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Quantifying Microbial Utilization of Petroleum Hydrocarbons in Salt Marsh Sediments by Using the ¹³C Content of Bacterial rRNA

Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, Massachusetts 02138,¹ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125,² Department of Biological Sciences, University of Southern California, Los Angeles, California 90089³

Received 6 May 2007/ Accepted 4 December 2007

Natural remediation of oil spills is catalyzed by complex microbial consortia. Here we took a whole-community approach to investigate bacterial incorporation of petroleum hydrocarbons from a simulated oil spill. We utilized the natural difference in carbon isotopic abundance between a salt marsh ecosystem supported by the ¹³C-enriched C₄ grass Spartina alterniflora and ¹³C-depleted petroleum to monitor changes in the ¹³C content of biomass. Magnetic bead capture methods for selective recovery of bacterial RNA were used to monitor the ¹³C content of bacterial biomass during a 2-week experiment. The data show that by the end of the experiment, up to 26% of bacterial biomass was derived from consumption of the freshly spilled oil. The results contrast with the inertness of a nearby relict spill, which occurred in 1969 in West Falmouth, MA. Sequences of 16S rRNA genes from our experimental samples also were consistent with previous reports suggesting the importance of Gamma- and Deltaproteobacteria and Firmicutes in the remineralization of hydrocarbons. The magnetic bead capture approach makes it possible to quantify uptake of petroleum hydrocarbons by microbes in situ. Although employed here at the domain level, RNA capture procedures can be highly specific. The same strategy could be used with genus-level specificity, something which is not currently possible using the ¹³C content of biomarker lipids.

Published ahead of print on 14 December 2007.