2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 55-9
Presentation Time: 3:30 PM


ONSTOTT, Tullis1, LAU, C.Y.M.2, MAGNABOSCO, Cara2, SLATER, Greg F.3, SHERWOOD LOLLAR, Barbara4, KIEFT, Thomas5, STEPANAUSKAS, Ramunas6, VAN HEERDEN, Esta7 and BORGONIE, G.8, (1)Geosciences, Princeton University, Guyot Hall, Washington Rd, Princeton, NJ 08540, (2)Department of Geosciences, Princeton University, Princeton, NJ 08544, (3)School of Geography and Earth Sciences, McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1, Canada, (4)Department of Geology, University of Toronto, 22 Russell Street, Toronto, ON M5S 3B1, Canada, (5)Dept. of Biology, New Mexico Tech, Albequerque, NM 87801, (6)Single Cell Genomics Center, Bigelow Laboratory for Ocean Sciences, East Boothbay, ME 04544, (7)Dept. of Biotechnology, University of Free State, P.O. Box 339, Bloemfontein, 9300, South Africa, (8)Department of Biology, Nematology Section, Ghent University, Ledeganckstraat 35, Ghent, B9000, Belgium, tullis@princeton.edu

A compilation of cellular abundances from over 150 publications on continental subsurface microbiology suggests that the continental subsurface biomass is comprised of ~1016-17 grams of carbon. Although the cellular abundance diminishes with depth, the trend is punctuated with numerous spikes in concentrations related to geochemical interfaces. The fraction of this biomass that is metabolically active also varies. Next generation sequencing has revealed some variation in the microbial community structure between different subsurface sites, but also detects a core of shared phyla. In these environments the energetically efficient acetyl-CoA pathway for carbon fixation plays a central role for chemolithoautotrophic primary producers that form the base of the biomass pyramid. Nitrogen cycling and fixation is an active process and appears essential to the subsurface biosphere. These primary producers appear to be sustained indefinitely by H2 generated through a host of water/rock reactions. Carbon isotope data suggest that in some subsurface locations the disproportionately abundant secondary consumers are sustained by the primary production of biogenic CH4 from a much smaller population of methanogens. 14C analyses indicate that the in situ CH4 turnover rates are as high as 100 nanomolar/year in organic-poor fractured rock environments. Interactions between prokaryotes and viruses may be fundamental to evolutionary processes and to the biomass concentration. It is widely recognized that the subsurface biosphere alters the composition of groundwater and hydrocarbons. During the tectonic cycle the host rock units will reside within the habitable zone of the subsurface biosphere for millions to billions of years. The subsurface biosphere alters of the host rock texture at scales ranging from the tens of microns to hundreds of meters. Thus, the impact of subsurface microbial activity on rock texture, chemistry and isotopic composition warrants closer scrutiny.