Abstract
Despite the existence of a commercial vaccine routinely used to protect salmonids against Yersinia ruckeri, outbreaks still occur, mainly caused by nonmotile and lipase‐negative strains (serotype O1 biotype 2). Moreover, epizootics caused by other uncommon serotypes have also been reported. At the moment, one of the main concerns for the aquaculture industry is the expanding range of hosts of this pathogen and the emergence of new biotypes and serotypes causing mortality in fish farms and against which the vaccine cannot protect. The comparative analysis of the genome sequences of five Y. ruckeri strains (150, CSF007‐82, ATCC29473, Big Creek 74, and SC09) isolated from different hosts and classified into different serotypes revealed important genetic differences between the genomes analyzed. Thus, a clear genetic differentiation was found between serotype O1 and O2 strains. The presence of 99 unique genes in Big Creek 74 and 261 in SC09 could explain the adaptation of these strains to salmon and catfish, respectively. Finally, the absence of 21 genes in ATCC29473 which are present in the other four virulent strains could underpin the attenuation described for this strain. The study reveals important genetic differences among the genomes analyzed. Further investigation of the genes highlighted in this study could provide insights into the understanding of the virulence and niche adaptive mechanisms of Y. ruckeri.
Highlights
Yersinia ruckeri is a gram-negative rod-shaped bacterium able to infect different fish species such as rainbow trout, carp, catfish, sturgeon, burbot, and perch
This result suggests that Y. ruckeri strains belonging to serotype O1 and having rainbow trout as a host (150, ATCC29473, CSF007-82) are genetically more similar to each other than to other serotypes isolated from different animals, suggesting that differences in cell surface antigens and host specificity may have a markedly genetic base
While serotype O1 strains isolated from rainbow trout have few unique genes (150 has none), the other two strains, Big Creek74 and SC09, have a great number, 99 and 261, respectively
Summary
Yersinia ruckeri is a gram-negative rod-shaped bacterium able to infect different fish species such as rainbow trout, carp, catfish, sturgeon, burbot, and perch. In salmonids, it causes enteric red mouth disease (ERM), a serious septicemic fish disease which is a major problem for aquaculture industries all over the world. Despite the existence of a reasonably effective immersion vaccine, outbreaks still occur, produced mainly by nonmotile and lipase-negative strains (Arias et al, 2007; Austin, Robertson, & Austin, 2003; Calvez, Gantelet, Blanc, Douet, & Daniel, 2014; Fouz, Zarza, & Amaro, 2006) The study reveals data that are important for a better understanding of the mechanisms underlying the niche adaptation and virulence of Y. ruckeri
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