Discrimination between two Perkinsus spp. isolated from the softshell clam, Mya arenaria, by sequence analysis of two internal transcribed spacer regions and the 5 center dot 8S ribosomal RNA gene

The internal transcribed spacer (ITS-1 and ITS-2) regions and the 5.8S ribo somal RNA gene of 2 Perkinsus spp. (G117 and H49) originating from the soft shell clam, Mya arenaria, of the Chesapeake Bay were cloned and sequenced t o obtain evidence for their genetic divergence. A high level of heterogenei ty in both regions, probably resulting from deletions, insertions, and base substitutions, was evident from alignments of the sequences of the 2 isola tes with published sequences of other Perkinsus spp. The isolate G117 and o ther Perkinsus spp. were highly divergent (13-26 % and 19-20 % sequence div ergence in ITS-1 and ITS-2, respectively). These regions in the isolate H49 and Perkinsus marinus were similar (99.07 % and 99 % for ITS-1 and ITS-2, respectively). Evidence obtained from a phylogenetic analysis using the ali gned sequences suggests that G117 and H49 belong to 2 distinct species of P erkins rls. The isolate G117 possibly belongs to an as yet undescribed spec ies of Perkinsus, and H49 belongs to the species P. marinus. The conclusion s drawn from the genetic analysis of H49 and G117 are supported by previous ly reported morphological characteristics (McLaughlin & Faisal, 1998b). Iso lates H49 and G117 originated from the same molluscan species demonstrating that at least 2 different species of Perkinsus call co-exist in 1 host.