However, a 5 nucleotide

substitution of the most conserved residues at ABS-1 site (pompW/ABS1-lacZ) resulted in no regulation after exposure to either of the toxic compounds (1,09 ± 0.104 and 0,93 ± 0.061), indicating that they are relevant for the transcriptional activity of ompW in response to H2O2 and HOCl (Figure 5B). Furthermore, these results are in agreement with EMSAs which indicate that ArcA only binds to fragments containing ABS-1. The ArcAB two component system mediates ompW negative regulation To establish a direct relationship between ompW negative regulation and ArcA-P binding to its promoter region, ompW expression was evaluated by qRT-PCR in a ∆arcA strain exposed to H2O2 and HOCl. The negative regulation observed in the wild type strain #Histone Methyltransferase inhibitor randurls[1|1|,|CHEM1|]# was not retained in an arcA mutant treated

with either of the toxic compounds and ompW transcript levels were similar as those observed in untreated cells. Genetic complementation of ∆arcA restored the negative regulation observed in wild type cells exhibiting lower ompW mRNA levels (0.161 ± 0.068 and 0.488 ± 0.027, respectively) as compared to untreated cells (Figure 6A and C). Growth of the genetically complemented strain in the presence of glucose (non-induction) Rabusertib resulted in similar ompW mRNA levels between treated and untreated cells (data not shown). As controls, we measured ompD ompC and arcB transcript levels after exposure to H2O2 and HOCl in a ∆arcA strain. Transcript levels of ompD were measured since its expression is regulated by ArcA under ROS conditions [12]. Our results indicate that neither PIK3C2G ompD or arcB transcript levels were decreased after exposure to H2O2 or HOCl while those of ompC remained regulated in a ∆arcA strain treated with either of the toxic compounds (Figure 6A), confirming that ArcA mediates ompD regulation under ROS conditions and showing that the expression of ompC is ArcA independent and regulated by different mechanisms which remain unsolved to the date, and are under study in our laboratory. Furthermore, our bioinformatic analyses in search for ArcA motifs

predicted binding sites in the promoter regions of ompW and ompD, but not for ompC ([12], data not shown). Figure 6 ArcAB-dependant expression of ompW . ompW, ompD, ompC, arcB and arcA mRNA levels were measured by qRT-PCR in a (A) ∆arcA, (B) ∆arcB and (C) ∆arcA/pBAD-arcA and ∆arcB/pBAD-arcB. arcB and arcA were used as negative controls in (A) and (B), respectively. Exponentially growing cells were treated with H2O2 1.5 mM or NaOCl 530 μM for 20 min and transcript levels were measured. Genetically complemented cells were grown in the presence of arabinose 1 mM. Control cells received no treatment. 16S rRNA levels were used for normalization. Values represent the average of three independent experiments ± SD. To determine whether the negative regulation by ArcA was dependant on its cognate sensor ArcB, ompW mRNA levels were evaluated in a ∆arcB strain.