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 the
C. 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
ahpC
encoded a divergent ferredoxin (
fdxA
) homolog, whereas downstream sequences contained
flhB
and
motB
homologs, 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 the
ahpC
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. The
C. jejuni
AhpC protein is an important determinant of the ability of this microaerophilic pathogen to survive oxidative and aerobic stress.