Respiratory energy transduction by membrane fragments of the phytopathogenic bacteria Pseudomonas cichorii and Pseudomonas aptata

Effect of oxygen limitation on the formation of the electron transport system of the phytopathogenic fluorescent bacterium Pseudomonas cichorii

The composition of the membrane-bound electron transport system of the phytopathogenic bacterium Pseudomonas cichorii underwent modification in response to oxygen supply. Growth adaptation to low oxygen concentrations was characterized by repression of cytochromes involved in ubiquinol-cyt. c oxidoreductase and cyt. c oxidase activities. By contrast, cyto. o, i.e., the alternative cyanide-insensitive oxidase of P. cichorii, was unaffected by low oxygen tension. No a-type cytochromes could be detected at any stage of growth.

Effects of myxothiazol and 5-undecyl-6-hydroxy-4,7-dioxobenzothiazole on the respiratory pathways of the phytopathogenic fluorescent bacteria Pseudomonas cichorii and Pseudomonas aptata

Myxothiazol inhibited the electron transport in the cytochrome b/c segment of membrane particles from Pseudomonas cichorii. A residual NADH-oxidation due to the presence of an alternative pathway via cytochrome o (Em, 7 = +250 mV) was sensitive to the quinone analog 5-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT). This latter inhibitor was equally effective in blocking the linear respiratory chain of Pseudomonas aptata, a strain deficient in cytochromes of c type and Rieske iron-sulphur centre. The analysis of the oxido-reduction kinetic patterns of cytochromes indicated that, among the b type haems present in P. aptata, only cyt. o could be reduced by ubiquinol-1 in a reaction insensitive to both antimycin A and myxothiazol but inhibited by UHDBT. This latter finding has been correlated to the fact that P. aptata exhibits a defective b/c complex. In membranes from P. cichorii, in which the absorption maximum of dithionite reduced cytochrome(s) b shifted by 2-3 nm in the presence of antimycin A and/or myxothiazol, the electron flow through the b/c oxidoreductase complex has tentatively been arranged in a proton motive "Q-cycle" like mechanism.