title: Defence of Rhizobium etli bacteroids against oxidative stress involves a complexly regulated atypical 2-Cys peroxiredoxin.
abstract: In general, oxidative stress, the consequence of an aerobic lifestyle, induces bacterial antioxidant defence enzymes. Here we report on a peroxiredoxin of Rhizobium etli, prxS, strongly expressed under microaerobic conditions and during the symbiotic interaction with Phaseolus vulgaris. The microaerobic induction of the prxS-rpoN2 operon is mediated by the alternative sigma factor RpoN and the enhancer-binding protein NifA. The RpoN-dependent promoter is also active under low-nitrogen conditions through the enhancer-binding protein NtrC. An additional symbiosis-specific weak promoter is located between prxS and rpoN2. Constitutive expression of prxS confers enhanced survival and growth to R. etli in the presence of H2O2. Single prxS mutants are not affected in their symbiotic abilities or defence response against oxidative stress under free-living conditions. In contrast, a prxS katG double mutant has a significantly reduced (>40%) nitrogen fixation capacity, suggesting a functional redundancy between PrxS and KatG, a bifunctional catalase-peroxidase. In vitro assays demonstrate the reduction of PrxS protein by DTT and thioredoxin. PrxS displays substrate specificity towards H2O2 (Km = 62 microM) over alkyl hydroperoxides (Km > 1 mM). Peroxidase activity is abolished in both the peroxidatic (C56) and resolving (C156) cysteine PrxS mutants, while the conserved C81 residue is required for proper folding of the protein. Resolving of the R. etli PrxS peroxidatic cysteine is probably an intramolecular process and intra- and intersubunit associations were observed. Taken together, our data support, for the first time, a role for an atypical 2-Cys peroxiredoxin against oxidative stress in R. etli bacteroids.
authors.affiliation: Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium.
authors.forename: Bruno
authors.initials: B
authors.lastname: Dombrecht
authors.forename: Christophe
authors.initials: C
authors.lastname: Heusdens
authors.forename: Serge
authors.initials: S
authors.lastname: Beullens
authors.forename: Christel
authors.initials: C
authors.lastname: Verreth
authors.forename: Esther
authors.initials: E
authors.lastname: Mulkers
authors.forename: Paul
authors.initials: P
authors.lastname: Proost
authors.forename: Jos
authors.initials: J
authors.lastname: Vanderleyden
authors.forename: Jan
authors.initials: J
authors.lastname: Michiels
mesh_terms: D000332:Aerobiosis; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D017124:Conserved Sequence; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007700:Kinetics; D008969:Molecular Sequence Data; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D010544:Peroxidases / Q000235:genetics*; D042163:Rhizobium etli / Q000187:drug effects / Q000502:physiology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D006861:Hydrogen Peroxide; D010544:Peroxidases