Conclusions The S. meliloti LGX818 RNA chaperone Hfq is a pleiotropic

regulator influencing central metabolic pathways in free-living bacteria and several aspects of the symbiosis with its legume host alfalfa: nodulation competitiveness, survival of endosymbiotic bacteria within the nodule cells and expression of the key regulators of nitrogen-fixation. The identified Hfq-dependent phenotypes, mRNAs and sRNAs in a beneficial plant-interacting rhizobacteria such as S. meliloti constitute a new baseline to further investigate the Hfq-mediated pathways controlling common strategies of phylogenetically distant bacteria to colonize, infect and survive within their eukaryotic host cells. Methods selleck inhibitor Bacterial strains, plasmids, media and growth conditions Bacterial strains and plasmids used in this study along with their relevant characteristics are listed in Table 1. S. meliloti wild-type and hfq mutant derivative strains were routinely grown in complex tryptone-yeast TY [64] or defined MM media Tariquidar nmr [65] at 30°C and E. coli strains in Luria-Bertani (LB) medium at 37°C. For microaerobic growth bacteria were initially grown in 25 ml of TY medium in aerated shaken flasks to O.D600 nm 0.5. Cultures were then flushed with a 2% oxygen-98%

argon gas mixture during 10 min and incubated for a further 4 h. Antibiotics were added to the media when required at the Idelalisib purchase following final concentrations: streptomycin (Sm), 250 μg/ml; ampicillin (Ap), 200 μg/ml; tetracycline (Tc), 10 μg/ml; and kanamycin (Km), 50 μg/ml for E. coli and 180

μg/ml for rhizobia. Table 1 Bacterial strains and plasmids. Strain/Plasmid Relevant characteristics Reference/Source Bacteria     S. meliloti        1021 Wild-type SU47 derivative, Smr [75]    2011 Wild-type SU47 derivative, Smr [76]    1021Δhfq 1021 hfq mutant strain, Smr This work    2011-1.2 2011 hfq insertion derivative (control str.), Smr, Kmr This work    2011-3.4 2011 hfq insertion mutant, Smr, Kmr This work    1021hfq FLAG 1021 derivative expressing a 3 × Flag-tagged Hfq, Smr This work E. coli        DH5α F- endA1, glnV44, thi-1, recA1, relA1, gyrA96, deoR, nupG, φ80d, lacZΔM15 Δ(lacZYA-argF)U169, hsdR17(rK – mK +), λ- Bethesda Research Lab. Plasmids        pRK2013 Helper plasmid, ColE1, Kmr [77]    pGEM®-T Easy Cloning vector for PCR, Apr Promega Corporation    pK18mobsacB Suicide vector in S. meliloti Kmr, sacB, oriV [78]    pJB3Tc19 Broad host-range IncP cloning vector, Apr, Tcr [79]    pBluescriptII KS+ Multicopy cloning vector, Apr Stratagene    pGEMhfq 1,684-bp of hfq genomic region in pGEM-T This work    pK18_1.2 Internal fragment of hfq ORF in pK18mobsacB This work    pK18_3.