Fine-Scale Control of Microbial Communities in Deep Marine Sediments that Contain Hydrates and High Concentrations of Methane

Authors: Colwell, F. (speaker, Oregon State University), Hangsterfer, A., Brodie, E., Daly, R., Holland, M., Briggs, B., Carini, P., Torres, M., Kastner, M., Long, P., Schaef, H., Delwiche, M., Winters, W., and Riedel, M.

Venue: American Geophysical Union’s fall meeting in San Francisco, CA, December 10–14, 2007 (http://www.agu.org/meetings/fm07/ [external site]).

Abstract: Deep subseafloor sediments with high concentrations of organic carbon and microbially generated methane contain microbial communities that play an important role in the biogeochemical cycling of carbon. However, there remains a limited understanding of the fine (centimeter)-scale sediment properties (e.g., grain size, presence/absence of hydrates) that determine key microbial attributes in deep marine sediments. This project’s objective is to determine the quantity, diversity, and distribution of microbial communities in the context of abiotic properties in gas-rich marine sediments. DNA was extracted from deep marine sediments cored from various continental shelf locations, including offshore India and the Cascadia Margin. Abiotic characterization of the same sediments included grain size analysis, chloride concentrations in sediment pore waters, and presence of hydrates in the sediments as determined by thermal anomalies. As in past studies of such systems, most of the samples yielded low levels of DNA (0.3-1.5 ng/g of sediment). Bacterial DNA appeared to be more easily amplified than archaeal DNA. Initial attempts to amplify DNA using primers specific for the methanogen functional gene, methyl-CoM-reductase, were unsuccessful. Infrequently, cores from relatively shallow sediments (e.g., 0.5 mbsf Leg 204, 1251B-1H) from central (Hydrate Ridge) and northern (offshore Vancouver Island) Cascadia and from India’s eastern margin contained macroscopically visible, pigmented biofilms. One of these biofilms was composed of high concentrations of cell clusters when viewed microscopically. The predominant cells in the Hydrate Ridge biofilm were large (ca. 10 um) cocci, and preliminary characterization of the 16S rDNA amplified and sequenced from this biofilm suggests the prevalence of a microbe with 97% similarity to mycobacteria. These discrete biofilm communities appear to be distinctive relative to the normally sparse distribution of cells in the sediments. By determining how the abiotic properties of deep marine sediments control the numbers and distribution of microbial communities that process organic matter, project researchers hope to provide better parameters for computational models that describe carbon cycling in these systems.

Related NETL Project
The proposed research of the related NETL project FWP-FLU5A425, “Methanogenesis in Hydrate-Bearing Sediments: Integration of Experimental and Theoretical Approaches,” is to improve the understanding of processes that control the distribution, occurrence, and behavior of gas hydrate systems over time, especially with respect to the role played by these systems in global climate change.

NETL Project Contacts
NETL – Robert Vagnetti (robert.vagnetti@netl.doe.gov or 304-285-1334)
Idaho National Laboratory – Mark Delwiche (mark.delwiche@inl.gov or 208-526-1870)
OSU – Rick Colwell (rcolwell@coas.oregonstate.edu or 541-737-5220)