'Candidatus Xenohaliotis californiensis', a newly described pathogen of abalone, Haliotis spp., along the west coast of North America

Withering syndrome is a fatal disease of wild and cultured abalone. Halioti s spp., that inhabit the west coast of North America. The aetiological agen t of withering syndrome has recently been identified as a member of the fam ily Rickettsiaceae in the order Rickettsiales. Using a combination of morph ological, serological, life history and genomic (16S rDNA) characterization . we have identified this bacterium as a unique taxon and propose the provi sional status of 'Candidatus Xenohaliotis californiensis', The Gram-negativ e. obligate intracellular pleomorphic bacterium is found within membrane-bo und vacuoles in the cytoplasm of abalone gastrointestinal epithelial cells. The bacterium is not cultivable on synthetic media or in fish cell lines ( e.g. CHSE-214) and may be controlled by tetracyclines (oxytetracycline) but not by chloramphenicol, clarithromycin or sarafloxicin. Phylogenetic analy sis based on the 16S rDNA of 'Candidatus Xenohaliotis californiensis' place s it in the alpha-subclass of the class Proteobacteria but not to the four recognized subtaxa of the alpha-Proteobacteria (alpha-1, alpha-2, alpha-3 a nd alpha-4). The bacterium can be detected in tissue squashes stained with propidium iodide, microscopic examination of stained tissue sections, PCR o r in situ hybridization. 'Candidatus Xenohaliotis californiensis' can be di fferentiated from other closely related alpha-Proteobacteria by its unique 16S rDNA sequence.