# Double-edged effects of aquatic environmental biofilms on Batrachochytrium dendrobatidis growth and inhibition

## TL;DR

Aquatic biofilms both support and inhibit the growth of a deadly amphibian fungus, suggesting new ways to control its spread.

## Contribution

The study reveals the dual role of aquatic biofilms in promoting and inhibiting Bd growth through microbial interactions.

## Key findings

- Aquatic biofilms allow Bd to complete its life cycle briefly in the absence of amphibian hosts.
- Exposure to biofilms or planktonic microorganisms significantly reduces Bd DNA within a week.
- Nutrient addition enhances the inhibitory effect of aquatic microbiota on Bd.

## Abstract

Batrachochytrium dendrobatidis (Bd) is an aquatic chytrid fungus that infects amphibians and has the potential to remain viable outside of hosts. However, the role of aquatic microbiota in influencing Bd growth and survival remains insufficiently understood. In this study, we demonstrated that in the absence of amphibian hosts, aquatic environmental (AE) biofilms supported the development of Bd, allowing it to complete its life cycle for a short period; whereas aquatic planktonic microorganisms did not. However, exposure of Bd zoospores to AE biofilms or planktonic microorganisms resulted in a significant reduction in Bd DNA within a week. These results suggest a dual role of aquatic biofilms in both supporting Bd growth and inhibiting it simultaneously. Moreover, Bd monolayers, composed mainly of zoosporangia, rapidly declined when exposed to AE planktonic microorganisms. Laboratory-formulated nutrients further enhanced the Bd-inhibitory effect of AE microbiota, suggesting that competition for shared nutrients plays a role in this interaction. This study advances our understanding of the complex interactions between Bd and aquatic microbial communities, underscores the ecological significance of biofilm-associated environments, and supports the potential of microbiota-informed interventions for controlling chytridiomycosis in amphibians.