Measurements of Photosynthetic Sulfide Oxidation byChlorobiumUsing a Sulfide Ion Selective Electrode

摘要

A simple technique is described for using a sulfide sensitive electrode to measure the photooxidation of H2S by a green sulfur bacterium,Chlorobium limicolaformathiosulfatophilum. Sulfide photooxidation occurred only in the presence of bicarbonate at concentrations greater than 0.1 mM. This implies that the rate-limiting carboxylating enzyme for CO2fixation inChlorobiumhas a relatively low affinity for CO2compared to ribulose-1,5-biphosphate carboxylase. Carbonyl cyanide-p-trifluoromethoxyphenyl-hydrazone (FCCP), an uncoupler of photophosphorylation, delays sulfide oxidation for about 15 sec after the onset of illumination at 2μM and is completely inhibitory at 10μM. These effects can be explained by the ATP requirement for CO2fixation. When the photooxidation of H2S was prevented by 10μM FCCP, a photoevolution of H2S was observ