Descriptions

Outline

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Batrachochytrium dendrobatidis

Batrachochytriumis a pathogen of amphibians implicated as a primary causative agent of amphibian declines (1,2). This recently emerging pathogen was identified in 1998 as the cause of amphibian deaths in Australia and Central America (3). More recently, Batrachochytrium dendrobatidis has been implicated in population declines of frog species in North America, South America, Europe and Africa. This fungus invades the top layers of skin cells and causes thickening of the keratinized layer (3,4). Because amphibians drink and breathe through their skin, the fungus may kill them by disrupting these mechanisms. Alternatively, the fungus may be secreting a toxin.

As a representative of the Chytridiomycota (chytrids), the sequence of B. dendrobatidis is the first in this largely uncharacterized phylum of fungi. Batrachochytrium is a non-filamentous (monocentric) chytrid firmly within the order Rhizophydiales, based on ultrastructural characteristics and molecular sequence data; the Rhizophydiales is a new order recently segregated from the polyphyletic Chytridiales (5).

As members of both aquatic and terrestrial microbial communities, chytrids are parasites and saprobes of many microscopic organisms (e.g. pollen, algae, and invertebrates) and play an important ecological role in the degradation of recalcitrant materials, such as chitin, keratin, and cellulose. Chytrids are unique among the true fungi in possessing zoospores, which move using flagella (6). Phylogenetic studies based on rDNA and on whole mitochondrial genome sequences indicate that the chytrids are basal in the fungal clade (3,7). This basal position increases the value of a whole genome sequence for comparative genomics within the fungal clade and also with the sister animal clade.