Environmental factors and host sex influence the skin microbiome structure of Hong Kong newt (Paramesotriton hongkongensis) in a coldspot of chytridiomycosis in subtropical East Asia

Chytridiomycosis, an infectious skin disease caused by the chytrid fungi, Batrachochytrium dendrobatidis and B. salamandrivorans, has been threatening global amphibian biodiversity. On the skin of chytrid-resistant amphibians, some antifungal bacteria likely defend them against chytridiomycosis, reducing the mortality of resistant amphibians. The Hong Kong newt (Paramesotriton hongkongensis) inhabits East Asia which is a suspected origin of chytrids. Asymptomatic infection in the newts suggests their long-term coexistence with chytrids. Thus, the skin microbiomes of this resistant species warrant investigation, along with other factors that can affect the microbiome. Among the 149 newts sampled in their natural habitats in Hong Kong, putative antifungal bacteria were found on all newts. There were 314 amplicon sequence variants distributed over 25 genera of putative antifungal bacteria, abundant ones included Acinetobacter, Flavobacterium, and Novosphingobium spp. The skin microbiome compositions were strongly influenced by the inter-site geographical distances. Despite inter-site differences, we identified some core skin microbes across sites, which could be vital to P. hongkongensis. The dominant cores included family Comamonadaceae, family Chitinophagaceae, and class Betaproteobacteria. Moreover, habitat elevation and host sex also exhibited significant effects on skin microbiome compositions. The antifungal bacteria found on these newts offer an important resource for conservation against chytridiomycosis, such as probiotic treatments for susceptible species.