Terceti, Mateus de SouzaVences Lorenzo, AnaMatanza Fente, José ManuelDalsgaard, IngerPedersen, KarlRodríguez Osorio, Carlos2020-05-292020-05-292018Terceti MS, Vences A, Matanza XM, Dalsgaard I, Pedersen K and Osorio CR (2018) Molecular Epidemiology of Photobacterium damselae subsp. damselae Outbreaks in Marine Rainbow Trout Farms Reveals Extensive Horizontal Gene Transfer and High Genetic Diversity. Front. Microbiol. 9:2155. doi: 10.3389/fmicb.2018.02155http://hdl.handle.net/10347/22698The marine bacterium Photobacterium damselae subsp. damselae is a pathogen for a variety of marine animals, as well as for humans, and is nowadays considered an emerging pathogen for fish of importance in marine aquaculture. Recent studies have suggested that outbreaks in fish farms are caused by multiclonal populations of this subspecies that exist in the environment. Here, we report the study of a collection of 31 strains isolated during the course of disease outbreaks in marine rainbow trout farms in Denmark in 1994, 1995, and 2006, respectively. A phylogenetic analysis based on the toxR gene sequence, and the screening of virulence-related genes uncovered a high genetic heterogeneity, even among strains isolated from the same fish farm at the same time. Moreover, comparative analysis of the whole genome sequences of four selected strains revealed a large number of differentially occurring genes, which included virulence genes, pPHDD1 plasmid, polysaccharide synthesis gene clusters, CRISPR-Cas systems and putative new mobile genetic elements. This study provides sound evidence that P. damselae subsp. damselae outbreaks in Danish rainbow trout farms were caused by multiclonal populations and that horizontal gene transfer constitutes a strong driving force in the generation of intraspecific diversity in this pathogenengCopyright © 2018 Terceti, Vences, Matanza, Dalsgaard, Pedersen and Osorio. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these termshttp://creativecommons.org/licenses/by/4.0/Photobacterium damselaeVibriosisDamselysinPhobalysinHemolysinRainbow troutjournal article10.3389/fmicb.2018.021551664-302Xopen access