AUTHOR=Verbrugghe Elin , Adriaensen Connie , Martel An , Vanhaecke Lynn , Pasmans Frank 

TITLE=Growth Regulation in Amphibian Pathogenic Chytrid Fungi by the Quorum Sensing Metabolite Tryptophol

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.03277

DOI=10.3389/fmicb.2018.03277

ISSN=1664-302X

ABSTRACT=<p>Amphibians face many threats leading to declines and extinctions, but the chytrid fungal skin pathogens <italic>Batrachochytrium dendrobatidis</italic> (<italic>Bd</italic>) and <italic>Batrachochytrium salamandrivorans</italic> (<italic>Bsal</italic>) have been identified as the causative factors leading to one of the greatest disease-driven losses of amphibian biodiversity worldwide. Infection may lead to different clinical outcomes, and lethal infections are commonly associated with unrestricted, exponential fungal growth in the amphibian epidermis. Mechanisms underpinning <italic>Bd</italic> and <italic>Bsal</italic> growth in the amphibian host are poorly understood. Here, we describe a quorum sensing mechanism that allows cell-to-cell communication by <italic>Bd</italic> and <italic>Bsal</italic> in order to regulate fungal densities and infection strategies. Addition of chytrid culture supernatant to chytrid cultures resulted in a concentration-dependent growth reduction and using dialysis, small metabolites were shown to be the causative factor. U-HPLC-MS/MS and <italic>in vitro</italic> growth tests identified the aromatic alcohol tryptophol as a key metabolite in regulating fungal growth. We determined tryptophol kinetics in both <italic>Bd</italic> and <italic>Bsal</italic> and confirmed the autostimulatory mode of action of this quorum sensing metabolite. Finally, we linked expression of genes that might be involved in tryptophol production, with <italic>in vitro</italic> and <italic>in vivo</italic> chytrid growth. Our results show that <italic>Bd</italic> and <italic>Bsal</italic> fungi use tryptophol to act as multicellular entities in order to regulate their growth.</p>