Methanogenic Degradation of Long n -Alkanes Requires Fumarate-Dependent Activation

Methanogenic degradation of -alkanes is prevalent in -alkane-impacted anoxic oil reservoirs and oil-polluted sites. However, little is known about the initial activation mechanism of the substrate, especially -alkanes with a chain length above C16. Here, a methanogenic C-C -alkane-degrading enrichment culture was established from production water of a low-temperature oil reservoir. At the end of the incubation (364 days) C to C (1-methylalkyl)succinates were detected in the -alkane-amended enrichment culture, suggesting that fumarate addition had occurred in the degradation process. This evidence is supported further by the positive amplification of the gene encoding the alpha subunit of alkylsuccinate synthase. A phylogenetic analysis shows these amplicons to be affiliated with and clades. Together with the high abundance of these clades in the bacterial community, these two species are postulated to be the key players in the degradation of C-C -alkanes in the current study. Our results provide evidence that long -alkanes are activated via a fumarate addition mechanism under methanogenic conditions.Methanogenic hydrocarbon degradation is the major process for oil degradation in subsurface oil reservoirs and is blamed for the formation of heavy oil and oil sands. Addition of -alkanes to fumarate yielding alkyl-substituted succinates is a well characterized anaerobic activation mechanism for hydrocarbons and is the most common activation mechanism in anaerobic biodegradation of -alkanes with chain length less than C16. However, the activation mechanism involved in the methanogenic biodegradation of -alkanes longer than C16 is still uncertain. In this study we analyzed a methanogenic enrichment culture amended with a mixture of C to C -alkanes. These -alkanes can be activated via fumarate addition by mixed cultures containing and species under methanogenic conditions. These observations provide fundamental understanding of long -alkanes metabolism under methanogenic condition and have important applications for the remediation of oil-contaminated sites and for energy recovery from oil reservoirs.