Similarly 0.5 mM of CuOOH abolished growth of ohr strain but did not affect growth yield of ohrR and parental strains. Disk diffusion assays were used to determine if ohr and ohrR mutations affected resistance to ROS. The ohr mutant was less resistant than its parental strain when challenged with organic peroxides as shown by the zones of growth inhibition: 4.1 ± 0.2 cm for CuOOH and 3.1 ± 0.1 cm for tBOOH versus to 2.3 ± 0.2 and 2.5 ± 0.3 cm for wild type strain. In contrast, ohrR mutation did not affect the resistance of S. meliloti against tBOOH and CuOOH since inhibition zones were not significantly (p value

≤ 0.01) different from those of wild type strain (Figure 1). The ohr-ohrR mutant behaved identically to the ohr mutant (Figure 1). Figure 1 Resistance of the ohr and ohrR mutants to ROS. The resistance of wild type (WT), ohr, this website ohrR, ohr-ohrR mutants and ohr mutant complemented Salubrinal research buy by plasmids pBBR1-MSC2 [ohr (pBB2)] and pBBohr [ohr (pBBohr)] was analysed by

disk diffusion assay on LB plates as described in methods. The data correspond to five independent experiments; standard deviation is indicated (bars). In other experiments, ohr and ohrR mutants were complemented by the moderate copy number plasmid pBBR1-MCS2 bearing wild type alleles of ohr (pBBohr) or ohrR (pBBohrR). The empty vector did not affect the resistance of wild type or mutants against tBOOH and CuOOH. Plasmid vector carrying ohrR + allele also did not affect the resistance to OHPs of these three strains. In contrast the introduction of pBBohr in ohr mutant dramatically improved resistance to both tBOOH and CuOOH (Figure 1). These results showed that Ohr is important in the defence against organic peroxides in S. meliloti. In comparison with parental strain, ohr and ohrR mutants were not significantly affected in resistance to H2O2 and menadione; inhibition zones were nearly identical for the three strains. No alteration of this resistance was observed after complementation of the mutations with pBBohr or pBBohrR. This result agrees with the role of Ohr in other Tideglusib organisms and its specificity for

organic peroxide resistance. Regulation of ohr and ohrR genes The transcriptional activity of ohr and ohrR genes was assayed in strain R7.16 carrying ohr::lacZ and ohrR::uidA transcriptional fusions in tandem with wild type copies of ohr and ohrR genes. The click here expression of these fusions was analysed in LB medium and in the minimal medium GAS. No difference was observed between both media. The expression of ohr::lacZ and ohrR::uidA was followed throughout growth till the late stationary growth phase. The expression of these two genes remained constant; no variation was observed after growth arrest. Adding NaCl to the medium during exponential growth or during stationary growth phase did not affect ohr or ohrR expression (data not shown).