Abstract
Expression of the peroxide stress genes alkyl hydroperoxide reductase (
ahpC
) and catalase (
katA
) of the microaerophile
Campylobacter jejuni
is repressed by iron. Whereas iron repression in gram-negative bacteria is usually carried out by the Fur protein, previous work showed that this is not the case in
C. jejuni
, as these genes are still iron repressed in a
C. jejuni fur
mutant. An open reading frame encoding a Fur homolog (designated PerR for “peroxide stress regulator”) was identified in the genome sequence of
C. jejuni
. The
perR
gene was disrupted by a kanamycin resistance cassette in
C. jejuni
wild-type and
fur
mutant strains. Subsequent characterization of the
C. jejuni perR
mutants showed derepressed expression of both AhpC and KatA at a much higher level than that obtained by iron limitation, suggesting that expression of these genes is controlled by other regulatory factors in addition to the iron level. Other iron-regulated proteins were not affected by the
perR
mutation. The
fur perR
double mutant showed derepressed expression of known iron-repressed genes. Further phenotypic analysis of the
perR
mutant,
fur
mutant, and the
fur perR
double mutant showed that the
perR
mutation made
C. jejuni
hyperresistant to peroxide stress caused by hydrogen peroxide and cumene hydroperoxide, a finding consistent with the high levels of KatA and AhpC expression, and showed that these enzymes were functional. Quantitative analysis of KatA expression showed that both the
perR
mutation and the
fur
mutation had profound effects on catalase activity, suggesting additional non-iron-dependent regulation of KatA and, by inference, AhpC. The PerR protein is a functional but nonhomologous substitution for the OxyR protein, which regulates peroxide stress genes in other gram-negative bacteria. Regulation of peroxide stress genes by a Fur homolog has recently been described for the gram-positive bacterium
Bacillus subtilis. C. jejuni
is the first gram-negative bacterium where non-OxyR regulation of peroxide stress genes has been described and characterized.