Identification of a non‐haem catalase in Salmonella and its regulation by RpoS (σ^S)

Abstract

We report the identification and functional analysis of katN, a gene encoding a non‐haem catalase of Salmonella enterica serotype Typhimurium. katN, which is not present in Escherichia coli, is located between the yciGFE and yciD E. coli homologues in the Salmonella genome. Its predicted protein product has a molecular weight of 31 826 Da and is similar to the Mn‐catalases of Lactobacillus plantarum and Thermus spp. Its product, KatN, was visualized as a 37 kDa protein in E. coli maxicells. A KatN recombinant protein, containing six histidine residues at its C‐terminus, was purified, and its catalase activity was observed on a non‐denaturing polyacrylamide gel. KatN was also visualized by catalase activity gel staining of bacterial cell extracts. Its expression was shown to be regulated by growth phase and rpoS. Northern blotting indicated that kat forms an operon with the upstream yciGFE genes. A putative rpoS‐regulated promoter was identified upstream of yciG. Southern blotting revealed that katN is conserved within Salmonella serovars. katN homologues were found in Pseudomonas aeruginosa, Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae and Serratia marcescens. A katN mutation did not appear to affect the hydrogen peroxide (H2O2) response of Salmonella. However, the expression of katN increased the H2O2 resistance of unadapted cells in the exponential phase and of rpoS mutants in stationary phase. Thus, KatN may contribute to hydrogen peroxide resistance in Salmonella in certain environmental conditions.

Characterization of the RpoS Status of Clinical Isolates of Salmonella enterica

“…In particular, rpoS mutants are impaired in the ability to resist hydrogen peroxide (H 2 O 2 ) during the stationary phase. Indeed, two of the three catalases produced by Salmonella are expressed in the stationary phase under the control of rpoS; these are KatE and KatN, a major catalase and a minor catalase, respectively (4,35). Therefore, to obtain further information on the presence of rpoS mutant alleles, we carried out a semiquantitative visual examination of S expression in these strains by adding H 2 O 2 to the bacterial colony mass derived from a nutrient agar plate.…”

Regulation ofSalmonella entericaSerovar TyphimuriummntHTranscription by H2O2, Fe2+, and Mn2+

“…Second, the MntR gene stop codon overlaps the start codon of the gene encoding putative membrane protein YbiR, b0818 in Blattner E. coli notation (6), whose BLAST hits are annotated variously as carboxylate or arsenate transporters. We are investigating the possibility that YbiR mediates the Mn 2ϩ efflux activity that we observed during our characterization of MntH as an Mn 2ϩ uptake protein (24 (36), and the orthologous protein phosphatases PrpA and PrpB (28,29,39), which modulate repair of envelope damage in E. coli. Metabolic Mn 2ϩ enzymes include ppGpp synthase/hydrolase SpoT, which modulates the bacterial response to amino acid starvation (12,30,37) and phosphoglyceromutase YibO, b3612 in Blattner E. coli notation (6), which is regulated distinctly from the 2,3-bisphosphoglycerate-cofactored GpmA (14,17) and for which a distinctive role is not yet known.…”

Transcriptional Regulation ofsitABCDofSalmonella entericaSerovar Typhimurium by MntR and Fur

“…The importance of Mn in the biology of prokaryotic cell function is only beginning to be appreciated (21). Mn is required for several enzymes involved in general metabolism but is also required for oxidative stress response proteins, including the superoxide dismutase SodA and the nonheme catalase KatN (33). Indeed, SodA is predicted to be the predominant enzyme containing Mn in the cell.…”