Internal and External Microbial Community of the Thitarodes Moth, the Host of Ophiocordyceps sinensis

Ophiocordyceps sinensis is a widely known medicinal entomogenous fungus, which parasitizes the soil-borne larva of Thitarodes (Hepialidae, Lepidoptera) distributed in the Qinghai–Tibetan Plateau and its adjacent areas. Previous research has involved artificial cultivation of Chinese cordyceps (the fungus-caterpillar complex), but it is difficult to achieve large-scale cultivation because the coupling relation between the crucial microbes and their hosts is not quite clear. To clarify the influence of the internal microbial community on the occurrence of Chinese cordyceps, in this study, the unfertilized eggs of Thitarodes of different sampling sites were chosen to analyze the bacterial and fungal communities via 16S rRNA and ITS sequencing for the first time. The results showed that for bacteria, 348 genera (dominant genera include Wolbachia, Spiroplasma, Carnobacterium, Sphingobium, and Acinetobacter) belonging to 26 phyla (dominant phyla include Proteobacteria, Firmicutes, Tenericutes, Actinobacteria, Acidobacteria, and Bacteroidetes), 58 classes, 84 orders, and 120 families were identified from 1294 operational taxonomic units (OTUs). The dominant bacterial genus (Spiroplasma) may be an important bacterial factor promoting the occurrence of Chinese cordyceps. For fungi, 289 genera, mainly including Aureobasidium, Candida, and Cryptococcus, were identified, and they belonged to 5 phyla (Ascomycota, Basidiomycota, Chytridiomycota, Glomeromycota, and Zygomycota), 26 classes, 82 orders, and 165 families. Eight bacterial OTUs and 12 fungal OTUs were shared among all of the detected samples and were considered as core species. Among them, Wolbachia, Spiroplasma, Carnobacterium, Aureobasidium, and Phoma may play important roles in helping the host larva to digest foods, adapt to extreme environments, or resist pathogens. On the other hand, the external (soil) microbial community was synchronously and comparatively analyzed. Comparative analysis revealed that external microbial factors might play a more significant role in the occurrence of Chinese cordyceps, owing to the significant differences revealed by α-diversity and β-diversity analyses among different groups. In summary, the results of this study may contribute to the large-scale cultivation of Chinese cordyceps.