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Project Progress

To explore the taxonomic composition of subseafloor ecosystems, URI team members finished a 16S ribosomal ribonucleic acid (rRNA) sequencing survey for bacteria and archaea in subseafloor sediments of the Nankai Trough (Kormas et al., 2003) and are working on genetic studies of subseafloor sediments from the Ocean Drilling Program (ODP) Leg 201 (in the Peru Margin and the eastern equatorial Pacific). Lloyd, Lever and Teske are working to isolate, polymerase chain reaction (PCR) amplify, clone and sequence diagnostic key genes for methanogens and sulfate reducers from Leg 201 samples. Lauer, Soerenson and Teske are developing deoxyribonucleic acid (DNA) isolation procedures and documenting bacterial and archaeal 16S rRNA profiles from the Leg 201 samples, using Denaturing Gradient Gel Electrophoresis (DGGE). Initial results of the DGGE analyses show distinct archaeal community differences with depth at the two organic-poor sites we have focused on, ODP Sites 1225 and 1231.

URI team members have also made significant headway toward documenting signatures of present and past microbial processes. Hinrichs, Sturt, K. Smith and Summons’ analyses of intact polar lipids from microbial isolates demonstrate great potential to distinguish microbial phylotypes in natural samples on a species level. Additionally, their studies of Leg 201 samples show that concentrations of intact polar lipids in the deep subsurface are generally orders of magnitude lower than in surface sediments, reflective of significantly lower densities of microbial populations. Hayes, Hinrichs and Hmelo are actively developing protocols for isotopic analysis of volatile fatty acids in subseafloor pore waters. Hinrichs, Bach, Hmelo and Sturt are undertaking mechanistic studies of biological hydrocarbon formation in the deep subsurface (Hinrichs et al., 2003).

URI team members are also advancing understanding of subseafloor microbial activity and its effect on Earth’s biogeochemical cycles. To assess relationships between cell counts and community activity, D. Smith, Chen and Staroscik developed protocols for adenosine triphosphate (ATP) analysis of subseafloor sediments and completed ATP analyses of ODP Site 1230. Rutherford, D’Hondt and Spivack mapped global patterns of subseafloor sulfate reduction and estimated their effect on the global sulfur cycle (Rutherford et al., 2003). Wang, Rutherford, D’Hondt and Spivack are using chemical data and biogeochemical flux models to estimate net rates of several metabolic processes in subseafloor sediments (D’Hondt et al., 2003; Wang et al., 2003).

Some results of these Year 4 studies are provided in the “Highlights” section of this report.