Influence of fluids from the ocean crust on growth and activity of deep-biosphere populations (IODP Leg 301)

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The sediment column of IODP Site 1301 of the eastern flank of the Juan de Fuca Ridge (water depth: 2650 m, sediment coverage: 265 m) is characterised by a diffusive flow of hydrothermal fluids from the underlying ocean crust, a steep temperature gradient of 0.23 °C/m and two sulfate-methane transition zones. One goal of our project is to understand the role of fluids as a driving force for the marine deep biosphere by introducing electron acceptors to deeply buried sediments. This hypothesis was supported by cell quantification and activity measurements along the sediment column. Elevated cell numbers at the sediment-basement interface gave the first evidence for a microbial community stimulated by crustal fluids. Potential phosphatase activity was enhanced in phosphate-depleted layers towards the sediment-basement interface. Rates of sulfate reduction and anaerobic oxidation of methane were elevated within the lower sulfate-methane transition zone. Further investigations are focussed on isolation and characterisation of indigenous microorganisms. Molecular screening, used to determine the microbial composition of enrichment cultures from all sediment layers, revealed different phylotypes. However, as we are dealing with slowly growing prokaryotes, they need up to six months to form a colony. Therefore, the isolation and characterisation of new isolates and the preparation of publications will be finished until the end of the application period.