Methanogenic biodegradation of two-ringed polycyclic aromatic hydrocarbons

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Subsurface science

Background:

• Polycyclic aromatic hydrocarbons (PAH) are prevalent in subsurface environments.
• Biodegradation pathways of PAH under methanogenic conditions are poorly understood.
• Methane-rich environments like oil reservoirs and aquifers are key areas for PAH contamination.

Purpose of the Study:

• To investigate the methanogenic biodegradation of specific PAH compounds.
• To identify the microbial communities involved in PAH metabolism under anaerobic conditions.
• To assess the potential for bioremediation of PAH-contaminated sites.

Main Methods:

• Enrichment culture of crude oil-degrading methanogens.
• Incubation with naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, and 2,6-dimethylnaphthalene.
• Methane production measurements and metabolite analysis (e.g., naphthoic acids).
• Microbial community analysis using 454 pyrosequencing.

Main Results:

• Significant methane production observed with 2-methylnaphthalene and 2,6-dimethylnaphthalene, correlating with stoichiometric predictions.
• Naphthalene and 1-methylnaphthalene showed minimal biodegradation.
• Formation of 2-naphthoic acid and 6-methyl-2-naphthoic acid confirmed metabolism of substituted naphthalenes.
• Enrichments were dominated by Methanosaeta, Methanoculleus (Archaea), and Clostridiaceae (Bacteria).

Conclusions:

• Specific substituted naphthalenes can be biodegraded under methanogenic conditions.
• Methanogenic archaea and specific bacterial groups are key players in this process.
• Findings provide insights into PAH fate in anaerobic subsurface environments and potential bioremediation strategies.