Molecular evidence that the proliferative kidney disease organism unknown (PKX) is a myxosporean

The proliferative kidney organism unknown (PKX), a serious salmonid fish pathogen, is considered to be a myxosporean on the basis of ultrastructural studies, but its real taxonomic position has never been confirmed. In order to ascertain its position, genomic DNA was extracted from PKX and small subunit (SSU) ribosomal DNA was amplified by PCR, cloned and sequenced. A phylogenetical analysis on SSU rDNA from 76 or 128 eucaryotic species was carried out. Whatever the tree reconstruction methods used, PKX was found to be a sister group of the Myxozoa phylum, providing the first molecular evidence for its membership in this phylum.