Comparison between genome sequences of Chilean Tenacibaculum dicentrarchi isolated from red conger eel (Genypterus chilensis) and Atlantic salmon (Salmo salar) focusing on bacterial virulence determinants.

ABSTRACT

Tenacibaculum dicentrarchi is an emerging pathogen for salmonid cultures and red conger eel (Genypterus chilensis) in Chile, causing high economic losses not only in Chile but also to the global salmon industry. Infected fish show severe gross skin lesions that are sometimes accompanied by bone exposure. Despite pathogenicity demonstrated by Koch's postulates, no knowledge is currently available regarding the virulence machinery of T. dicentrarchi strains. Comparisons between the genome sequences of the eight T. dicentrarchi strains obtained from G. chilensis and Atlantic salmon (Salmo salar) provide insights on the existence of genomic diversity within this bacterium. The T. dicentrarchi type strain 3509T was used as a reference genome. Depending on the T. dicentrarchi strain, the discovered diversity included genes associated with iron acquisition mechanisms, copper homeostasis encoding, resistance to tetracycline and fluoroquinolones, pathogenic genomic islands and phages. Interestingly, genes encoding the T9SS membrane protein PorP/SprF were retrieved in all of the analysed T. dicentrarchi strains, regardless of the host fish (i.e. red conger eel or Atlantic salmon). However, the T6SS core component protein VgrG was identified in only one Atlantic salmon strain. Three types of peptidase genes and proteins associated with quorum sensing were detected in all of the T. dicentrarchi strains. In turn, all eight strains presented a total of 17 proteins associated with biofilm formation, which was previously confirmed through physiological studies. This comparative analysis will help elucidate and describe the genes and pathways that are likely involved in the virulence process of T. dicentrarchi. All or part of these predicted genes could aid the pathogen during the infective process in fish, making further physiological research necessary for clarification.