Utilization of 35S-thiosulphate and an appraisal of the role of ATP-sulphurylase in chemolithotrophic Thiobacillus ferrooxidans.

Differentially labelled 35S-thiosulphate was taken up by washed cells of Thiobacillus ferrooxidans which were previously grown on thiosulphate. The uptake was proportional to the biomass over the range 0.5-4.0 mg dry wt. of bacteria and showed typical saturation kinetics with an estimated Km value of 0.5 mM for 35S-thiosulphate. Dithionate and Group VI anions inhibited the uptake, which was under pH control and had a temperature optimum of 50 degrees C. In the absence of thiosulphate, the cells bound 35S-sulphate but the binding did not increase on prolonged incubation and the label could be removed completely by washing with dilute sulphuric acid. Increasing amounts of the label were incorporated from [outer-35S]thiosulphate into cellular materials over a 60-min period, whereas little or no assimilation was observed from either the [inner-35S]thiosulphate or 35S-sulphate. The kinetic properties of the sulphate-activating enzyme ATP-sulphurylase enriched from bacteria grown with either thiosulphate or ferrous-iron were similar although this enzyme has an assimilatory function only when the bacterium is grown with ferrous-iron.