Culture-dependent and -independent analyses reveal unique community structure and function in the external mycelial cortices of Ophiocordyceps sinensis.

Ophiocordyceps sinensis, also known as DongChong XiaCao (DCXC) in China, is a complex of the parasitic fungus Hirsutella sinensis and its caterpillars host living in extreme alpine environments on the Qinghai-Tibetan Plateau. Wild resources of O. sinensis are threatened by over-harvesting due to its perceived high medicinal value. In recent years, numerous studies have pointed out that endofungal bacteria play an important role in fungal spore germination and zygote formation. In this sense, studying the endofungal bacteria of O. sinensis is of great interest regarding the conservation of this species. In this study, we investigated the community structure (abundance and rare sub-communities) and function of the soil-mycelial-sclerotia-stromata continuum endofungal bacteria in O. sinensis from the Qilian Mountain region of the Tibetan Plateau by using amplicon and macro-genome sequencing technologies. Based on the results, rare taxa exhibited more differences among the components, and enrichment and co-occurrence network analyses revealed that abundant taxa played a more important role. We further found that endofungal bacteria in external mycelial cortices have unique community structures and functions. In particular, they play an important role in material cycling, potentially providing essential nutrients during the lifecycle of O. sinensis. We successfully isolated 52 endofungal bacterial strains using high-throughput isolation techniques, some of them were undetected by high-throughput sequencing. We systematically investigated the structure and function of endofungal bacteria of the O. sinensis, providing a solid foundation for the cultivation and conservation of wild resources of this species at an industrial scale.