RIBOSOMAL DNA-SEQUENCES OF ENCEPHALITOZOON-HELLEM AND ENCEPHALITOZOON-CUNICULI - SPECIES IDENTIFICATION AND PHYLOGENETIC CONSTRUCTION

A segment of ribosomal DNA, about 1,350 base pairs long, was amplified from the microsporidian species Encephalitozoon hellem, isolated from AIDS patients, and Encephalitozoon cuniculi. The amplified DNA segmen t extends from position 530 in the small ribosomal RNA subunit to posi tion 580 in the large ribosomal RNA subunit. A comparison of sequence data from this region for Encephalitozoon hellem and Encephalitozoon c uniculi shows relatively high sequence similarity, supporting the plac ement of these two organisms in the same genus. At the same time, sequ ence differences between the two organisms confirm that they are not t he same species. Three separate isolates of E. hellem were sequenced i n the highly variable intervening spacer region. The sequence was iden tical for all three isolates. Within the amplified DNA segment, region s were sequenced which yield highly variable, moderately variable and highly conserved sequence information, appropriate for comparison with other species in the phylum Microspora at all taxonomic levels. We su ggest that sequence data from these regions be included in future spec ies descriptions for the purposes of species identification and phylog enetic analysis. Restriction digests of the amplified region are prese nted and give a rapid method for distinguishing between the two Enceph alitozoon species.