The microaerophilic, catalase-negative, gram-negative
bacterium Campylobacter mucosalis was grown
microaerobically with either hydrogen or formate as electron
donor. A model is proposed for the respiratory adaptation of
the organism to falling oxygen tensions during growth. During
the early stages of growth, when the oxygen concentration is
relatively high, the oxidation of formate is a two-stage
branched process involving hydrogen peroxide production and
its peroxidative removal. In later stages of growth, when the
oxygen concentration is lower as a result of cellular
respiration, the principal electron flow is linear to a
membrane-bound cytochrome-c oxidase which reduces oxygen
directly to water. The reactivity of cytochrome c-553 with the
soluble peroxidase and the membrane-bound cytochrome-c oxidase
was consistent with this cytochrome operating as physiological
electron donor to both enzyme systems.
The cytochrome-c peroxidase was partially purified and
some of its properties determined. The cytochrome-c oxidase
and formate oxidase were both membrane-bound and exhibited a
high affinity for oxygen.
Hydrogen peroxide was produced during the oxidation of
formate, and accumulated when electron flow to the
cytochrome-c peroxidase was inhibited. The capacity for
hydrogen peroxide production was shown to be higher in young
cells. The levels of cytochrome c-553 and of the peroxidase
were higher in cells harvested earlier in growth. In cells
harvested later in growth, the levels of cytochrome-c oxidase
increased and the levels of c-553 decreased.
A proton gradient with lower external pH was developed
with either hydrogen or formate as electron donor, and either
oxygen or hydrogen peroxide as the terminal electron acceptor.
A respiratory role for hydrogen peroxide in this
catalase-negative organism was proposed and discussed in
relation to its microaerophilic nature.
Haem-stained SDS-PAGE gels was one of the methods used to
quantify cytochrome c-553. This method was shown to be
generally applicable to the quantification of c-type
cytochromes and to be useful during investigations into the
induction and location of bacterial cytochromes-c.