T.C. ONSTOTT

Deptartment of Geosciences, Princeton University, Princeton, NJ 08544
phone: 609-258-6898 fax: 609-258-1274 e-mail: tullis@princeton.edu http://geo.princeton.edu/research/geomicrobio

Deep Subsurface Microbiology and Astrobiology

Over the past decade analyses of rock cores and groundwater have identified the presence of a subsurface biosphere that mitigates many of the geochemical processes long thought to be abiotic. The existence of this biosphere has significant implications for groundwater quality, remediation of contaminated aquifers, degradation of petroleum reservoirs, CO2 subsurface sequestration and the search for life beneath the surface of Mars and other planetary bodies. During the course of our South African LExEn project we collected ~200 samples of these environments, which are from fluid filled fractures within rocks hundeds of meters beneath the surface. These samples are limited to water emanating from a borehole.   Just how representative these bulk water samples are of the in situ conditions within these fractures is a source of speculation and can only be addressed by probing these fractures directly.

Borehole logging has a long history in the petroleum industry as the standard means of characterizing subsurface structure. More recently, borehole imaging tools, such as video cameras and radar, and borehole probes for pH, Eh, velocity and conductivity are becoming widely used in geophysical and hydrological studies. Voltametric sensors have recently become available for measuring trace metals in ocean water and boreholes.  

In the coming year we plan to develop the first borehole probe for the detection, sampling and analyses of specific enzymes utilized by anaerobic microorganisms. The probe will employ a multi-wavelength spectrometer and photomultiplier fitted for fluorescent measurements. It will be designed to function at pressures up to 200 bars and temperatures up to 60 degrees C. The probe will be designed to collect fluorescent data on fracture surfaces and from fluid samples. The latter will require development of a sampling tool for extracting fluid samples from these fractures zones and pumping the fluid into fluorescent analysis chamber. We will utilize a bioluminescent based detection system as this affords the greatest sensitivity for what will be low biomass/low activity samples. Firefly luciferase will be used to assay ATP and the bacterial luciferase reaction will be used assay for and NAD(P)H. We will also test the feasibility of using a fluorescent assay for quantification of the thiol biomarker coenzyme M (CoM), which is known to be present in all methanogenic bacteria. We will adapt a commercial borehole probe designed to measure the pH, Eh, conductivity, pressure and temperature at depth. We also propose to develop a cassette filtration system for recovering biomass for molecular analyses. This will employ a high pressure circulating pump connected to the fluid sampler and a modified, commercially available, bulk water borehole sampler.  

As a continuation of our South Africa deep microbiology project we are proposing to instrument two boreholes that cut across active fault zones. In collaboration with our South African colleagues we will monitor these boreholes for two years during which we anticipate several magnitude 3-4 earthquakes.   These experiments will provide the first observation regarding the role of seismicity in enhancing nutrient fluxes to subsurface microbial communities as well as the role, if any, played by microorganisms in the nucleation of seismic events.  

As part of our recently awarded Astrobiology Center, we will begin field work in mines located in the Canadian Arctic where permafrost is currently ~500 meters think and overlie brine-bearing Precambrian rocks. Such sites provide an environment more analogous to that of the Martian subsurface and provide an interesting contrast to our much warmer South African subsurface environments. We will thus be able to directly assess the role of temperature on microbial activity. We also hope that with help from the department and the university we will be able to initiate an Astrobiology program for undergraduates that will attract students to the natural sciences.

Recent Publications:

2006 Onstott, T. C., McGown, D., Kessler, J., Sherwood Lollar, B., Lehmann, K. K. and Clifford, S. Martian CH4: sources, flux and detection. Astrobiology Journal 6:377-395.

2006 Lihung, L.-H., Wang, P-L, Rumble, D., Lippmann-Pipke, J., Boice, E., Pratt, L. M., Sherwood Lollar, B., Brodie, Eoin, Hazen, T., Andersen, G., DeSantis, T., Moser, D. P., Kershaw, D. and Onstott, T. C. Long term biosustainability in a high energy, low diversity crustal biotome. Science 314:479-482 (pdf).

2002 Dong H., Onstott, T.C., DeFlaun, M.F., Streger, S.H., Rothmel, R.K. and Mailloux, B.J., Relative Dominance of Physical vs. Chemical Effects on the Transport of Adhesion Deficient Bacteria in Intact Cores from South Oyster, Va., Environ. Science & Tech. 36:891-900 .

2002 Dong, H., Onstott, T.C., Ko., C.H., Elimelech, M., Hollingsworth, A.D., DeFlaun, M.F., Brown, D.G. and Mailloux, B.J.   Theoretical Prediction of Collision Efficiency Between an Adhesion-Deficient Bacterium and Aquifer Sediments. Colloids and Surfaces B: Biointerfaces, 24:229-245.

2002 Dong, H., Rothmel, R., Onstott, T.C., Fuller, M.E., DeFlaun, M.F., Streger, S.H., Dunlap, R., and Fletcher, M. Simultaneous Transport of Two Bacterial Strains in Intact Cores from Oyster, Virginia: Biological Effects and Numerical Modeling. Applied and Environmental Microbiology 68:2120-2132.

2003 Baker, B.J., Moser, D.P., MacGregor, B.J., Fishbain, S., Wagner, M., Fry, N.K., Jackson, B., Speolstra, N., Loos, S., Takai, K., S herwood -L ollar , B., Fredrickson, J.K., Balkwill, D. L., Onstott, T.C., Wimpee, C.F. and Stahl, D.A., Related Assemblages of Sulfate-reducing Bacteria Associated with Ultradeep Gold Mines of South Africa and Deep Basalt Aquifers of Washington State, Environmental Microbiology, 5, 2.

2003 Omar, G., Onstott, T.C. and Hoek, J., The Origin of Deep Subsurface Microbial Communities in the Witwatersrand Basin, South Africa as Deduced from Apatite Fission Track Analyses, Geofluids, 3, 69-80.