1Medical Technology Program, Department of
Microbiology, Michigan State University, East Lansing, Michigan 48824-1031
2Department of Ophthalmology,
Emory University School of Medicine, Atlanta, Georgia 30322
3Department of Plant and
Microbial Biology, University of California, Berkeley, California
94720-3102 and
4Department of
Microbiology, Faculty of Medicine, University of Peradeniya,
Peradeniya 20400, Sri Lanka
Received 26 February 1999/Returned for modification 4 May 1999/Accepted 25 May 1999
For the past 100 years the phylogenetic affinities of Rhinosporidium seeberi have been controversial. Based on its morphological features, it has been classified as a protozoan or as a member of the kingdom Fungi. We have amplified and sequenced nearly a full-length 18S small-subunit (SSU) ribosomal DNA (rDNA) sequence from R. seeberi. Using phylogenetic analysis, by parsimony and distance methods, of R. seeberi's 18S SSU rDNA and that of other eukaryotes, we found that this enigmatic pathogen of humans and animals clusters with a novel group of fish parasites referred to as the DRIP clade (Dermocystidium, rossete agent, Ichthyophonus, and Psorospermium), near the animal-fungal divergence. Our phylogenetic analyses also indicate that R. seeberi is the sister taxon of the two Dermocystidium species used in this study. This molecular affinity is remarkable since members of the genus Dermocystidium form spherical structures in infected hosts, produce endospores, have not been cultured, and possess mitochondria with flat cristae. With the addition of R. seeberi to this clade, the acronym DRIP is no longer appropriate. We propose to name this monophyletic clade Mesomycetozoa to reflect the group's phylogenetic association within the Eucarya.