Microsporidia

Abstract

Microsporidia are unicellular, obligate intracellular, spore-forming eukaryotes classified among the protists. As parasites, they have been reported from every major group of animals from other protists to mammals and man. They are economically and medically important and can be found environmentally in terrestrial, marine, and freshwater ecosystems. This phylum consists of over 200 genera and approximately 1,300 species producing benign to lethal infec- tions. While they are extremely diverse, they all share the diagnostic and unique resistant spore. It contains a polar filament complex which begins the life cycle by extruding this filament injecting the spore contents, the sporoplasm, into a host cell. As intracellular parasites, they are dependent upon their host for access to nutritional products and have evolved several ways to obtain the required metab- olites which in turn have reduced their need to produce many of the biochemicals necessary for their development. As a result of this reduced need to produce their own metabolites, there has been a reduction in their physiological machinery, as well as formation of unique organelles and biochemical pathways. Gene sequenc- ing data has indicated diversity in genome size that ranges from 50+Mbp to the smallest eukaryotic genome reported to date (2.3 Mbp).