lacticigenium）、肉食杆菌属（Carnobacterium）丰度显著上升。对比真菌侵染前后微生物代谢通路差异，发现视黄醇代谢、磷酸肌醇代谢、果糖和甘露糖代谢等消化相关通路均显著上调（P˂0.001），尤其是糖代谢途径中的丙酮酸发酵途径、磷酸戊糖途径、糖酵解途径分别上调8.44倍、4.19倍和2.90倍。通过对宿主消化能力进行验证，证实肠道消化功能显著提升，胰蛋白酶、蔗糖酶、脂肪酶活力分别提升（13 993±665.00）、（0.52±0.06）、（0.04±0.01）U/mL，尤其是淀粉酶酶活力相较于对照组差异极显著（P˂0.001），活力提升（0.68±0.01）U/mL。【结论】 冬虫夏草菌侵染宿主小金蝠蛾后，其肠道优势菌群更替为厚壁菌门，并参与多糖类代谢途径，提升肠道消化酶活力，促进宿主对营养物质的吸收利用。

[Objectives]  To investigate adaptative changes in the intestinal microbial community of Thitarodes xiaojinensis larvae following infection by Ophiocordyceps sinensis with the goal of predicting dominant microorganisms in infected individuals based on their function, and explain the nutrient supply mechanism underlying the increased abundance of certain microorganisms in cultivated Cordyceps sinensis. [Methods]  Healthy eggs and intestinal tissues from 1^st and 5^th instar larvae, pupae and adults, were selected for use as controls and intestinal tissues from mature 5^th instar larvae infected with Ophiocordyceps sinensis were collected for analyses. 16S rDNA sequencing was used to evaluate differences in microbial community structure and diversity between infected and non-infected intestinal contents. [Results]  In healthy intestinal tissues, bacterial abundance gradually decreased with age, from 1 391 species in first instar larvae, to 305 species in pupae. In healthy tissues, Proteobacteria were the dominant flora with only a few Firmicute species present. However, in infected larvae, the biological richness, diversity, and evenness of intestinal microorganisms decreased. The Shannon index, Simpson diversity index, and Pielou's evenness index of infected larvae were significantly different to those of the control group (P=0.05), and the Firmicutes were the dominant intestinal flora. Increases in Lactobacillus and Carnobacterium species were significant and pronounced. Analyses of microbial metabolic pathways after fungal infection revealed that energy metabolism pathways (retinol, inositol phosphate, fructose and mannose) were significantly up-regulated (P<0.001). Pyruvate fermentation, pentose phosphate, and glycolysis pathways were also up-regulated by 8.44-fold, 4.19-fold and 2.90-fold, respectively. Host digestive capacity was verified, confirming that intestinal digestive function was significantly improved. Trypsin, sucrase, and lipase increased by (13 993±665.00), (0.52±0.06) and (0.04±0.01) U/mL, respectively. The increase in amylase was especially significant; enzyme activity increased by (0.68±0.01) U/mL (P<0.001). [Conclusion]  O. sinensis infection changes the dominant intestinal flora of T. xiaojinensis from Proteobacteria to Firmicutes. Firmicutes participate in polysaccharide degradation, promoting nutrient absorption and utilization by the host.