Inhibition of Fungal Pathogens across Genotypes and Temperatures by Amphibian Skin Bacteria.

Symbiotic bacteria may dampen the impacts of infectious diseases on hosts by inhibiting pathogen growth. However, our understanding of the generality of pathogen inhibition by different bacterial taxa across pathogen genotypes and environmental conditions is limited. Bacterial inhibitory properties are of particular interest for the amphibian-killing fungal pathogens ( and ), for which probiotic applications as conservation strategies have been proposed. We quantified the inhibition strength of five putatively -inhibitory bacteria isolated from woodland salamander skin against six genotypes at two temperatures (12 and 18°C). We selected six genotypes from across the phylogeny: -Brazil and four genotypes of the Global Panzootic Lineage (GPL1: JEL647, JEL404; GPL2: SRS810, JEL423). We performed 96-well plate challenge assays in a full factorial design. We detected a genotype by temperature interaction on bacterial inhibition score for all bacteria, indicating that bacteria vary in ability to inhibit depending on pathogen genotype and temperature. moderately inhibited at both temperatures (μ = 46-53%), but not any genotypes. sp. inhibited three genotypes at both temperatures (μ = 5-71%). sp. strain 1 inhibited all genotypes at 12°C and four genotypes at 18°C (μ = 5-100%). sp. strain 2 and sp. moderately to strongly inhibited all six genotypes at both temperatures (μ = 57-100%). All bacteria consistently inhibited . Using cluster analysis of inhibition scores, we found that more closely related genotypes grouped together, suggesting that bacterial inhibition strength may be predictable based on relatedness. We conclude that bacterial inhibition capabilities change among bacterial strains, genotypes and temperatures. A comprehensive understanding of bacterial inhibitory function, across pathogen genotypes and temperatures, is needed to better predict the role of bacterial symbionts in amphibian disease ecology. For targeted conservation applications, we recommend using bacterial strains identified as strongly inhibitory as they are most likely to produce broad-spectrum antimicrobial agents at a range of temperatures.