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From the Cover
PHYSICAL SCIENCES / BIOLOGICAL SCIENCES / GEOLOGY / MICROBIOLOGY
Fossil genes and microbes in the oldest ice on Earth

Kay D. Bidle^*, SangHoon Lee^*,, David R. Marchant, and Paul G. Falkowski^*,,¶

*Environmental Biophysics and Molecular Ecology Program, Institute of Marine and Coastal Sciences, and Department of Geological Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901; Polar Research Institute, Korea Ocean Research and Development Institute, Incheon 406-840, Korea; and Department of Earth Sciences, Boston University, Boston, MA 02215

Edited by David M. Karl, University of Hawaii, Honolulu, HI, and approved June 26, 2007 (received for review March 9, 2007)

Although the vast majority of ice that formed on the Antarctic continent over the past 34 million years has been lost to the oceans, pockets of ancient ice persist in the Dry Valleys of the Transantarctic Mountains. Here we report on the potential metabolic activity of microbes and the state of community DNA in ice derived from Mullins and upper Beacon Valleys. The minimum age of the former is 100 ka, whereas that of the latter is 8 Ma, making it the oldest known ice on Earth. In both samples, radiolabeled substrates were incorporated into macromolecules, and microbes grew in nutrient-enriched meltwaters, but metabolic activity and cell viability were critically compromised with age. Although a 16S rDNA-based community reconstruction suggested relatively low bacterial sequence diversity in both ice samples, metagenomic analyses of community DNA revealed many diverse orthologs to extant metabolic genes. Analyses of five ice samples, spanning the last 8 million years in this region, demonstrated an exponential decline in the average community DNA size with a half-life of 1.1 million years, thereby constraining the geological preservation of microbes in icy environments and the possible exchange of genetic material to the oceans.

ancient ice | community DNA | metabolism | metagenomic analysis | cosmic radiation

Author contributions: K.D.B. and S.L. contributed equally to this work; K.D.B., S.L., and P.G.F. designed research; K.D.B. and S.L. performed research; K.D.B., S.L., and D.R.M. contributed new reagents/analytic tools; K.D.B., S.L., D.R.M., and P.G.F. analyzed data; and K.D.B., S.L., D.R.M., and P.G.F. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. ER915562–ER916102; ER916113; EF127594–EF127627).

This article contains supporting information online at www.pnas.org/cgi/content/full/0702196104/DC1.

^¶To whom correspondence should be addressed. E-mail: falko{at}marine.rutgers.edu

© 2007 by The National Academy of Sciences of the USA

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PNAS 2007 104: 13211-13212. [Full Text]