Seasonal changes and the unexpected impact of environmental disturbance on skin bacteria of individual amphibians in a natural habitat.

Amphibians host diverse skin bacteria that have a role in pathogen defense, but these skin communities could change over time and impact this function. Here, we monitored individual Eastern red-spotted newts (Notophthalmus viridescens; N = 17) for 2 years in a field pond enclosure and assessed the effects of season and disturbance on skin bacterial community dynamics. We created disturbances by adding additional pond substrate to the enclosure at two timepoints. We planned to sample the skin bacterial community and metabolite profiles of each newt every 6 weeks; we ultimately sampled eight individuals at least six times. We used 16S rRNA gene amplicon sequencing to characterize the bacterial communities and HPLC-MS for metabolite profiling. We found that disturbance had a dramatic effect on skin bacterial communities and metabolite profiles, while season had an effect only using select metrics. There were seven core bacterial taxa (97% OTUs) that were found on all newts in all seasons, pre- and post-disturbance. Lastly, there was a correlation between bacterial and metabolite profiles post-disturbance, which was not observed pre-disturbance. This longitudinal study suggests that environmental disturbances can have lasting effects on skin bacterial communities that overwhelm seasonal changes, although the core bacteria remain relatively consistent over time.