Amphibian Symbiotic Bacteria Do Not Show a Universal Ability To Inhibit Growth of the Global Panzootic Lineage of Batrachochytrium dendrobatidis

Abstract

Microbiomes associated with multicellular organisms influence the disease susceptibility of hosts. The potential exists for such bacteria to protect wildlife from infectious diseases, particularly in the case of the globally distributed and highly virulent fungal pathogen Batrachochytrium dendrobatidis of the global panzootic lineage (B. dendrobatidis GPL), responsible for mass extinctions and population declines of amphibians. B. dendrobatidis GPL exhibits wide genotypic and virulence variation, and the ability of candidate probiotics to restrict growth across B. dendrobatidis isolates has not previously been considered. Here we show that only a small proportion of candidate probiotics exhibited broad-spectrum inhibition across B. dendrobatidis GPL isolates. Moreover, some bacterial genera showed significantly greater inhibition than others, but overall, genus and species were not particularly reliable predictors of inhibitory capabilities. These findings indicate that bacterial consortia are likely to offer a more stable and effective approach to probiotics, particularly if related bacteria are selected from genera with greater antimicrobial capabilities. Together these results highlight a complex interaction between pathogens and host-associated symbiotic bacteria that will require consideration in the development of bacterial probiotics for wildlife conservation. Future efforts to construct protective microbiomes should incorporate bacteria that exhibit broad-spectrum inhibition of B. dendrobatidis GPL isolates.

FIG 1

Average (±1 SEM) inhibition scores for 15 bacteria from quantitative in vitro challenges against three B. dendrobatidis GPL (BdGPL) isolates. *, within each bacterium, B. dendrobatidis isolates with inhibition scores significantly different from those for B. dendrobatidis isolates without an asterisk.

FIG 2

Average (±1 SEM) inhibition scores for multiple bacteria from four genera used to challenge three B. dendrobatidis GPL isolates. Inhibition scores against VA05 isolates were significantly lower than those against the other B. dendrobatidis GPL isolates (*), and Enterobacter spp. showed a significantly lower inhibition of the range of B. dendrobatidis GPL isolates than the other bacteria (#).