PHYLOGENETIC PLACEMENT OF NUCLEAR INCLUSION-X (NIX) INTO THE GAMMA-SUBCLASS OF PROTEOBACTERIA ON THE BASIS OF 16S RIBOSOMAL-RNA SEQUENCE COMPARISONS

Nuclear Inclusion X (NIX) is an obligate intranuclear pathogen which has been associated with severe mortality of the Pacific razor clam, Siliqua patula. We have developed procedures to isolate the organism, and purify its RNA. A partial sequence (692 bases) was determined by directly sequencing the 16S rRNA using a modified Sanger dideoxy chain termination method. Analysis of the sequence data indicated that the NIX organism is a member of the gamma subclass of the eubacterial class Proteobacteria. Comparison of the NIX sequence with those of over 100 gamma proteobacteria revealed no closely related organisms. NIX sequence is most similar to that of Pseudomonas aeruginosa and Cardiobacterium hominis, at a level of about 89 percent. This relatively distant relationship suggests that NIX represents a novel genus.