Amphibian skin microbiota exhibits temporal variation in community structure but stability of predicted Bd-inhibitory function

Host-associated microbiomes are increasingly recognized to contribute to host disease resistance; the temporal dynamics of their community structure and function, however, are poorly understood. We investigated the cutaneous bacterial communities of three newt species, Ichthyosaura alpestris, Lissotriton vulgaris and Triturus cristatus, at approximately weekly intervals for 3 months using 16S ribosomal RNA amplicon sequencing. We hypothesized cutaneous microbiota would vary across time, and that such variation would be linked to changes in predicted fungal-inhibitory function. We observed significant temporal variation within the aquatic phase, and also between aquatic and terrestrial phase newts. By keeping T. cristatus in mesocosms, we demonstrated that structural changes occurred similarly across individuals, highlighting the non-stochastic nature of the bacterial community succession. Temporal changes were mainly associated with fluctuations in relative abundance rather than full turnover of bacterial operational taxonomic units (OTUs). Newt skin microbe fluctuations were not correlated with that of pond microbiota; however, a portion of community variation was explained by environmental temperature. Using a database of amphibian skin bacteria that inhibit the pathogen Batrachochytrium dendrobatidis (Bd), we found that the proportion of reads associated with 'potentially' Bd-inhibitory OTUs did not vary temporally for two of three newt species, suggesting that protective function may be maintained despite temporal variation in community structure.