Action in pairs

EditoriaL EditoriaL Yersinia ruckeri is a gram-negative rod-shaped bacterium belonging to the family Enterobacteriaceae. It is in the same genus as Yersinia pestis, the causative agent of the bubonic plaque and a category A select agent. The taxonomic assignment of Y. ruckeri, however, has raised controversy since it appears to have diverged from the rest of the Yersinia genus in phylogenetic analysis. 1 Y. ruckeri is the causative agent of enteric redmouth (ERM) disease in salmonids, known as yersiniosis, and can cause significant economic losses, particularly in the rainbow trout farming industry. 2 Clinical signs include hemorrhaging around the mouth, intestines and other organs. Y. ruckeri is naturally associated with the aquatic environment and is thought to initially infect via adhesion to the gill surface. While most research effort has been focused on characterizing human pathogens, studies of their closely related non-patho-genic-to-human relatives have been largely overlooked although it has been recognized that many human pathogens have actually emerged very recently from protean environmental, commensal, or zoonotic populations, and there are similarities in the genomic, biochemical levels among these strains. 3,4 This is also the case for research on Y. ruckeri despite its importance in aquaculture. Most research attention in species of the Yersinia genus is focused on the three well-known human pathogens, Y. pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica. For example, the virulence mechanisms of Y. pes-tis have been well studied 5 because it has caused approximately 200 million human deaths historically, with at least 2000 cases of plague reported annually by the World Health Organization (WHO). However, there are only a few pathogenic mechanisms of Y. ruckeri that have been described so far. Some of these mechanisms have been proven to be involved in virulence, such as the iron uptake mechanism via the siderophore natural product ruckerbatin 6 and the YhlA hemolysin 7 and a new type of two-component operon that contains an amino acid permease motif and an l-cysteine desulfidase motif. 8 The operon was confirmed to be involved in the regulation of cysteine uptake, and knockout of this operon abolishes virulence of Y. ruckeri in fish. Y. ruckeri was also found to produce an antibiotic natural product holo-mycin, 9 a founding member of a unique family of dithiolopyrro-lone natural products. 10 Interestingly, holomycin production was also found to have a connection with the regulation of cysteine uptake. 11 It remains to be shown whether holomycin production …