Quantifying microbial utilization of petroleum hydrocarbons in salt-marsh sediments using the ^(13)C content of bacterial rRNA

Abstract

Natural remediation of oil spills is catalyzed by complex microbial consortia. Here we take 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 ^(13)C-enriched C4 grass, Spartina alterniflora, and the ^(13)C-depleted composition of petroleum to monitor changes in the ^(13)C content of biomass. Magnetic-bead capture methods for the selective recovery of bacterial RNA were used to monitor the ^(13)C content of bacterial biomass during a two-week experiment. The data show that by the end of the experiment, up to 26% of bacterial biomass 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 {delta}-Proteobacteria 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 ^(13)C content of biomarker lipids.

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