AUTHOR=Berdugo-Clavijo Carolina , Gieg Lisa M. 

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

JOURNAL=Frontiers in Microbiology

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2014.00197

DOI=10.3389/fmicb.2014.00197

ISSN=1664-302X

ABSTRACT=<p>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 H<sub>2</sub> and CO<sub>2</sub> 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 C<sub>5</sub> and C<sub>6</sub><italic>n</italic>-alkanes were identified in the culture (above levels found in controls), corresponding to the detection of an alkyl succinate synthase encoding gene (<italic>assA/masA</italic>) 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 CH<sub>4</sub>/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 <italic>Smithella, Methanosaeta</italic>, and <italic>Methanoculleus</italic>. However, a shift in microbial community occurred following incubation of the enrichment in the sandstone columns. Here, <italic>Methanobacterium</italic> sp. were most abundant, as were bacterial members of the genus <italic>Pseudomonas</italic> 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.</p>