Homologous overexpression of alkyl hydroperoxide reductase subunit C (ahpC) protects Bifidobacterium longum strain NCC2705 from oxidative stress

Helicobacter cinaedi, a common human intestinal bacterium, has been implicated in various enteric and systemic diseases in normal and immunocompromised patients. Protection against oxidative stress is a crucial component of bacterium-host interactions. Alkyl hydroperoxide reductase C (AhpC) is an enzyme responsible for detoxification of peroxides and is important in protection from peroxide-induced stress.H. cinaedipossesses a singleahpC, which was investigated with respect to its role in bacterial survival during oxidative stress. TheH. cinaedi ahpCmutant had diminished resistance to organic hydroperoxide toxicity but increased hydrogen peroxide resistance compared with the wild-type (WT) strain. The mutant also exhibited an oxygen-sensitive phenotype and was more susceptible to killing by macrophages than the WT strain.In vivoexperiments in BALB/c and BALB/c interleukin-10 (IL-10)−/−mice revealed that the cecal colonizing ability of theahpCmutant was significantly reduced. The mutant also had diminished ability to induce bacterium-specific immune responsesin vivo, as shown by immunoglobulin (IgG2a and IgG1) serum levels. Collectively, these data suggest thatH. cinaedi ahpCnot only contributes to protecting the organism against oxidative stress but also alters its pathogenic propertiesin vivo.

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An Iron-Regulated Alkyl Hydroperoxide Reductase (AhpC) Confers Aerotolerance and Oxidative Stress Resistance to the Microaerophilic Pathogen Campylobacter jejuni

Journal of Bacteriology ◽

10.1128/jb.181.16.4798-4804.1999 ◽

1999 ◽

Vol 181 (16) ◽

pp. 4798-4804 ◽

Cited By ~ 122

Author(s):

Marie-Louise A. Baillon ◽

Arnoud H. M. van Vliet ◽

Julian M. Ketley ◽

Chrystala Constantinidou ◽

Charles W. Penn

Keyword(s):

Oxidative Stress ◽

Campylobacter Jejuni ◽

Insertional Mutagenesis ◽

Atmospheric Oxygen ◽

Large Subunit ◽

Upstream Region ◽

Transcriptional Level ◽

Alkyl Hydroperoxide Reductase ◽

Oxidative Stresses ◽

Alkyl Hydroperoxide

ABSTRACT Microaerophiles like Campylobacter jejuni must resist oxidative stresses during transmission or infection. Growth of C. jejuni 81116 under iron limitation greatly increased the expression of two polypeptides of 26 and 55 kDa. The identification of these proteins by N-terminal amino acid sequencing showed both to be involved in the defense against oxidative stress. The 55-kDa polypeptide was identical to C. jejuni catalase (KatA), whereas the N terminus of the 26-kDa polypeptide was homologous to a 26-kDa Helicobacter pylori protein. The gene encoding theC. jejuni 26-kDa protein was cloned, and the encoded protein showed significant homology to the small subunit of alkyl hydroperoxide reductase (AhpC). The upstream region of ahpCencoded a divergent ferredoxin (fdxA) homolog, whereas downstream sequences contained flhB and motBhomologs, which are involved in flagellar motility. There was no evidence for an adjacent homolog of ahpF, encoding the large subunit of alkyl hydroperoxide reductase. Reporter gene studies showed that iron regulation of ahpC and katA is achieved at the transcriptional level. Insertional mutagenesis of theahpC gene resulted in an increased sensitivity to oxidative stresses caused by cumene hydroperoxide and exposure to atmospheric oxygen, while resistance to hydrogen peroxide was not affected. TheC. jejuni AhpC protein is an important determinant of the ability of this microaerophilic pathogen to survive oxidative and aerobic stress.

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