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

The internal transcribed spacer (ITS-1 and ITS-2) regions and the 5·8S ribosomal RNA gene of 2 Perkinsus spp. (G117 and H49) originating from the softshell clam, Mya arenaria , of the Chesapeake Bay were cloned and sequenced to obtain evidence for their genetic divergence. A high level of heterogeneity in both regions, probably resulting from deletions, insertions, and base substitutions, was evident from alignments of the sequences of the 2 isolates with published sequences of other Perkinsus spp. The isolate G117 and other Perkinsus spp. were highly divergent (13–26% and 19–20% sequence divergence 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 aligned sequences suggests that G117 and H49 belong to 2 distinct species of Perkinsus . The isolate G117 possibly belongs to an as yet undescribed species of Perkinsus , and H49 belongs to the species P. marinus . The conclusions drawn from the genetic analysis of H49 and G117 are supported by previously reported morphological characteristics (McLaughlin & Faisal, 1998 b ). Isolates H49 and G117 originated from the same molluscan species demonstrating that at least 2 different species of Perkinsus can co-exist in 1 host.