Fumarate metabolism and the microaerophily of Campylobacter species

(1) The role of fumarate metabolism in the microaerophily of the Campylobacter genus and the effects of therapeutic agents against it were investigated. (2) NMR spectroscopy was employed to determine the properties of Campylobacter fumarase (Fum) and fumarate reductase (Frd). Radiotracer analysis was used to determine the production of carbon dioxide by Campylobacter cells. Standard microbiological techniques were used to measure the effects of environmental conditions and inhibitors on bacterial growth. (3) All Campylobacter species tested showed both Fum and Frd activities. Frd activity was observed with or without the addition of an exogenous electron donor in the particulate fractions obtained from lysates. Fumarate was oxidized to carbon dioxide via the acetyl-CoA cleavage pathway. The genes encoding proteins involved in fumarate metabolism were identified in the Campylobacter jejuni genome. Cells grew better in atmospheres with 5 and 10% oxygen levels. Fum activity was the same in cultures grown under different oxygen tensions and did not vary with the age of cultures. Frd activity was higher in cultures which grew at faster rates and decreased with the age of cultures. Four Frd inhibitors showed bactericidal effects against Campylobacter spp. with different potencies. The relative strengths of inhibition of the compounds followed the same order as the bactericidal effects. (4) The results suggested that Frd and Fum are constitutive and play a fundamental role in these microaerophiles which show characteristics of anaerobic metabolism, and that the Frd inhibitors tested would not be of therapeutic use.