MECHANISM OF BACTERIAL REDUCTION OF SULPHATE AND OF SULPHITE FROM ISOTOPE FRACTIONATION STUDIES

The fractionation of sulphur isotopes in the reduction of sulphate and of sulphite by the bacteria Desulphovibrio desulphuricans has been studied over a wide range of lactate concentration, temperature, electron donor, pH and conditions of growth using resting cell suspensions and cell free extracts of the bacteria. Isotope effects from 5.1 to 23.7%. were found for sulphate reduction and 1.7 to 25.5%. for sulphite reduction, favouring the lighter sulphur isotope (32S). These results are discussed in terms of a reaction mechanism involving several consecutive steps, favouring a small or large isotope effect, competing for control of the rate. Also sulphur isotope distribution patterns reported for various types of marine environment and marine sediment are discussed in terms of these isotope effects. © 1968.