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

The energy transduction by respiratory membranes from the fluorescent phytopathogenic bacteria Pseudomonas cichorii and Pseudomonas aptata has been examined. Both species have shown to perform ATP synthesis linked to oxidation of NADH with P/2e^- ratios ranging between 0.25 and 0.42. This phosphorylation activity is largely insensitive to antimycin A (10^-6 M) and KCN (5·10^-6 M) in membranes from P. aptata, a strain deficient in c type complement (Zannoni 1982). In contrast, the phosphorylation efficiency is partially lowered by antimycin A and KCN in P. cichorii a strain containing a branched respiratory chain (Zannoni 1982). Oxidation of NADH by ubiquinone-1 (UQ-1) in antimycin A-treated membranes from these two pseudomonads is not coupled to ATP generation. This finding indicates that both strains contain a nonenergy conserving membrane-bound NADH dehydrogenase.The location of the sites of energy conservation was investigated by respiratory-induced quenching of the fluorescence of atebrine. This approach has confirmed the P/2e^--ratios measurements along with indication of a energy conserving step at the UQ/cyt. b levels of both bacterial strains. This study has also shown that the cytochrome c oxidase activity by P. cichorii is linked to a proton gradient generation which in turn drives ATP synthesis (P/2e^-=0.1). Previous data indicated that a high-potential cytochrome of b type (cyt. b380, Em_7.0=+380 mV) is involved in the cytochrome c oxidase activity of P. cichorii (Zannoni 1982). The possibility that this bacterial strain is endowed with a terminal b type oxidase operating with a proton pump mechanism is therefore suggested.