A) sodium chloride 1% B) sodium benzoate 20 mM pH 5.2. C) sodium nitrate 100 mM. Metabolism was monitored by measuring reduction of the tetrazolium dye in the medium at 15 min intervals and is shown as units. Because expression of dksA is required for S. flexneri virulence [27], and growth of Shigella in the intracellular environment may induce a stress response, we also measured invasion and plaque formation by the gluQ-rs mutant. However, MEK162 research buy no significant differences were noted (data not shown), suggesting that GluQ-RS is not essential for invasion or intracellular growth of S. flexneri. Discussion Conserved dksA-gluQ-rs genomic organization in gammaproteobacteria

GluQ-RS, a paralog of GluRS synthetase, is involved in the formation of GluQ, the nucleoside located at the wobble position of tRNAAsp in bacteria. The

protein is present in Firmicutes, Actinobacteria, Cyanobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Deltaproteobacteria (Figure 1). From the phylogenetic analysis we distinguished the three subgroups described previously [11] based on the HIGH motif that is present in the class I aminoacyl-tRNA synthetases [2]. As was described previously [11], all GluQ-RS enzymes are characterized by the replacement of a threonine in GluRS enzymes, which is involved in the recognition of the amino acid and the terminal adenosine of the tRNAGlu (Thr133 of Methanocaldococcus jannaschii GluRS enzyme) by isoleucine, leucine or valine at that position (Ile47 of S. flexneri GluQ-RS). GF120918 in vitro This substitution is also conserved in all enzymes analyzed here, including those from the Firmicutes group. The gluQ-rs gene is widely distributed in the bacterial domain; however, its genome organization is variable. We observed Methocarbamol that only in members of

the gammaproteobacteria, namely Aeromonadales, Alteromonadales, Pseudomonadaceae, Enterobacteriaceae and Vibrionaceae, the gluQ-rs gene is located immediately downstream of the dksA gene (Figure 1). A more detailed analysis shows that even within this genomic organization there are differences. In some species of Pseudomonadaceae, such as P. aeruginosa, P. entomophila, and P. fluorescens, we observed the same genomic structure as in E. coli or S. flexneri, with a distinctive terminator between the genes. In contrast, while the dksA gene is also upstream of gluQ-rs in some P. syringae, there are insertions of an encoded transposase or more than a 400 base pairs separating both genes without a detectable terminator. However, using bioinformatics tools we detected a possible promoter within this region in P. syringae (data not shown), indicating that the expression of the gluQ-rs gene may be under control of its own promoter, a question that remains to be addressed.