The influence of acetate on the oxidation of sulfide by Rhodopseudomonas capsulata

The capacity to oxidize sulfide and the influence of the simultaneous presence of acetate in heterotrophically (acetate) and autotrophically (sulfide/CO₂) grown Rhodopseudomonas capsulata was investigated.Sulfide oxidation of acetate-limited cultures was found inversely related to the specific growth rate. Upon acetate deprevation (metering pump stopped) increased rates of sulfide oxidation were observed. This points to the existence of a constitutive acceptor for the electrons from sulfide. It is suggested that a carrier functional in the light-induced cyclic electron flow operates as such. The rate of sulfide oxidation, however, is low when compared to autotrophically-grown cells. This is probably due to the low levels of Calvin cycle enzymes present in the acetate-grown cells.In cells growing on sulfide/CO₂, the addition of acetate resulted in less sulfide being oxidized. Upon depletion of the acetate, the rate of sulfide oxidation again increased, however, insufficiently to maintain the accelerated growth rate. This indicates that under mixotrophic conditions the enzymes of the Calvin cycle are being synthesized to a far lesser extent.Non-Standurd Abbreviations PHB poly--hydroxybutyric acid - D dilution rate - TCA Tri carboxylic acid cycle - RubPcase ribulose 1,5-bisphosphate carboxylase - RP reducing power