Batrachochytrium dendrobatidis

Batrachochytrium dendrobatidis is a chytrid fungus that causes the amphibian disease chytridiomycosis.

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Systematics

It is the only known species of the genus Batrachochytrium. The initial classification of the pathogen as a Chytrid was based on zoospore ultrastructure. DNA analysis of the ssu-rDNA has corroborated the view, with the closest match to Chytridium confervae.

Morphology

The fungus in the epidermis has a thallus bearing a network of rhizoids and smooth-walled, spherical to subspherical, inoperculate sporangia. Each sporangium produces a single discharge tube. Zoospores have an elongate–ovoidal body and a single, posterior flagellum and possess a core area of ribosomes often with membrane-bound spheres of ribosomes within the main ribosomal mass. A small spur has been observed, located at the posterior of the cell body, adjacent to the flagellum, but this may be an artifact in the formalin-fixed specimens. The core area of ribosomes is surrounded by a single cisterna of endoplasmic reticulum, two to three mitochondria, and an extensive microbody–lipid globule complex. The microbody closely appose and almost surround four to six lipid globules (three anterior and one to three laterally), some of which appear bound by a cisterna. Some zoospores appear to contain more lipid globules (this may have been a result of a plane-of-sectioning effect, because the globules were often lobed in the zoospores examined). A rumposome has not been observed. A nonfunctioning centriole lay adjacent to the kinetosome. Nine interconnected props attach the kinetosome to the plasmalemma, and a terminal plate is present in the transitional zone. An inner ring-like structure attached to the tubules of the flagellar doublets within the transitional zone has been observed in transverse section. No roots associated with the kinetosome have been observed. In many zoospores, the nucleus lay partially within the aggregation of ribosomes and was invariably situated laterally. Small vacuoles and a Golgi body with stacked cisternae occurred within the cytoplasm outside the ribosomal area. Mitochondria, which often contain a small number of ribosomes, are densely staining with discoidal cristae.

Life cycle

Batrachochytrium dendrobatidis has two life stages - a sessile, reproductive zoosporangium and a motile, uniflagellated zoospore released from the zoosporangium.

References

• Chytridiomycosis causes amphibian mortality associated with population declines in the rain forests of Australia and Central America[1]
• Emerging Infectious Diseases and Amphibian Population Declines[2]
• Survival of Batrachochytrium dendrobatidis in Water: Quarantine and Disease Control Implications[3]
• Systematics [4]