Genetic and physiological analysis of the major OxyR-regulated katA from Xanthomonas campestris pv. phaseoli

Inactivation of ahpC renders Stenotrophomonas maltophilia resistant to the disinfectant hydrogen peroxide

Inactivation of ahpC, encoding alkyl hydroperoxide reductase, rendered Stenotrophomonas maltophilia more resistant to H₂O₂; the phenotype was directly correlated with enhanced total catalase activity, resulting from an increased level of KatA catalase. Plasmid-borne expression of ahpC from pAhpC_sm could complement all of the mutant phenotypes. Mutagenesis of the proposed AhpC peroxidactic and resolving cysteine residues to alanine (C47A and C166A) on the pAhpC_sm plasmid diminished its ability to complement the ahpC mutant phenotypes, suggesting that the mutagenized ahpC was non-functional. As mutations commonly occur in bacteria living in hostile environment, our data suggest that point mutations in ahpC at codons required for the enzyme function (such as C47 and C166), the AhpC will be non-functional, leading to high resistance to the disinfectant H₂O₂.

Molecular mechanism involved in the response to hydrogen peroxide stress in Acinetobacter oleivorans DR1

Two-dimensional gel electrophoresis was conducted to investigate the effect of H2O2 on whole protein expression in Acinetobacter oleivorans DR1. Functional classification of 13 upregulated proteins using MALDI-TOF mass spectrometry showed relationships with oxidative stress, energy production and conversion, nucleotide and amino acid metabolism, membrane-related, ion transport, and chaperone-related functions. Alignment of OxyR-binding regions from Pseudomonas aeruginosa and Escherichia coli with promoters of identified proteins revealed that only ahpC, ahpF, and trxB (thioredoxin-disulfide reductase) genes, along with a newly found oprC (putative outer membrane receptor protein) gene, have OxyR-binding sites. The oxyR and ahpC mutants were more sensitive to H2O2 and showed growth defects in both nutritional and n-hexadecane-amended media. Four catalases present in the genome of A. oleivorans DR1 were not detected, which led us to confirm the expression and activity of those catalases in the presence of H2O2. The expression patterns of the four catalase genes differed at different concentrations of H2O2. Interestingly, the promoters of both known OxyR-controlled katG gene (AOLE_17390) and putative small catalase gene (AOLE_09800) have OxyR-binding sites. Gel-shift assay confirmed OxyR binding to the promoter regions of newly identified OxyR-controlled genes encoding OprC and a putative catalase. Hierarchical expression and OxyR-binding of several OxyR-controlled genes suggested that concentration is an important factor in inducing the set of genes under H2O2 stress.

The roles of peroxide protective regulons in protecting Xanthomonas campestris pv. campestris from sodium hypochlorite stress

The exposure of Xanthomonas campestris pv. campestris to sublethal concentrations of a sodium hypochlorite (NaOCl) solution induced the expression of genes that encode peroxide scavenging enzymes within the OxyR and OhrR regulons. Sensitivity testing in various X. campestris mutants indicated that oxyR, katA, katG, ahpC, and ohr contributed to protection against NaOCl killing. The pretreatment of X. campestris cultures with oxidants, such as hydrogen peroxide (H2O2), t-butyl hydroperoxide, and the superoxide generator menadione, protected the bacteria from lethal concentrations of NaOCl in an OxyR-dependent manner. Treating the bacteria with a low concentration of NaOCl resulted in the adaptive protection from NaOCl killing and also provided cross-protection from H2O2 killing. Taken together, the results suggest that the toxicity of NaOCl is partially mediated by the generation of peroxides and other reactive oxygen species that are removed by primary peroxide scavenging enzymes, such as catalases and AhpC, as a part of an overall strategy that protects the bacteria from the lethal effects of NaOCl.

Oxidative stress response in Pseudomonas putida

Pseudomonas putida is widely distributed in nature and is capable of degrading various organic compounds due to its high metabolic versatility. The survival capacity of P. putida stems from its frequent exposure to various endogenous and exogenous oxidative stresses. Oxidative stress is an unavoidable consequence of interactions with various reactive oxygen species (ROS)-inducing agents existing in various niches. ROS could facilitate the evolution of bacteria by mutating genomes. Aerobic bacteria maintain defense mechanisms against oxidative stress throughout their evolution. To overcome the detrimental effects of oxidative stress, P. putida has developed defensive cellular systems involving induction of stress-sensing proteins and detoxification enzymes as well as regulation of oxidative stress response networks. Genetic responses to oxidative stress in P. putida differ markedly from those observed in Escherichia coli and Salmonella spp. Two major redox-sensing transcriptional regulators, SoxR and OxyR, are present and functional in the genome of P. putida. However, the novel regulators FinR and HexR control many genes belonging to the E. coli SoxR regulon. Oxidative stress can be generated by exposure to antibiotics, and iron homeostasis in P. putida is crucial for bacterial cell survival during treatment with antibiotics. This review highlights and summarizes current knowledge of oxidative stress in P. putida, as a model soil bacterium, together with recent studies from molecular genetics perspectives.

Copper chloride induces antioxidant gene expression but reduces ability to mediate H2O2 toxicity in Xanthomonas campestris

Copper (Cu)-based biocides are currently used as control measures for both fungal and bacterial diseases in agricultural fields. In this communication, we show that exposure of the bacterial plant pathogen Xanthomonas campestris to nonlethal concentrations of Cu2+ ions (75 µM) enhanced expression of genes in OxyR, OhrR and IscR regulons. High levels of catalase, Ohr peroxidase and superoxide dismutase diminished Cu2+-induced gene expression, suggesting that the production of hydrogen peroxide (H2O2) and organic hydroperoxides is responsible for Cu2+-induced gene expression. Despite high expression of antioxidant genes, the CuCl2-treated cells were more susceptible to H2O2 killing treatment than the uninduced cells. This phenotype arose from lowered catalase activity in the CuCl2-pretreated cells. Thus, exposure to a nonlethal dose of Cu2+ renders X. campestris vulnerable to H2O2, even when various genes for peroxide-metabolizing enzymes are highly expressed. Moreover, CuCl2-pretreated cells are sensitive to treatment with the redox cycling drug, menadione. No physiological cross-protection response was observed in CuCl2-treated cells in a subsequent challenge with killing concentrations of an organic hydroperoxide. As H2O2 production is an important initial plant immune response, defects in H2O2 protection are likely to reduce bacterial survival in plant hosts and enhance the usefulness of copper biocides in controlling bacterial pathogens.

Pseudomonas aeruginosa thiol peroxidase protects against hydrogen peroxide toxicity and displays atypical patterns of gene regulation

The Pseudomonas aeruginosa PAO1 thiol peroxidase homolog (Tpx) belongs to a family of enzymes implicated in the removal of toxic peroxides. We have shown the expression of tpx to be highly inducible with redox cycling/superoxide generators and diamide and weakly inducible with organic hydroperoxides and hydrogen peroxide (H(2)O(2)). The PAO1 tpx pattern is unlike the patterns for other peroxide-scavenging genes in P. aeruginosa. Analysis of the tpx promoter reveals the presence of a putative IscR binding site located near the promoter. The tpx expression profiles in PAO1 and the iscR mutant, together with results from gel mobility shift assays showing that purified IscR specifically binds the tpx promoter, support the role of IscR as a transcriptional repressor of tpx that also regulates the oxidant-inducible expression of the gene. Recombinant Tpx has been purified and biochemically characterized. The enzyme catalyzes thioredoxin-dependent peroxidation and can utilize organic hydroperoxides and H(2)O(2) as substrates. The Δtpx mutant demonstrates differential sensitivity to H(2)O(2) only at moderate concentrations (0.5 mM) and not at high (20 mM) concentrations, suggesting a novel protective role of tpx against H(2)O(2) in P. aeruginosa. Altogether, P. aeruginosa tpx is a novel member of the IscR regulon and plays a primary role in protecting the bacteria from submillimolar concentrations of H(2)O(2).

Regulators of oxidative stress response genes in Escherichia coli and their functional conservation in bacteria

Oxidative stress, through the production of reactive oxygen species, is a natural consequence of aerobic metabolism. Escherichia coli has several major regulators activated during oxidative stress, including OxyR, SoxRS, and RpoS. OxyR and SoxR undergo conformation changes when oxidized in the presence of hydrogen peroxide and superoxide radicals, respectively, and subsequently control the expression of cognate genes. In contrast, the RpoS regulon is induced by an increase in RpoS levels. Current knowledge regarding the activation and function of these regulators and their dependent genes in E. coli during oxidative stress forms the scope of this review. Despite the enormous genomic diversity of bacteria, oxidative stress response regulators in E. coli are functionally conserved in a wide range of bacterial groups, possibly reflecting positive selection of these regulators. SoxRS and RpoS homologs are present and respond to oxidative stress in Proteobacteria, and OxyR homologs are present and function in H(2)O(2) resistance in a range of bacteria, from gammaproteobacteria to Actinobacteria. Bacteria have developed complex, adapted gene regulatory responses to oxidative stress, perhaps due to the prevalence of reactive oxygen species produced endogenously through metabolism or due to the necessity of aerotolerance mechanisms in anaerobic bacteria exposed to oxygen.

Novel roles of SoxR, a transcriptional regulator from Xanthomonas campestris, in sensing redox-cycling drugs and regulating a protective gene that have overall implications for bacterial stress physiology and virulence on a host plant

In Xanthomonas campestris pv. campestris, SoxR likely functions as a sensor of redox-cycling drugs and as a transcriptional regulator. Oxidized SoxR binds directly to its target site and activates the expression of xcc0300, a gene that has protective roles against the toxicity of redox-cycling compounds. In addition, SoxR acts as a noninducible repressor of its own expression. X. campestris pv. campestris requires SoxR both for protection against redox-cycling drugs and for full virulence on a host plant. The X. campestris model of the gene regulation and physiological roles of SoxR represents a novel variant of existing bacterial SoxR models.

Evaluation of the virulence of Xanthomonas campestris pv. campestris mutant strains lacking functional genes in the OxyR regulon

Xanthomonas campestris pv. campestris causes black rot in cruciferous crops. Hydrogen peroxide (H(2)O(2)) production and accumulation is an important initial response in plant defense against invading microbes. The role of genes involved in the bacterial H(2)O(2) protection system in pathogenicity was evaluated. Mutants of katA (encoding a monofunctional catalase) and, to a lesser extent, katG (encoding a catalase-peroxidase) and oxyR (encoding a H(2)O(2) sensor and a transcription regulator), are hypersensitive to H(2)O(2) treatments that mimic the plant H(2)O(2) burst. These data correlate with the results of pathogenicity testing that show katA, katG, and oxyR mutants are avirulent on a compatible plant. Moreover, exposure to H(2)O(2) (1, 2, and 4 mM) highly induces the expression of genes in the OxyR regulon, including katA, katG, and ahpC. The avirulent phenotype of the oxyR mutant is partly because of its inability to mount an adaptive response upon exposure to an H(2)O(2) burst. Our data provide insights into important roles of a transcription regulator and other genes involved in peroxide stress protection in the virulence of X. campestris pv. campestris.

Genes for hydrogen peroxide detoxification and adaptation contribute to protection against heat shock in Xanthomonas campestris pv. campestris

Xanthomonas campestris pv. campestris, a soil-borne plant-pathogenic bacterium, is exposed to multiple stresses in the environment and during interaction with a host plant. The roles of hydrogen peroxide (H(2) O(2) )-protective genes (katA, katG, and ahpC) and a peroxide sensor/transcription regulator (oxyR) in the viability of X. campestris pv. campestris at an elevated temperature were evaluated. The single katA and katG mutants showed moderate decreased survival after the heat treatment, while the double katA-katG and oxyR mutants were the most vulnerable to the heat treatment compared with a wild-type strain. However, ahpC provided no protective function against the heat treatment. Flow cytometric analysis revealed an increased accumulation of peroxide in cells treated with heat. Altogether, the data revealed a crucial role of genes in the H(2) O(2) detoxification system for protection against lethal heat shock in X. campestris pv. campestris.

Copper ions potentiate organic hydroperoxide and hydrogen peroxide toxicity through different mechanisms in Xanthomonas campestris pv. campestris

Copper (Cu)-based biocides are important chemical controls for both fungal and bacterial diseases in crop fields. Here, we showed that Cu ions at a concentration of 100 μM enhanced t-butyl hydroperoxide (tBOOH) and hydrogen peroxide (H(2) O(2) ) killing of Xanthomonas campestris pv. campestris through different mechanisms. The addition of an antilipid peroxidation agent (α-tocopherol) and hydroxyl radical scavengers (glycerol and dimethyl sulphoxide) partially protected the bacteria from the Cu-enhanced tBOOH and H(2) O(2) killing, respectively. Inactivation of the alkyl hydroperoxide reductase gene rendered the mutant vulnerable to lethal doses of copper sulphate, which could be alleviated by the addition of an H(2) O(2) scavenger (pyruvate) and α-tocopherol. Taken together, the data suggest that Cu ions influence the killing effect of tBOOH through the stimulation of lipid peroxidation, while hydroxyl radical production is the underlying mechanism responsible for the Cu-ion-enhanced H(2) O(2) killing effects.

The catalase-peroxidase KatG is required for virulence of Xanthomonas campestris pv. campestris in a host plant by providing protection against low levels of H2O2

Xanthomonas campestris pv. campestris katG encodes a catalase-peroxidase that has a role in protecting the bacterium against micromolar concentrations of H(2)O(2). A knockout mutation in katG that causes loss of catalase-peroxidase activity correlates with increased susceptibility to H(2)O(2) and a superoxide generator and is avirulent in a plant model system. katG expression is induced by oxidants in an OxyR-dependent manner.

Mini-Tn7 vectors as genetic tools for gene cloning at a single copy number in an industrially important and phytopathogenic bacteria, Xanthomonas spp

Transposon mini-Tn7 vectors insert into the chromosome of several Gram-negative bacteria in a site-specific manner. Here, we showed the application of mini-Tn7 as single copy site-specific integration vector system for Xanthomonas campestris pv. campestris. The transposition of the mini-Tn7 into the bacterial genome was detected at a Tn7 attachment (attTn7) site located downstream of glmS1. Furthermore, using a newly constructed vector pBBR1FLP2 containing the flipase (FLP) recombinase for site-specific excision of the sequence between the FLP recombinase target (FRT) sites, and a sacB counter selection marker, an unmarked mini-Tn7 insertion mutant was created. Mini-Tn7 insertion did not affect bacterial virulence on the tested plant. The mini-Tn7 and FLP-FRT systems also work well in Xanthomonas oryzae pv. oryzae.

Chromosome-based genetic complementation system for Xylella fastidiosa

Xylella fastidiosa is a xylem-limited, gram-negative bacterium that causes Pierce's disease of grapevine. Here, we describe the construction of four vectors that facilitate the insertion of genes into a neutral site (NS1) in the X. fastidiosa chromosome. These vectors carry a colE1-like (pMB1) replicon and DNA sequences from NS1 flanking a multiple-cloning site and a resistance marker for one of the following antibiotics: chloramphenicol, erythromycin, gentamicin, or kanamycin. In X. fastidiosa, vectors with colE1-like (pMB1) replicons have been found to result primarily in the recovery of double recombinants rather than single recombinants. Thus, the ease of obtaining double recombinants and the stability of the resulting insertions at NS1 in the absence of selective pressure are the major advantages of this system. Based on in vitro and in planta characterizations, strains carrying insertions within NS1 are indistinguishable from wild-type X. fastidiosa in terms of growth rate, biofilm formation, and pathogenicity. To illustrate the usefulness of this system for complementation analysis, we constructed a strain carrying a mutation in the X. fastidiosa cpeB gene, which is predicted to encode a catalase/peroxidase, and showed that the sensitivity of this mutant to hydrogen peroxide could be overcome by the introduction of a wild-type copy of cpeB at NS1. Thus, this chromosome-based complementation system provides a valuable genetic tool for investigating the role of specific genes in X. fastidiosa cell physiology and virulence.

Dual role of OhrR as a repressor and an activator in response to organic hydroperoxides in Streptomyces coelicolor

Organic hydroperoxide resistance in bacteria is achieved primarily through reducing oxidized membrane lipids. The soil-inhabiting aerobic bacterium Streptomyces coelicolor contains three paralogous genes for organic hydroperoxide resistance: ohrA, ohrB, and ohrC. The ohrA gene is transcribed divergently from ohrR, which encodes a putative regulator of MarR family. Both the ohrA and ohrR genes were induced highly by various organic hydroperoxides. The ohrA gene was induced through removal of repression by OhrR, whereas the ohrR gene was induced through activation by OhrR. Reduced OhrR bound to the ohrA-ohrR intergenic region, which contains a central (primary) and two adjacent (secondary) inverted-repeat motifs that overlap with promoter elements. Organic peroxide decreased the binding affinity of OhrR for the primary site, with a concomitant decrease in cooperative binding to the adjacent secondary sites. The single cysteine C28 in OhrR was involved in sensing oxidants, as determined by substitution mutagenesis. The C28S mutant of OhrR bound to the intergenic region without any change in binding affinity in response to organic peroxides. These results lead us to propose a model for the dual action of OhrR as a repressor and an activator in S. coelicolor. Under reduced conditions, OhrR binds cooperatively to the intergenic region, repressing transcription from both genes. Upon oxidation, the binding affinity of OhrR decreases, with a concomitant loss of cooperative binding, which allows RNA polymerase to bind to both the ohrA and ohrR promoters. The loosely bound oxidized OhrR can further activate transcription from the ohrR promoter.

OxyR regulated the expression of two major catalases, KatA and KatB, along with peroxiredoxin, AhpC in Pseudomonas putida

OxyR is known to activate/repress the expression of the oxyR regulon, which consists of several genes, which play important antioxidant role in Escherichia coli. To elucidate the role of OxyR in Pseudomonas putida KT2442, the oxyR1 mutation that caused the upregulation of ahpC in a toluene-resistant variant strain was introduced, because no null mutants in oxyR were isolated. This mutation was shown to cause the accumulation of a catalase (KatA) along with AhpC throughout the growth, and of a RpoS-dependent catalase/peroxidase (KatB) in the stationary phase. Following the identification of the transcription start site of two catalase genes, sequences similar to those involved in the proposed OxyR binding for E. coli were found upstream from each of the promoter regions of katA and katB, as well as ahpC. Purified OxyR was shown to bind to these sequences, under both reduced and oxidized states. Moreover, the oxyR1 mutation increased the transcription levels of these genes. These results are consistent with the conclusion, distinct from those observed in an opportunistic pathogen Pseudomonas aeruginosa, that OxyR controlled expression of all the principal peroxide-degrading enzymes in P. putida. The mutation did not cause any notable changes in the transcriptional levels of several antioxidant genes, including those of glutathione reductase, glutaredoxins and thioredoxins, which would involve maintenance of the cellular thiol-disulfide balance, suggesting that the transcriptional regulation of these antioxidant genes should be different from that of katA, katB and ahpC in P. putida.

Putative lipoproteins identified by bioinformatic genome analysis of Leifsonia xyli ssp. xyli, the causative agent of sugarcane ratoon stunting disease

SUMMARY Leifsonia xyli ssp. xyli is the causative agent of ratoon stunting disease, a major cause of economic loss in sugarcane crops. Understanding of the biology of this pathogen has been hampered by its fastidious growth characteristics in vitro. However, the recent release of a genome sequence for this organism has allowed significant novel insights. Further to this, we have performed a bioinformatic analysis of the lipoproteins encoded in the L. xyli genome. These analyses suggest that lipoproteins represent c. 2.0% of the L. xyli predicted proteome. Functional analyses suggest that lipoproteins make an important contribution to the physiology of the pathogen and may influence its ability to cause disease in planta.

Challenging Xanthomonas campestris with low levels of arsenic mediates cross-protection against oxidant killing

Xanthomonas encounters highly toxic reactive oxygen species (ROS) from many sources, such as those generated by plants against invading bacteria, other soil bacteria and from aerobic respiration. Thus, conditions that alter intracellular ROS levels such as exposure to toxic metalloids would have profound effects on bacterial physiology. Here, we report that exposure of Xanthomonas campestris pv. phaseoli (Xp) to low levels of arsenic induces physiological cross-protection against killing by H(2)O(2) and organic hydroperoxide but not a superoxide generator. Cross-protection against H(2)O(2) and organic hydroperoxide toxicity was due to increased expression of genes encoding major peroxide-metabolizing enzymes such as alkyl hydroperoxide reductase (AhpC), catalase (KatA) and organic hydroperoxide resistance protein (Ohr). Arsenic-induced protection against H(2)O(2) and organic hydroperoxide requires the peroxide stress response regulators, OxyR and OhrR, respectively. Moreover, analyses of double mutants of the major H(2)O(2) and organic hyproperoxide-scavenging enzymes, Xp ahpC katA and Xp ahpC ohr, respectively, suggested the existence of unidentified OxyR- and OhrR-regulated genes that are involved in arsenic-induced resistance to H(2)O(2) and organic hyproperoxide killing in Xp. These arsenic-induced physiological alterations could play an important role in bacterial survival both in the soil environment and during plant-pathogen interactions.

Role of oxyR in the oral anaerobe Porphyromonas gingivalis

Porphyromonas gingivalis is an anaerobic microorganism that inhabits the oral cavity, where oxidative stress represents a constant challenge. A putative transcriptional regulator associated with oxidative stress, an oxyR homologue, is known from the P. gingivalis W83 genome sequence. We used microarrays to characterize the response of P. gingivalis to H2O2 and examine the role of oxyR in the regulation of this response. Most organisms in which oxyR has been investigated are facultative anaerobes or aerobes. In contrast to the OxyR-regulated response of these microorganisms to H2O2, the main feature of the response in P. gingivalis was a concerted up-regulation of insertion sequence elements related to IS1 transposases. Common OxyR-regulated genes such as dps and ahpFC were not positively regulated in P. gingivalis in response to H2O2. However, their expression was dependent on the presence of a functional OxyR, as revealed by microarray comparison of an oxyR mutant to the wild type. Phenotypic characterization of the oxyR mutant showed that OxyR plays a role in both the resistance to H2O2 and the aerotolerance of P. gingivalis. Escherichia coli and other bacteria with more complex respiratory requirements use OxyR for regulating resistance to H2O2 and use a separate regulator for aerotolerance. In P. gingivalis, the presence of a single protein combining the two functions might be related to the comparatively smaller genome size of this anaerobic microorganism. In conclusion, these results suggest that OxyR does not act as a sensor of H2O2 in P. gingivalis but constitutively activates transcription of oxidative-stress-related genes under anaerobic growth.

Analysis of mutations that alter HO sensing and transcription regulation properties of a global peroxide regulator OxyR in Xanthomonas campestris pv. phaseoli

OxyR5, from a Xanthomonas campestris pv. phaseoli H(2)O(2)-resistant mutant, contains the two mutations G197D and L301R. The protein exists in its oxidized-like form in the absence of oxidants as judged by the protein's ability to activate the ahpC promoter. Analysis of DNase I footprint patterns indicates that under reducing conditions OxyR5 and OxyRG197D bind to the target site in the ahpC promoter in a manner similar to oxidized wild-type OxyR. Site-directed mutagenesis showed that OxyR5 behaves like oxidized OxyR, independent of the highly conserved C residues at positions 199 and 208 where, in normal OxyR, a disulfide bond between these residues converts the protein from its reduced to the oxidized form. The presence of aspartic acid or valine residue at position 197 caused OxyR to behave like the oxidized form in uninduced cells. Changing D197 to A or T in OxyR5 resulted in proteins with similar properties to native OxyR. In vivo, OxyR5 probably locked in an oxidized-like conformation, resulting in continuous high-level activation of target genes in the OxyR regulon.

OxyR mediated compensatory expression between ahpC and katA and the significance of ahpC in protection from hydrogen peroxide in Xanthomonas campestris

katA and ahpC, encoding monofunctional catalase and alkyl hydroperoxide reductase, respectively, play important protective roles against peroxide toxicity in Xanthomonas campestris pv. phaseoli (Xp). The expression of both katA and ahpC is controlled by the global peroxide sensor and transcriptional activator, OxyR. In Xp, these two genes have compensatory expression patterns. Inactivation of katA leads to an increase in the level of AhpC and a concomitant increase in resistance to tert-butyl hydroperoxide (tBOOH). High-level expression of katA from an expression vector in Xp also lowered the level of ahpC expression. The compensatory regulation of katA and ahpC was mediated by OxyR, since the compensatory response was not observed in an oxyR mutant background. ahpC and katA play important but unequal roles in protecting Xp from H(2)O(2) toxicity. These observations, taken together with a previous observation that an ahpC mutant expresses high levels of KatA and is hyper-resistant to H(2)O(2), suggest the possibility that inactivation of either gene leads to accumulation of intracellular H(2)O(2). This in turn oxidizes reduced OxyR and converts the regulator to the oxidized form that then activates expression of genes in the OxyR regulon.

Important role for methionine sulfoxide reductase in the oxidative stress response of Xanthomonas campestris pv. phaseoli

A methionine sulfoxide reductase gene (msrA) from Xanthomonas campestris pv. phaseoli has unique expression patterns and physiological function. msrA expression is growth dependent and is highly induced by exposure to oxidants and N-ethylmaleimide in an OxyR- and OhrR-independent manner. An msrA mutant showed increased sensitivity to oxidants but only during stationary phase.