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Published Online March 29, 2001
Science DOI: 10.1126/science.1058332

Reports

Submitted on December 15, 2000
Accepted on March 20, 2001

C-Dead Living Biomass: Evidence for Microbial Assimilation of Ancient Organic Carbon During Shale Weathering

S. T. Petsch 1*, T. I. Eglinton 1, K. J. Edwards 1

1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.

* To whom correspondence should be addressed. E-mail: spetsch{at}whoi.edu.

Prokaryotes have been cultured from a modern weathering profile developed on a ~365-million-year-old black shale that use macromolecular shale organic matter as their sole organic carbon source. Using natural abundance 14C analysis of membrane lipids, we show that 74 to 94% of lipid carbon in these cultures derives from assimilation of 14C-free organic carbon from the shale. These results reveal that microorganisms enriched from shale weathering profiles are able to utilize a macromolecular and putatively refractory pool of ancient organic matter. This activity may facilitate the oxidation of sedimentary organic matter to inorganic carbon when sedimentary rocks are exposed by erosion. Thus, microorganisms may play a more active role in the geochemical carbon cycle than previously recognized, with profound implications for controls on the abundance of O2 and CO2 in Earth's atmosphere over geologic time.


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