A novel bioaugmentation technique effectively increases the skin-associated microbial diversity of captive eastern hellbenders

Captive environments are maintained in hygienic ways to prevent the spread of disease, but can also lack natural microbial reservoirs. As a result, captive animals often have depauperate host-associated microbial communities compared to conspecifics in the wild and may have increased disease susceptibility and reduced immune function. Eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) are reared in captivity before being translocated to the wild. To prepare hellbenders for natural bacteria found in riverine environments, we devised a novel bioaugmentation method to increase the diversity of skin microbial communities within a captive setting. We exposed three-year-old hellbenders to increasing amounts of river water over five weeks before translocating them to the river. We genetically identified and phylogenetically compared bacteria collected from skin swabs and river water for alpha (species richness) and beta (community composition) diversity estimates. We found that hellbenders exposed to undiluted river water in captivity had higher alpha diversity and distinct differentiation in the community composition on their skin, compared to hellbenders only exposed to well water. We also found strong evidence that hellbender skin microbiota is host specific rather than environmentally driven and is colonized by rare environmental operational taxonomic units (OTUs) in river water. This novel technique may be beneficial for future translocation efforts as increasing microbial diversity is often correlated with elevated disease resistance. Future work is necessary to refine our methods, investigate the relationship between microbial diversity and hellbender health, and understand how this novel bioaugmentation technique influences hellbenders’ survival following translocation from captivity into the wild.