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Content archived on 2024-05-27

Development and assessment of new techniques and approaches for detecting deep sub-seafloor bacteria and their interaction with geosphere processes


Problems to be solved
Marine sediments cover 70% of the Earth's surface and contain the largest global reservoir of organic carbon. Surprisingly, high bacterial populations are present to at least hundreds of metres depth (deepest current sample 842 m, oldest 14 mya) in these sediments. These bacteria are not just surviving, they are thriving in the extreme conditions at these depths; they have high diversity and are well adapted to life in the subsurface. Bacterial biomass in these sediments represent ca.10% of the total surface biomass and the sub-seafloor biosphere is a substantial new habitat on Earth. Bacteria probably exist even deeper where they are fuelled by geosphere processes. However, existing microbiological techniques are inadequate for deeper investigation. This project will develop new techniques and approaches for deep biosphere research and these will be tested and refined in deep sediment simulation experiments and by application to future Ocean Drilling Program (ODP) Legs. These procedures will then be used to explore this biosphere's coupling to the geosphere and explore even deeper the frontiers of life in the sub-seafloor.
Scientific objectives and approach
This project involves an interdisciplinary group of microbiologists and organic geochemists to develop methods and approaches to explore the deep biosphere in sub-seafloor sediments. New core handling techniques will be developed for deeper more consolidated sediments. Existing methods used to quantify total bacterial populations (direct microscopy), their rates of activity (using 35S and 14C labelled compounds) and to identify active bacterial populations (incorporation of 13C labelled substrates into bacterial PLFA biomarkers and/or 16S-rRNA) will be optimised for the study of the deep sub-surface. Modified or new methods will be applied to deep sediment samples taken on future ODP legs. Temperature limits for bacterial activities will be determined in thermal gradient experiments. This will enable a greater understanding of how this ecosystem functions at the biosphere: geosphere interface. In addition novel deep bacteria of potential biotechnological application will be isolated. The latest molecular genetic techniques (DGGE) will be applied to these unique samples to obtain a detailed description of their diversity. Molecular probes will also be developed to rapidly identify and isolate novel organisms in mixed cultures and deep sediments. These isolated cultures will undergo biomarker characterisation to enable interpretation of the distribution of biomarker and macromolecular compounds (GC-, MS, TOC Rock-Eval pyrolysis etc.) from deep sediment samples and those from thermal gradient experiments. Bacterial inputs to buried sedimentary organic carbon and their impact on deep organic matter maturation processes, associated with fossil fuel formation, will be assessed, and the interplay between biological and thermogenic processes will be defined.
Expected impacts
New methods and approaches will be developed and tested which will enable the bacterial biosphere in sub-seafloor sediments to be explored to even greater depths. This will enable the depth limits of life on Earth to be more accurately determined and also the amount of living biomass in the subsurface. The energy sources for this subsurface biosphere will be determined, including the possibility of energy being supplied by deep geosphere processes. This coupling between deep biosphere and geosphere processes may enable life to extend to kilometre depths into the subsurface and bacteria may actually catalyse deep processes, previously thought to be abiological, such as fossil fuel formation.

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EU contribution
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Participants (3)