Submitted to: International Coloquim on Invertebrate Pathology and Microbial Control
Publication Type: Proceedings
Publication Acceptance Date: April 30, 2002
Publication Date: August 15, 2002
Citation: HUMBER, R.A. MICROSPORIDIAN ROOTS AND BRANCHES WITHIN THE ZYGOMYCOTA? TAKE A NUMBER AND STAND IN LINE!. INTERNATIONAL COLOQUIM ON INVERTEBRATE PATHOLOGY AND MICROBIAL CONTROL. 2002. Technical Abstract: Molecular systematics techniques have proven that the Microsporidia, a large and important group of intracellular parasites affecting mostly insects, is related to zygomycete fungi. Microsporidia, which have no mitochondria in their cells, have long been thought to be evolutionarily primitive protozoans. The discovery that microsporidians have become ever simpler over time, losing their mitochondria (a cell's 'power plants') and becoming physiologically dependent on their host cells support is a major break from previous beliefs. The evolutionary link between the microsporidia and fungi appears to be with some of the simpler fungi in the phylum Zygomycota although differing studies have suggested close relationships with at least two zygomycete groups. The Zygomycota, as traditionally understood, is an evolutionarily diverse group of fungi among which evolutionary relationships remain poorly understood. This paper presents some current ideas about relationships within the zygomycete fungi and draws on basic biological information about those fungi with which molecular genetic evidence suggests microsporidia are most closely related, particularly the Trichomycetes and Entomophthorales. Trichomycetes are found almost exclusively on the linings of arthropod guts and survive mainly on nutrients passing through the host's gut. The Entomophthorales (which may comprise fungi from at least two different evolutionary backgrounds) are best known as arthropod pathogens but their ancestors used nonliving food sources) rather than as pathogens. To go beyond the limited molecular data to find the larger correspondences, similarities and differences between microsporidians and the fungi is a major challenge that is also the source of controversy and a continuing dialog among a diverse set of biologists seeking the answers.