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

TLDR

Withering syndrome, a fatal disease of wild and cultured abalone along the west coast of North America, is caused by a member of the Rickettsiaceae family in the order Rickettsiales. The authors used morphological, serological, life‑history, and 16S rDNA genomic analyses, along with tissue staining, microscopy, PCR, and in situ hybridization, to identify and detect the bacterium. The bacterium, a Gram‑negative, obligate intracellular pleomorphic organism residing in membrane‑bound vacuoles of abalone gastrointestinal epithelial cells, cannot be cultured on synthetic media or fish cell lines, is susceptible to tetracyclines but not to chloramphenicol, clarithromycin or sarafloxacin, and is phylogenetically distinct within the alpha‑Proteobacteria, with a unique 16S rDNA sequence that differentiates it from related taxa.

Abstract

Withering syndrome is a fatal disease of wild and cultured abalone, Haliotis spp., that inhabit the west coast of North America. The aetiological agent of withering syndrome has recently been identified as a member of the family Rickettsiaceae in the order Rickettsiales. Using a combination of morphological, serological, life history and genomic (16S rDNA) characterization, we have identified this bacterium as a unique taxon and propose the provisional status of 'Candidatus Xenohaliotis californiensis'. The Gram-negative, obligate intracellular pleomorphic bacterium is found within membrane-bound 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 analysis based on the 16S rDNA of 'Candidatus Xenohaliotis californiensis' places 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 and alpha-4). The bacterium can be detected in tissue squashes stained with propidium iodide, microscopic examination of stained tissue sections, PCR or in situ hybridization. 'Candidatus Xenohaliotis californiensis' can be differentiated from other closely related alpha-Proteobacteria by its unique 16S rDNA sequence.