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Project Progress

Members of our team at UNC Chapel Hill focus on molecular studies of deep subsurface communities. In year 7, we published the first molecular community analyses (16S rRNA genes) of organic-poor deep marine subsurface sediments. In collaboration with MBL team members, we also undertook what may be the first rRNA analyses of deep subsurface communities. These analyses allow us to identify the active members of deep subsurface communities (in contrast to DNA-based assays that combine signatures of active, inactive and dead prokaryotes). Our DNA-based studies of formation fluid from a sealed borehole near Costa Rica indicate that the fluid helps to support a diverse, partially chemolithotrophic community.

The WHOI members of our team continued research on biomarkers and subseafloor processes. With PSU team member C. House, we showed that archaeal communities in deeply buried sulfate-methane transition zones are dominated by two novel lineages that are distinct from methanotrophs in surface sediments and, unlike near-surface methanotrophs, do not assimilate carbon from methane. To further test our Year 6 hypothesis of microbial ethanogenesis and propanogenesis in subseafloor sediments, we are searching for potential abiotic pathways of hydrocarbon formation. We also undertook molecular isotopic studies of peridotite-based hydrothermal ecosystems with abundant chemolithoautotrophs. To date, we have also systematically identified biomarkers that distinguish more than 100 cultures of prokaryotes that collectively cover all major phyla of Bacteria and Archaea.

Members of our team at URI continued to develop and apply techniques for quantification of deep subsurface activities and ecosystem structure. We showed that a deep subseafloor ecosystem is a thermodynamic homeostat where sulfate reduction, iron reduction, methanogenesis and possibly methanotrophy are mutually dependent and produce biologically useful energy throughout a sediment column deposited over millions of years. We are refining our extremely sensitive tritium-based method for detection of life and applying it to deep subseafloor sediments and (in collaboration with IPTAI team members) to deep gold mine samples. We developed and tested (1) a robust new method for determination of subsurface methane concentrations, and (2) techniques for isolation of intact cells from sediments. Future application of the latter techniques will greatly improve analyses of subsurface life.

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