Unravelling the sulphur cycle of marine sediments

Abstract

In this invited paper, I give a personal description of my start as a young scientist studying the sulphur cycle of marine sediments. The initial objective was to quantify the processes experimentally using 35S as a tracer. The results showed an unexpected large contribution of sulphate reduction to the oxidation of sediment organic matter. This implied that sulphate reducing bacteria can perform complete oxidation of their substrates to CO2. A quantification of sulphate reducing bacteria compared to measured rates of sulphate reduction revealed that the viable counting techniques available at the time vastly underestimated the true cell numbers. Through our introduction of microsensors for oxygen, sulphide and pH, the microbial oxidation of H2S could be analysed at high spatial resolution. Studies of the large, filamentous sulphur bacteria revealed surprising adaptations to sulphide oxidation based on anaerobic respiration with nitrate stored in vacuoles.