coli control (Fig. 5, lane 4). Twenty-five years after its characterization as an obligate intracellular Alphaproteobacteria (Fryer et al., 1992), it has only recently been demonstrated that P. salmonis Epacadostat is truly a free-living bacterial pathogen, belonging to the Gammaproteobacteria group (Fryer & Hedrick, 2003). The bacteria is known to survive in either fresh (Graggero et al., 1995) or marine waters (Olivares & Marshall, 2010) and moreover it is also known

to be highly adaptable when exposed to limiting and/or stressing conditions, which mimics its natural situation in the oceans (Rojas et al., 2008). Additionally, the presence of insertion sequences and putatively other mobile genetic elements in P. salmonis represents a solid evidence that the adaptability potential of the bacteria resides in its versatile genome (Marshall et al., 2011). In this context, the description of a TA locus in P. salmonis appears to be a natural consequence of this versatility. Indeed, TA loci are conserved (often in multiple copies) in the genomes of many organisms that can cause persistent infections and/or persist in the environment: M. tuberculosis, Helicobacter pylori, Coxiella burnetii, Leptospira interrogans, Vibrio cholerae, Ceritinib mouse and Salmonella

enterica serovars Typhi and Typhimurium, as well as Haemophilus influenzae, are good examples of this fact (Daines et al., 2007). Additionally, it is important to consider that TA loci are highly abundant in free-living bacteria, but

lost from host-associated microorganisms (Pandey & Gerdes, 2005). To date, nine TA families have been reported in the literature: VapBC, RelE, ParE, MAzF, Doc, HipA, HigB, CcdB, and ω-ɛ-ζ (Van Melderen & Saavedra De Bast, 2009). The VapBC is the largest family of bacterial TA modules, representing close to 40% of all the TA loci known, and grouped together by virtue of their toxin components, in most cases belong to the PilT N-terminal domain family of proteins, which in turn function as ribonucleases (Cooper et al., 2009; Robson et al., 2009). Thus, it appears logical and important to identify TA loci in emerging 2-hydroxyphytanoyl-CoA lyase prokaryotic organisms in order to improve our understanding of these systems, and more broadly, in attempting to understand the cellular mechanisms behind bacterial adaptation (Sevin & Barloy-Hubler, 2007). We have characterized a new and functional bicistronic operon that encodes the two genes of a Type II TA module in P. salmonis. The organization of the P. salmonis TA locus shows many characteristics of other bacterial TA modules. The presence of IRs in the promoter region (Fig. 1) is a feature that is present in various Type II TA systems, such as the vapBC and ChpK operons of L. interrogans (Picardeau et al., 2001; Zhang et al., 2004). The localization of the antitoxin gene upstream of the toxin ORF is a distinctive feature shared by all Type II TA loci homologous to the P. salmonis system. The P.