Karst caves are distinctly characterised by darkness, low to moderate temperatures, high humidity, and scarcity of organic matter. During the years of 2014–2015, we explored the mycobiota in two unnamed Karst caves in Guizhou province, China, and obtained 563 fungal strains via the dilution plate method. Preliminary ITS analyses of these strains suggested that they belonged to 246 species in 116 genera, while 23.5 % were not identified to species level. Among these species, 85.8 % (211 species) belonged to Ascomycota; 7.3 % (18 species) belonged to Basidiomycota; 6.9 % (17 species) belonged to Mucoromycotina. The majority of these species have been previously known from other environments, mostly from plants or animals as pathogens, endophytes or via a mycorrhizal association. We also found that 59 % of these species were discovered for the first time from Karst caves, including 20 new species that are described in this paper. The phylogenetic tree based on LSU sequences revealed 20 new species were distributed in six different orders. In addition, ITS or multi-locus sequences were employed to infer the phylogenetic relationships of new taxa with closely related allies. We conclude that Karst caves encompass a high fungal diversity, including a number of previously unknown species. Novel species described include: Amphichorda guana, Auxarthronopsis guizhouensis, Biscogniauxia petrensis, Cladorrhinum globisporum, Collariella quadrum, Gymnoascus exasperatus, Humicola limonisporum, Metapochonia variabilis, Microascus anfractus, Microascus globulosus, Microdochium chrysanthemoides, Paracremonium variiforme, Pectinotrichum chinense, Phaeosphaeria fusispora, Ramophialophora globispora, Ramophialophora petraea, Scopulariopsis crassa, Simplicillium calcicola, Volutella aeria, and Wardomycopsis longicatenata.

Caves are typified by their permanent darkness and a shortage of nutrients. Consequently, bacteria play an important role in sustaining such subsurface ecosystems by dominating primary production and fueling biogeochemical cycles. China has one of the world’s largest areas of karst topography in the Yunnan-Guizhou Plateau, yet the bacteriomes in these karst caves remain unexplored. In this study, bacteriomes of eight karst caves in southwest China were examined, and co-occurrence networks of cave bacterial communities were constructed. Results revealed abundant and diversified bacterial communities in karst caves, with Proteobacteria , Actinobacteria , and Firmicutes being the most abundant phyla. Statistical analysis revealed no significant difference in bacteriomes among the eight caves. However, a PCoA plot did show that the bacterial communities of 128 cave samples clustered into groups corresponding to sampling types (air, water, rock, and sediment). These results suggest that the distribution of bacterial communities is driven more by sample types than the separate caves from which samples were collected. Further community-level composition analysis indicated that Proteobacteria were most dominant in water and air samples, while Actinobacteria dominated the sediment and rock samples. Co-occurrence analysis revealed highly modularized assembly patterns of the cave bacterial community, with Nitrosococcaceae wb1-P19, an uncultured group in Rokubacteriales , and an uncultured group in Gaiellales , being the top-three keystone members. These results not only expand our understanding of cave bacteriomes but also inspires functional exploration of bacterial strains in karst caves.

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