Unravelling the sulphur cycle of marine sediments.

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 ³⁵ S 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 CO ₂ . 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 H ₂ S 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.
(© 2019 Society for Applied Microbiology and John Wiley & Sons Ltd.)