Professor Fordham University Bronx, New York, United States
Priority effects, in which the order of species’ arrival influences their interactions, have been observed to play a key role in the assembly of macro- and microorganisms. In host-associated microbiomes, priority effects can influence not only community composition and structure, but also functions such as disease resistance. This study explores the role of priority effects in determining community composition and function using the amphibian skin microbiome as a model system. Scientists have found that amphibian protection from chytridiomycosis (caused by the invasive fungal pathogen, Batrachochytrium dendrobatidis (Bd)) is directly related to native bacterial composition on host skin. Because the skin is a highly exposed environment (as compared to internal host environments), community composition is largely impacted by stochastic loss or acquisition of microbes explaining why individuals within a population can vary in their susceptibility to pathogens. We used a 3 x 3 x 4 factorial design with three orders of Bd introduction, three combinations of bacterial species, and four timepoints. We tracked microbial abundance using qPCR and estimated pathogen inhibition by challenging naive cultures of Bd with metabolites produced during bacteria-Bd co-culture.
We demonstrate that priority effects can influence interactions among amphibian-associated bacteria and Bd. We observed strong priority effects irrespective of high anti-fungal ability: Bd exerted an inhibitory effect on highly anti-fungal bacteria and facilitative effect on weakly anti-fungal bacteria. Additionally, we found that the Bd-inhibitory potential of a co-culture of two strongly inhibitory bacterial species did not work additively or synergistically to produce higher levels of Bd-inhibition than either species alone. Together, these results suggest that priority effects between commensal and pathogenic taxa can be either inhibitory or facilitative, with the strength and direction of this effect dependent on community composition. Thus, changes in assembly order may lead to varying levels of Bd infection, influencing the success of amphibian microbiome bioaugmentation for conservation.