In situ detection of anaerobic alkane metabolites in subsurface environments

Abstract

Alkanes comprise a substantial fraction of crude oil and refined fuels. As such, they are prevalent within deep subsurface fossil fuel deposits and in shallow subsurface environments such as aquifers that are contaminated with hydrocarbons. These environments are typically anaerobic, and host diverse microbial communities that can potentially use alkanes as substrates. Anaerobic alkane biodegradation has been reported to occur under nitrate-reducing, sulfate-reducing, and methanogenic conditions. Elucidating the pathways of anaerobic alkane metabolism has been of interest in order to understand how microbes can be used to remediate contaminated sites. Alkane activation primarily occurs by addition to fumarate, yielding alkylsuccinates, unique anaerobic metabolites that can be used to indicate in situ anaerobic alkane metabolism. These metabolites have been detected in hydrocarbon-contaminated shallow aquifers, offering strong evidence for intrinsic anaerobic bioremediation. Recently, studies have also revealed that alkylsuccinates are present in oil and coal seam production waters, indicating that anaerobic microbial communities can utilize alkanes in these deeper subsurface environments. In many crude oil reservoirs, the in situ anaerobic metabolism of hydrocarbons such as alkanes may be contributing to modern-day detrimental effects such as oilfield souring, or may lead to more beneficial technologies such as enhanced energy recovery from mature oilfields. In this review, we briefly describe the key metabolic pathways for anaerobic alkane (including n-alkanes, isoalkanes, and cyclic alkanes) metabolism and highlight several field reports wherein alkylsuccinates have provided evidence for anaerobic in situ alkane metabolism in shallow and deep subsurface environments.

Comparative analysis of metagenomes from three methanogenic hydrocarbon-degrading enrichment cultures with 41 environmental samples

“…In contrast, members of the Deltaproteobacteria, particularly Syntrophus/Smithella sp., have been implicated in methanogenic alkane degradation, particularly of longer-chain alkanes (Zengler et al, 1999;Gray et al, 2011;Cheng et al, 2013). Indeed, all of the known strictly anaerobic (for example, sulfate-reducing/syntrophic) alkane degraders are Deltaproteobacteria (Mbadinga et al, 2011;Agrawal and Gieg, 2013;Callaghan, 2013). However, the implication of a Peptococcaceae in degradation of low molecular weight n-alkanes (for example, propane) under sulfate-reducing conditions (Kniemeyer et al, 2007) and iso-alkanes under methanogenic conditions (Abu Laban et al, in press; Tan et al, 2014B) supports a role for Firmicutes in anaerobic alkane degradation.…”

Metabolism of Hydrocarbons in <b><i>n</i></b>-Alkane-Utilizing Anaerobic Bacteria

“…Using quantum chemical calculations, it has been shown that this reaction is exothermic and has an overall energy change around -40 kJ/mol [Beasley and Nanny, 2012]. Accordingly, n -alkylsuccinates (including methylsuccinate) occasionally detected in hydrocarboncontaining natural environments have been attributed to the terminal activation of n -alkanes [Agrawal and Gieg, 2013;Gieg et al, 2010].…”

Microbial enzymes that oxidize hydrocarbons

“…Among recent discoveries are new mechanisms and enzymes involved in anaerobic alkane oxidation. In this issue, we have included review articles by Callaghan (2013) and Agrawal and Gieg (2013) outlining the current state of knowledge regarding anaerobic methane and non-methane alkane oxidation and methods for the in situ detection of anaerobic alkane biodegradation.…”