Epitheliocystis in Greater Amberjack: Evidence of a Novel Causative Agent, Pathology, Immune Response and Epidemiological Findings

Phylogenetic analyses of Candidatus Branchiomonas cysticola refine the taxonomic classification of Betaproteobacteria associated with epitheliocystis in fish

Candidatus Branchiomonas cysticola is recognized as the most prevalent bacterial agent causing epitheliocystis in Atlantic salmon (Salmo salar). Based on its partial 16S rRNA sequence, the bacterium has previously been found to be a member of Burkholderiales in the class Betaproteobacteria. Multilocus Sequence Analysis (MLSA) of the bacterium and 60 type strains of Betaproteobacteria using newly identified housekeeping genes (dnaK, rpoC, and fusA) and ribosomal subunit sequences (16S and 23S), instead supported the bacterium's affiliation to Nitrosomodales. Taxonomic rank normalization by Relative Evolutionary Divergence (RED) showed the phylogenetic distinction between Cand. B. cysticola and its closest related type strain to be at the family level. A novel bacterial family named Branchiomonaceae has thus been proposed to include a monophyletic clade of Betaproteobacteria exclusively associated with epitheliocystis in fish.

Expansion of the Beta-Proteobacterial Genus Ca. Ichthyocystis: A Case Report of Epitheliocystis in the Pompano Trachinotus ovatus

Epitheliocystis is a disease caused by a wide variety of host-specific intracellular bacteria infecting fish gills. In the Mediterranean Sea, epitheliocystis has been recently associated with a novel genus of beta-proteobacteria, the Ca. Ichthyocystis genus. In the present study, we report a case of epitheliocystis in a wild-caught specimen of pompano Trachinotus ovatus in Crete, Greece. Molecular analysis of partial 16s rRNA sequence led to the discovery of a putative novel species of the Ca. Ichthyocystis genus. Investigation of the phylogenetic relationship between closely related sequences deposited in NCBI suggests that bacterial ancestors in gilthead seabream might have a pivotal role in the differentiation of genus.