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

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