Mutation of alkyl hydroperoxide reductase gene ahpC of Xanthomonas oryzae pv. oryzae affects hydrogen peroxide accumulation during the rice–pathogen interaction

ABSTRACT Amphibacillus xylanus and Sporolactobacillus inulinus NADH oxidases belonging to the peroxiredoxin oxidoreductase family show extremely high peroxide reductase activity for hydrogen peroxide and alkyl hydroperoxides in the presence of the small disulfide redox protein, AhpC (peroxiredoxin). In order to investigate the distribution of this enzyme system in bacteria, 15 bacterial strains were selected from typical aerobic, facultatively anaerobic, and anaerobic bacteria. AhpC-linked alkyl hydroperoxide reductase activities were detected in most of the tested strains, and especially high activities were shown in six bacterial species that grow well under aerobic conditions, including aerobic bacteria (Alcaligenes faecalis and Bacillus licheniformis) and facultatively anaerobic bacteria (Amphibacillus xylanus, Sporolactobacillus inulinus, Escherichia coli, andSalmonella enterica serovar Typhimurium). In the absence of AhpC, the purified enzymes from A. xylanus andS. inulinus catalyze the NADH-linked reduction of oxygen to hydrogen peroxide. Similar activities were observed in the cell extracts from each of these six strains. The cell extract of B. licheniformis revealed the highest AhpC-linked alkyl hydroperoxide reductase activity in the four strains, withV max values for hydrogen peroxide and alkyl hydroperoxides being similar to those for the enzymes fromA. xylanus and S. inulinus. Southern blot analysis of the three strains probed with the A. xylanusperoxiredoxin reductase gene revealed single strong bands, which are presumably derived from the individual peroxiredoxin reductase genes. Single bands were also revealed in other strains which show high AhpC-linked reductase activities, suggesting that the NADH oxidases belonging to the peroxiredoxin oxidoreductase family are widely distributed and possibly play an important role both in the peroxide-scavenging systems and in an effective regeneration system for NAD in aerobically growing bacteria.

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Alkyl Hydroperoxide Reductase Is the Primary Scavenger of Endogenous Hydrogen Peroxide in Escherichia coli

Journal of Bacteriology ◽

10.1128/jb.183.24.7173-7181.2001 ◽

2001 ◽

Vol 183 (24) ◽

pp. 7173-7181 ◽

Cited By ~ 501

Author(s):

Lauren Costa Seaver ◽

James A. Imlay

Keyword(s):

Escherichia Coli ◽

Hydrogen Peroxide ◽

Candidate Genes ◽

Residual Activity ◽

Aerobic Metabolism ◽

Scavenging Activity ◽

Wild Type ◽

Alkyl Hydroperoxide Reductase ◽

E Coli ◽

Alkyl Hydroperoxide

ABSTRACT Hydrogen peroxide is generated during aerobic metabolism and is capable of damaging critical biomolecules. However, mutants ofEscherichia coli that are devoid of catalase typically exhibit no adverse phenotypes during growth in aerobic media. We discovered that catalase mutants retain the ability to rapidly scavenge H2O2 whether it is formed internally or provided exogenously. Analysis of candidate genes revealed that the residual activity is due to alkyl hydroperoxide reductase (Ahp). Mutants that lack both Ahp and catalase could not scavenge H2O2. These mutants excreted substantial amounts of H2O2, and they grew poorly in air. Ahp is kinetically a more efficient scavenger of trace H2O2 than is catalase and therefore is likely to be the primary scavenger of endogenous H2O2. Accordingly, mutants that lack Ahp accumulated sufficient hydrogen peroxide to induce the OxyR regulon, whereas the OxyR regulon remained off in catalase mutants. Catalase still has an important role in wild-type cells, because the activity of Ahp is saturated at a low (10−5 M) concentration of H2O2. In contrast, catalase has a high K m , and it therefore becomes the predominant scavenger when H2O2 concentrations are high. This arrangement is reasonable because the cell cannot provide enough NADH for Ahp to rapidly degrade large amounts of H2O2. In sum,E. coli does indeed generate substantial H2O2, but damage is averted by the scavenging activity of Ahp.

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