SMALL-SUBUNIT RIBOSOMAL DNA PHYLOGENY OF VARIOUS MICROSPORIDIA WITH EMPHASIS ON AIDS-RELATED FORMS

Phylogenetic analysis of the small subunit ribosomal DNA of a broad ra nge of representative microsporidia including five species from humans (Enterocytozoon bieneusi, Nosema corneum, Septata intestinalis, Encep halitozoon hellem and Encephalitozoon cuniculi), reveals that human mi crosporidia are polyphyletic in origin. Septata intestinalis and E. he llem are very similar to the mammalian parasite E. cuniculi Based on t he results of our phylogenetic analysis, we suggest that S. intestinal is be designated Encephalitozoon intestinalis. Furthermore, analysis o f our data indicates that N. corneum is much more closely related to t he insect parasite Endoreticulatus schubergi than it is to other Nosem a species. This finding is supported by recent studies which have show n a similarity between E. schubergi and N. corneum based on the origin and development of the parasitophorous vacuole. Thus these opportunis tic microsporidian parasites can originate from hosts closely or dista ntly related to humans. Finally, the phylogeny based on small subunit ribosomal DNA sequences is highly inconsistent with traditional classi fications based on morphological characters. Many of the important mor phological characters (diplokaryon, sporophorous vesicle, and meiosis) appear to have multiple origins.