Exploring microbial sulphate reduction under high temperature and pressure

• Applicant: Dr. Jens Kallmeyer
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 408249062

Even in deep sediment layers under several kilometers of sediments there are active microorganisms. Temperature increases with depth and eventually exceeds the limit to which life is possible. So far the upper limit of life was found to be around 120° C. It was found in microorganisms from hydrothermal systems, the so-called Black Smokers. In sediments however the upper temperature limit appears to be much lower. Data from oilfields indicate a limit around 80° C. The discrepancy between hydrothermal and sedimentary systems was explained by the fact that microorganisms cannot gain enough energy in sedimentary systems to carry out the repair of their biomolecules like proteins and DNA at higher temperatures. Interestingly, the proof of metabolic activity at very high temperatures in the lab is only possible when the experiments are carried out at high pressure. IODP Expedition 370 was specifically designed to solve the question of the upper temperature limit of life in sedimentary systems. In the Nankai Trough off the coast of Japan the geothermal gradient is around 100° C/km, which means that the entire temperature range of life stretches over a depth interval of slightly more than one kilometre. By using the most advanced drilling and laboratory techniques it was possible to obtain absolutely pristine samples that are devoid of any contamination. The expedition had a highly interdisciplinary character so that a multitude of biological and chemical parameter was measured, allowing a very detailed characterization of the sediment. The proposed project is an important component of the expedition because sulphate reduction is the quantitatively most important anaerobic process for degradation of organic matter in the seabed. Within the framework of an MSc thesis first measurements of sulphate reduction rates were already carried out and they proved that this process does indeed occur over the entire cored depth interval, albeit at very low rates. As part of the proposed project more measurements are planned, also under high pressure conditions. In order to achieve this a high pressure thermal gradient system shall be constructed and operated. Additional to sediments from Nankai Trough we plan for experiments with hydrothermally influenced material from Guaymas Basin. Comparison between these to types of sediment will allow deeper understanding of the functioning of one of the most important biological processes in the sea floor and the limits of life in general.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 527: Bereich Infrastruktur - "International Ocean Discovery Program" (IODP)
• Co-Investigator: Professor Dr. Dirk Wagner