ATP formation coupled to caffeate reduction by H₂ in Acetobacterium woodii NZva16

Abstract

We have addressed the question, whether the reduction of caffeate in Acetobacterium woodii strain NZva16 is coupled to ATP synthesis by electron transport phosphorylation. The following results were obtained: 1. Cultures of A. woodii with H₂ and CO₂, grew to greater cell densities, when caffeate was also present. Caffeate was reduced to give hydrocaffeate and less acetate was formed. The cell yield based on the amount of caffeate reduced was approximately 1 g dry cells/mol. 2. Non-growing bacterial suspensions catalyzed the reduction of caffeate by H₂. The specific activity (0.2–1.0 μmol · min⁻¹ · mg⁻¹ bacterial protein) was as high as expected for a catabolic reaction. 3. The ATP content of bacteria incubated, with H₂ increased from < 1 to about 7 μmol per g cellular protein on the addition of caffeate. The ATP yield was calculated as 0.06 mol ATP · mol⁻¹ caffeate from the initial velocity of ATP formation and the activity of caffeate reduction. Valinomycin together with nigericin inhibited ATP formation and caused a 2–3-fold increase of the activity of caffeate reduction. Protonophores were without, effect. 4. Caffeate in the presence of H₂ caused the uptake of tetraphenylphosphonium cation by the bacteria. The uptake was abolished by valinomycin plus nigericin, and was considerably enhanced by monensin. Protonophores were without effect, even in the presence of monensin. It is concluded that caffeate reduction by H₂ is coupled to ATP formation by electron transport phosphorylation. However, the failure of protonophores to prevent phosphorylation and TPP uptake cannot be explained.