Natural anaerobic degradation of methane and petroleum in marine sediments: geochemical gradients, degradation succession and microbial zonation

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Petroleum is a complex mixture of hydrocarbons and other organic substances. Amongst the hydrocarbons, alkanes, cycloalkanes, and various aromatic compounds make up a large fraction. In the marine environment, petroleum naturally migrates through sediments from deeper reservoirs, passing different redox levels, electron acceptors and zones of microbial degradation processes. Thereby degradable carbon compounds enter the microbially active zone from the energetically lower end of the redox cascade, i.e., from the reduced zone, in opposite to oil spills that settle from the water column, i.e., from the oxygenated top. Consequently, the order of natural petroleum degradation in sediments starts with anaerobic processes through the utilization of different electron acceptors 'in reverse order' and ends with aerobic respiration. Given this flow direction, we expect the natural degradation succession of petroleum components to differ from conventional lab experimentations that concentrate on the degradation ability of selected organisms or enrichment cultures. The main objective of this project is to investigate the succession of microbial petroleum degradation in intact sediment cores from different marine locations simulating both situations: petroleum seepage from below and oil spill from top of the sediment. In addition, the performance of anaerobic oxidation of methane in the presence of petroleum will be explored. Geochemical and molecular methods will be applied to resolve the step-wise vertical degradation of petroleum and to identify the responsible microorganism.