An iron-regulated alkyl hydroperoxide reductase (AhpC) confers aerotolerance and oxidative stress resistance to the microaerophilic pathogen Campylobacter jejuni

Microaerophiles like Campylobacter jejuni must resist oxidative stresses du ring transmission or Infection. Growth of C, jejuni 81116 under iron limita tion greatly increased the expression of two polypeptides of 26 and 55 kDa, The identification of these proteins by N-terminal amino acid sequencing s howed both to be involved in the defense against oxidative stress. The 55-k Da polypeptide was identical to C. jejuni catalase (KatA), whereas the N te rminus of the 26-kDa polypeptide was homologous to a 26-kDa Helicobacter py lori protein, The gene encoding the C. jejuni 26-kDa protein was cloned, an d the encoded protein showed significant homology to the small subunit of a lkyl hydroperoxide reductase (AhpC), The upstream region of ahpC encoded a divergent ferredoxin (fdxA) homolog, whereas downstream sequences contained flhB and motB homologs, which are involved in flagellar motility, There wa s no evidence for an adjacent homolog of ahpF, encoding the large subunit o f alkyl hydroperoxide reductase, Reporter gene studies showed that iron reg ulation of ahpC and katA is achieved at the transcriptional level. Insertio nal mutagenesis of the ahpC gene resulted in an increased sensitivity to ox idative stresses caused by cumene hydroperoxide and exposure to atmospheric oxygen, while resistance to hydrogen peroxide was not affected, The C, jej uni AhpC protein is an important determinant of the ability of this microae rophilic pathogen to survive oxidative and aerobic stress.