4 years ago

Methanogenic paraffin biodegradation: alkylsuccinate synthase gene quantification and dicarboxylic acid production.

Lisa M Gieg, Lisa K Oberding
Paraffinic n-alkanes (> C17) that are solid at ambient temperature comprise a large fraction of many crude oils. The comparatively low water solubility and reactivity of these long-chain alkanes can lead to their persistence in the environment following fuel spills, and pose serious problems for crude oil recovery operations by clogging oil production wells. However, the degradation of waxy paraffins under the anoxic conditions characterizing contaminated groundwater environments and deep subsurface energy reservoirs is poorly understood. Here, we assessed the ability for a methanogenic culture enriched from freshwater fuel-contaminated aquifer sediments to biodegrade the model paraffin n-octacosane (C28H58). Compared to controls, the consumption of n-octacosane was coupled to methane production, demonstrating its biodegradation under these conditions. Smithella was postulated to be an important C28H58 degrader in the culture based on its high relative abundance as determined by 16S rRNA gene sequencing. An identified assA gene (known to encode the α subunit of alkylsuccinate synthase) aligned most closely with those from other Smithella qPCR and reverse transcription qPCR assays based upon assA demonstrated a significant increase in abundance and expression of this gene in C28H58-degrading cultures compared to controls, suggesting n-octacosane activation by fumarate addition. Metabolite analysis revealed the presence of several long chain α, ω-dicarboxylic acids only in the C28H58-degrading cultures, a novel observation providing clues as to how methanogenic consortia access waxy hydrocarbons. The results of this study broaden our understanding of how waxy paraffins can be biodegraded in anoxic environments with application towards bioremediation and improved oil recovery.IMPORTANCE Understanding the methanogenic biodegradation of different classes of hydrocarbons has important applications for effective fuel-contaminated site remediation and for improved recovery from oil reservoirs. Previous studies have clearly demonstrated that short-chain alkanes (C17) that comprise many fuel mixtures. Using an enrichment culture derived from a freshwater fuel-contaminated site, we demonstrate that the model waxy alkane n-octacosane can be biodegraded under methanogenic conditions by a presumed Smithella phylotype. Compared to controls, we show an increased abundance and expression of the assA gene that is known to be important for anaerobic n-alkane metabolism. Metabolite analyses revealed the presence of a range of α, ω-dicarboxylic acids found only in n-octacosane-degrading cultures, a novel finding that lends insight as to how anaerobic communities may access waxes as growth substrates in anoxic environments.

Publisher URL: http://doi.org/10.1128/AEM.01773-17

DOI: 10.1128/AEM.01773-17

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