Impact of contaminants on the interaction of chytrid fungus and anti-fungal bacteria

Background/Question/Methods   An important proposed strategy to dealing with the spread of the pathogenic fungus Batrachochytrium dendrobatidis (Bd) is the application of bacteria that produce chemicals toxic to Bd. Given the pervasiveness of chemical contaminants found in the environment, one important consideration is the impact that these contaminants might directly have on these protective bacteria. In addition, very little is known regarding the susceptibility of Bd to these chemicals. In this study, we examine the impacts of the herbicide glyphosate and the widely used antimicrobial compound triclosan on both Bd and the anti-Bd bacteria Pseudomonas fluorescens . Agar plates with concentrations of either glyphosate (0, 10, 100 µg/L) or triclosan (0, 1, 10, 100 µg/L) were used containing either bacteria, Bd, or the two combined. Growth of both bacteria and Bd were measured along with differences in the area of the zone of inhibition surrounding bacteria grown with Bd.

Results/Conclusions   Bacterial growth was significantly reduced in high glyphosate (100 µg/L) concentrations compared to controls. There was also a significant reduction in the zone of inhibition surrounding the bacteria at both low (10 µg/L) and high (100 µg/L) concentrations signifying a reduced effect of anti-fungal properties. Interestingly, the anti-microbial triclosan had no effect on either bacterial growth or fungal inhibition at any concentration. Although, triclosan high concentration plates (100 µg/L) exhibited fewer Bd zoosporangia. These results suggest the efficacy of anti-fungal bacteria can be reduced in the presence of low environmental concentrations of pesticides and that some contaminants might impact Bd directly. Future studies investigating impacts of prevalent contaminants on both bacteria and Bd might provide key insights into disease dynamics and in strategies dealing with the spread of Bd.