The Microbiology of Sulfate-Methane Interfaces in Anoxic SedimentsEPA Grant Number: F6E21122
Title: The Microbiology of Sulfate-Methane Interfaces in Anoxic Sediments
Investigators: Lloyd, Karen G.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Carleton, James N
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $101,212
RFA: STAR Graduate Fellowships (2006) RFA Text | Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Marine Microbiology
A natural constraint on the release of the greenhouse gas methane from marine sediments into the atmosphere is the anaerobic oxidation of methane (AOM). This process is important in many marine settings, however the microbes driving AOM have only been studied in methane seeps. I propose to compare the communities responsible for AOM in Gulf of Mexico methane seeps, where methane fluxes are high, to AOM communities in the White Oak River, NC, a coastal estuary with a slow flux of biogenic methane. I will also determine whether communities responsible for methane destruction switch to methane production due to environmental shifts.
A) How do the composition and quantity of the microbial groups responsible for AOM differ between high flux methane seeps and more globally prevalent low methane flux coastal sediments? Is there a threshold methane flux needed to support these populations?
B) Do organisms responsible for AOM switch to methane production when sulfate is no longer available for AOM? Initially, are these microbes still active below the zone of AOM? If so, does their biomass stable isotope composition reflect a carbon source of methane or the standard substrates of methanogenesis (CO2, acetate, formate)?
I will assess microbial communities at these sites using sequences of 16S rRNA and functional genes that are present in the microbes responsible for AOM and methanogenesis. I will then quantify these organisms through catalyzed reporter deposition in situ fluorescent hybridization (CARD-FISH) and quantitative PCR (qPCR). To determine a direct link between these organisms and their carbon source (methane for AOM and carbon dioxide or acetate for methanogenesis), I will use RNA magnetic bead capture and stable isotope probing to determine the δ13C of RNA of specific organisms.
Preliminary results suggest that similar microbial community compositions are present at both high and low methane flux sites, but abundances will probably differ. ANMEs appear to remain active well below the zone of AOM, suggesting that they may play a role in methanogenesis, a process that has been hypothesized in these microbes, but not yet observed. If this is true, I expect to find that their δ13C matches that of methanogenic substrates. Understanding the metabolic flexibility of these organisms will be essential for predicting responses of AOM-associated communities to environmental perturbations in a wider range of marine environments.