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

Abstract

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.

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

“…4 ). This is in compliance with previous phylogenies using 16S rRNA sequences (Contador et al 2016 ; Seth-Smith et al 2016 ; Cascarano and Katharios 2022 ; Cascarano et al 2022 ). Consequently, it is reasonable to believe that all taxa of this clade share the same common ancestor of Cand .…”

“…Ichtyocystis hellenicum). Recent studies have identified new agents of this genus associated with epitheliocystis in reared greater amberjack ( Seriola dumerili ), wild-caught Pacific herring ( Clupea pallasii ) and Pacific mackerel ( Scomber japonicus ) (Cascarano et al 2022 ), as well as from pompano ( Trachinotus ovatus ) (Cascarano and Katharios 2022 ).…”

“…A single locus 16S rRNA Bayesian phylogenetic analysis including 37 representative type strains of Betaproteobacteria and 17 bacterial strains associated with epitheliocystis in fish (Contador et al 2016 ; Seth-Smith et al 2016 ; Cascarano et al 2022 ; Cascarano and Katharios 2022 ) was conducted in MrBayes. Pseudomonas aeruginosa strain PAO1 T was used as an outgroup.…”

“…Ichthyocystis spp., causing epitheliocystis in fish species, have also been identified, and based on 16S rRNA analyses these bacteria represent close relatives to Cand . B. cysticola (Seth-Smith et al 2016 ; Cascarano et al 2022 ; Cascarano and Katharios 2022 ). Even though 16S rRNA is the only common sequence information available from these Candidatus species, it could be assumed that they all belong to the same family within Betaproteobacteria.…”

“…The continuous expansion of epitheliocystis outbreaks associated with Betaproteobacteria in fish species worldwide (Contador et al 2016 ; Seth-Smith et al 2016 ; Cascarano et al 2022 ; Cascarano and Katharios 2022 ), stresses the need for a clarification/refining of the taxonomic affiliations of these bacteria. We hence propose a revised taxonomic classification of Cand .…”