Conversion of crude oil to methane by a microbial consortium enriched from oil reservoir production waters.

Carolina Berdugo-Clavijo,Lisa M Gieg

doi:10.3389/fmicb.2014.00197

Abstract

The methanogenic biodegradation of crude oil is an important process occurring in petroleum reservoirs and other oil-containing environments such as contaminated aquifers. In this process, syntrophic bacteria degrade hydrocarbon substrates to products such as acetate, and/or H2 and CO2 that are then used by methanogens to produce methane in a thermodynamically dependent manner. We enriched a methanogenic crude oil-degrading consortium from production waters sampled from a low temperature heavy oil reservoir. Alkylsuccinates indicative of fumarate addition to C5 and C6 n-alkanes were identified in the culture (above levels found in controls), corresponding to the detection of an alkyl succinate synthase encoding gene (assA/masA) in the culture. In addition, the enrichment culture was tested for its ability to produce methane from residual oil in a sandstone-packed column system simulating a mature field. Methane production rates of up to 5.8 μmol CH4/g of oil/day were measured in the column system. Amounts of produced methane were in relatively good agreement with hydrocarbon loss showing depletion of more than 50% of saturate and aromatic hydrocarbons. Microbial community analysis revealed that the enrichment culture was dominated by members of the genus Smithella, Methanosaeta, and Methanoculleus. However, a shift in microbial community occurred following incubation of the enrichment in the sandstone columns. Here, Methanobacterium sp. were most abundant, as were bacterial members of the genus Pseudomonas and other known biofilm forming organisms. Our findings show that microorganisms enriched from petroleum reservoir waters can bioconvert crude oil components to methane both planktonically and in sandstone-packed columns as test systems. Further, the results suggest that different organisms may contribute to oil biodegradation within different phases (e.g., planktonic vs. sessile) within a subsurface crude oil reservoir.

Highlights

In hydrocarbon-impacted subsurface environments, fuel components can be anaerobically biodegraded via a number of anaerobic electron accepting processes including nitrate, iron, and sulfate reduction (Widdel et al, 2010)
A crude oil-degrading enrichment culture was established from production waters of a heavy oil reservoir
The microbial community sampled from the residual oil column was dominated by members of DISCUSSION In this work, a methanogenic consortium enriched from production waters of a low-temperature oil reservoir was found to be capable of utilizing hydrocarbon components in crude oil

Summary

Introduction

In hydrocarbon-impacted subsurface environments, fuel components can be anaerobically biodegraded via a number of anaerobic electron accepting processes including nitrate, iron, and sulfate reduction (Widdel et al, 2010). Addition to fumarate as an initial hydrocarbon activation mechanism under anoxic conditions was initially demonstrated with toluene under nitrate-reducing conditions (Biegert et al, 1996) and subsequently for other alkyl-substituted monoaromatic compounds (reviewed in Foght, 2008; Widdel et al, 2010). N-alkanes were shown to be activated via addition to fumarate by nitrate- and sulfate-reducing bacteria (e.g., Kropp et al, 2000; Rabus et al, 2001; Callaghan et al, 2006). Fumarate addition genes (e.g., ass/mas for alkanes or bss for toluene) have been identified in methanogenic oil-degrading enrichments (Zhou et al, 2012; Aitken et al, 2013; Tan et al, 2013) and samples from www.frontiersin.org

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