‘Cand. Actinochlamydia clariae’ gen. nov., sp. nov., a Unique Intracellular Bacterium Causing Epitheliocystis in Catfish (Clarias gariepinus) in Uganda

Abstract

Background and ObjectivesEpitheliocystis, caused by bacteria infecting gill epithelial cells in fish, is common among a large range of fish species in both fresh- and seawater. The aquaculture industry considers epitheliocystis an important problem. It affects the welfare of the fish and the resulting gill disease may lead to mortalities. In a culture facility in Kampala, Uganda, juveniles of the African sharptooth catfish (Clarias gariepinus) was observed swimming in the surface, sometimes belly up, showing signs of respiratory problems. Histological examination of gill tissues from this fish revealed large amounts of epitheliocysts, and also presence of a few Ichthyobodo sp. and Trichodina sp.Methods and ResultsSequencing of the epitheliocystis bacterium 16S rRNA gene shows 86.3% similarity with Candidatus Piscichlamydia salmonis causing epitheliocystis in Atlantic salmon (Salmo salar). Transmission electron microscopy showed that the morphology of the developmental stages of the bacterium is similar to that of members of the family Chlamydiaceae. The similarity of the bacterium rRNA gene sequences compared with other chlamydia-like bacteria ranged between 80.5% and 86.3%. Inclusions containing this new bacterium have tubules/channels (termed actinae) that are radiating from the inclusion membrane and opening on the cell surface or in neighbouring cells.ConclusionsRadiation of tubules/channels (actinae) from the inclusion membrane has never been described in any of the other members of Chlamydiales. It seems to be a completely new character and an apomorphy. We propose the name Candidatus Actinochlamydia clariae gen. nov., sp. nov. (Actinochlamydiaceae fam. nov., order Chlamydiales, phylum Chlamydiae) for this new agent causing epitheliocystis in African sharptooth catfish.

Ca. Similichlamydia in Epitheliocystis Co-infection of Gilthead Seabream Gills: Unique Morphological Features of a Deep Branching Chlamydial Family

“…Actinochlamydia (Steigen et al, 2013). A condensed nucleoid is typically localized in a polar fashion adjacent to the bacterial membrane with an array of filaments (actinae, Steigen et al, 2013) penetrating the membrane on an adjacent or opposite side, indicative of a polarized bacterial cell with clearly defined functional regions.…”

“…Piscichlamydia from epitheliocystis lesions in brown trout ( Salmo trutta , Schmidt-Posthaus et al, 2012), indicating that this mechanism may be common for the entire deep rooted clade comprising the four putative families ( Ca . Piscichlamydia, Similichlamydia, Parilichlamydia, Actinochlamydia), all members of which have only been found as intracellular bacterial pathogens of marine or fresh water vertebrates, indicative of their early evolutionary origins and specialization for an aqueous environment (Draghi et al, 2004; Schmidt-Posthaus et al, 2012; Steigen et al, 2013, 2015; Stride et al, 2013a,b,c). Curiously, the large RBs with multiple nucleoids which we find commonly here (Figures 3C,D) are more reminiscent of the aberrant bodies generated by antibiotic treatment or nutrient restriction in the Chlamydiaceae (Polkinghorne et al, 2006).…”

“…Actinochlamydia (Steigen et al, 2013), which could temptingly be postulated to influence host recognition and uptake. A major caveat, indeed a caveat which applies to the majority of the EM studies with Chlamydia , is that the use of chemical fixation combined with classical dehydration procedures prior to embedding can lead to a range of artifacts and poor membrane preservation.…”

“…Similichlamydiaceae infecting striped trumpeter ( Latris lineata ) and barramundi ( Lates calcarifer ) (Stride et al, 2013b,c), Ca . Actinochlamydiaceae causing epitheliocystis in catfish ( Clarius gariepinus ) in a Ugandan lake system (Steigen et al, 2013), and new species of the Ca . Similichlamydiaceae infecting ballan wrasse ( Labrus bergylta ) used as cleaner fish in salmon farms off the Norwegian coast (Steigen et al, 2015).…”

A Zebrafish Model for Chlamydia Infection with the Obligate Intracellular Pathogen Waddlia chondrophila

“…Similichlamydiaceae (Stride et al, 2013b,c; Steigen et al, 2015; Seth-Smith et al, this issue), and Ca. Actinochlamydiaceae (Steigen et al, 2013). In a ground breaking study, Lagkouvardos and colleagues discovered up to 181 new putative families of the Chlamydiae from primarily marine and fresh water sources, of which the Waddliaceae formed a prominent clade (Lagkouvardos et al, 2014).…”