Characterization of ‘Candidatus Clavochlamydia salmonicola’: an intracellular bacterium infecting salmonid fish

Abstract

The phylum Chlamydiae contains obligate intracellular bacteria, several of which cause disease in their hosts. Morphological studies have suggested that this group of bacteria may be pathogens of fish, causing cysts in epithelial tissue - epitheliocystis. Recently, the first genetic evidence of a chlamydial aetiology of this disease in seawater reared Atlantic salmon from Norway and Ireland was presented, and the agent was given the name 'Candidatus Piscichlamydia salmonis'. In this article we present molecular evidence for the existence of a novel Chlamydiae that also may cause epitheliocystis in Norwegian salmonids. This novel Chlamydiae has been found in salmonid fish from freshwater, and based on its partial 16S rRNA gene, it may constitute a third genus in the family Chlamydiaceae, or a closely related sister family. By using whole-mount RNA-RNA hybridization we demonstrate how infected cells are distributed in a patchy manner on a gill arch. The morphology of the novel Chlamydiae includes the characteristic head-and-tail cells that have been described earlier from salmonid fish suffering from epitheliocystis. We propose the name 'Candidatus Clavochlamydia salmonicola' for this agent of epitheliocystis in freshwater salmonids.

Molecular Characterization of “Candidatus Parilichlamydia carangidicola,” a Novel Chlamydia-Like Epitheliocystis Agent in Yellowtail Kingfish, Seriola lalandi (Valenciennes), and the Proposal of a New Family, “Candidatus Parilichlamydiaceae” fam. nov. (Order Chlamydiales)

“…Piscichlamydia salmonis" (24) and "Ca. Clavochlamydia salmonicola" (25), there is no single genus for Chlamydia-like bacteria associated with epitheliocystis (15). With the addition of this novel CLO, there are now three nearly full-length 16S rRNA sequences, all with Ͻ90% sequence similarity.…”

“…In salmonids, epitheliocystis infection was associated only with mild lesions of the branchial epithelium, and any proliferative response was not associated with epitheliocystis (25,33). The histological and electron microscopic features observed in YTK support the corresponding molecular result of a CLO being present within the epitheliocystis cysts.…”

“…Although this condition has been reported for over 80 years, the causative agent or agents of epitheliocystis have yet to be successfully cultured in vitro. Only recently have three of the etiological agents of epitheliocystis been more completely described as belonging to the order Chlamydiales, a group of obligate intracellular bacteria sharing unique and complex developmental cycles (15,(23)(24)(25)(26)(27), whereas four additional organisms have been characterized using molecular methods and phylogenetic analyses (15,24,27).…”

Chlamydia abortus: New Aspects of Infectious Abortion in Sheep and Potential Risk for Pregnant Women

“…As a consequence many of the scientific community have declined use of the term Chlamydophila and have followed the concept of a one-genus, multiple species nomenclature [3], as proposed in Bergey's Manual of Systematic Bacteriology 2011 [4]. Since then, and with the identification of an increasing number of additional chlamydial species [5,6], the number of genera within the Chlamydiaceae has expanded to include Clavochlamydia [7] and Amphibiichlamydia [8,9] and a total of 15 species (Table 1).…”

Molecular Characterization of “Candidatus Similichlamydia latridicola” gen. nov., sp. nov. (Chlamydiales: “Candidatus Parilichlamydiaceae”), a Novel Chlamydia-Like Epitheliocystis Agent in the Striped Trumpeter, Latris lineata (Forster)

“…In determining the causes of these health issues, epitheliocystis was also described in these fish (6). The latter disease is a condition of the skin and gills and is generally associated with infections by Chlamydia-like organisms (CLOs) (7)(8)(9)(10). These CLOs are Gram-negative, intracellular bacteria that may cause cyst-like lesions in the gill lamellae (9,11,12).…”