Batrachochytrium dendrobatidis is a fungal pathogen of amphibians that is increasingly implicated as a major cause of large-scale mortalities of amphibian species worldwide. Previous studies indicate that motile zoospores of B. dendrobatidis colonize the keratinized tissues of susceptible amphibians. Infections spread to adults and cause destruction of epidermal tissue. In an effort to understand how the chytrid cues into its host we developed an assay to study chemotaxis in the fungus. Here we show that zoospores exhibit positive movement toward a variety of attractants including sugars, proteins and amino acids. These observations suggest that the chytrid can respond to nutritional cues, including those of host origin. Implications of these observations to amphibian susceptibility to infection and chytrid virulence are discussed.

Batrachochytrium dendrobatidis (Bd) has been identified as a causative agent in the precipitous decline of amphibians worldwide. Studies on the fungus including its ability to infect and kill the host require use of frogs, a precious resource. Therefore, the development of an alternate host model to study the virulence of the fungus would be useful. Here, we show that Bd can cause mortality in the nematode Caenorhabditis elegans. Incubation of Bd with C. elegans resulted in greater than 70% mortality in the nematodes over a period of 24 h. Fluorescence microscopy using propidium iodide, a fluorescent dye used to determine cell viability, and tactile assays were used to discriminate between live and dead nematodes. These observations suggest that C. elegans may be a useful model organism to study the pathogenicity and virulence mechanisms of Bd.

Batrachochytrium dendrobatidis is a fungal pathogen of amphibians that is increasingly implicated as a major cause of large-scale mortalities of amphibian species worldwide. Previous studies indicate that motile zoospores of B. dendrobatidis colonize the keratinized tissues of susceptible amphibians. Infections spread to adults and cause destruction of epidermal tissue. In an effort to understand how the chytrid cues into its host we developed an assay to study chemotaxis in the fungus. Here we show that zoospores exhibit positive movement toward a variety of attractants including sugars, proteins and amino acids. These observations suggest that the chytrid can respond to nutritional cues, including those of host origin. Implications of these observations to amphibian susceptibility to infection and chytrid virulence are discussed.

Batrachochytrium dendrobatidis (Bd) is a fungus that causes chytridiomycosis, a disease that has been implicated as a cause of amphibian population declines worldwide. Infected animals experience hyperkeratosis and sloughing of the epidermis due to penetration of the keratinized tissues by the fungus. These symptoms have led us to postulate that Bd produces proteases that play a role in the infection process. Here, we show that Bd is capable of degrading elastin in vitro, a protein found in the extracellular matrix of the host animal. Elastolytic enzyme activity was partially purified using ion exchange chromatography and size-exclusion filtration from cultures grown in inducing media. The elastolytic activity of the purified fraction had a pH optimum of 8, was strongly inhibited by EDTA and phenylmethylsulfonyl fluoride (PMSF), and was partially inhibited by an elastasespecific inhibitor. This activity was also enhanced by the presence of Mg 2+ and Ca 2+ but not Zn 2+. An antiserum directed against Aspergillus fumigatus serine protease (Alp) was found to react with a polypeptide of approximately 110 kDa from the purified material. Using immunofluorescence, this antiserum was also observed to react with zoospores and sporangia grown on toad skin. These observations suggest that Bd may produce proteases similar to those produced by other pathogenic fungi that are capable of degrading proteins found in the extracellular matrix. The proteolytic activity exhibited in vitro might aid the organism in its ability to colonize and destroy the epidermis of its amphibian host.