Transient Oxygen Exposure Causes Profound and Lasting Changes to a Benzene-Degrading Methanogenic Community

Area of Science:

• Environmental microbiology
• Bioremediation
• Anaerobic digestion

Background:

• Strictly anaerobic microbial communities are crucial for degrading pollutants like benzene in contaminated environments.
• Methanogenic benzene degradation, carried out by specific bacteria and archaea, is a key process in anoxic environments.
• Understanding the sensitivity of these communities to oxygen is vital for effective bioremediation strategies.

Purpose of the Study:

• To investigate the impact of oxygen exposure on a long-term anaerobic, methanogenic benzene-degrading enrichment culture.
• To determine the tolerance limits of anaerobic benzene degraders to oxygen.
• To compare anaerobic benzene degradation pathways with aerobic ones.

Main Methods:

• Culturing of a benzene-degrading enrichment from oil-contaminated sediment, containing Deltaproteobacteria (ORM2) and methanogenic archaea.
• Controlled introduction of air (oxygen) into batch cultures to simulate leaks.
• Monitoring of benzene degradation rates, microbial community composition (including aerobic and anaerobic taxa), and methanogenesis.

Main Results:

• A small air injection had minimal impact, but a larger injection stalled methanogenesis and perturbed the community.
• A benzene-degrading Pseudomonas species proliferated, consuming oxygen, while anaerobic benzene degrader ORM2 populations declined.
• Recovery of anaerobic benzene degradation and methanogenesis took nearly a year, highlighting the culture's oxygen sensitivity.

Conclusions:

• The studied methanogenic benzene degradation is oxygen-sensitive and fundamentally distinct from aerobic pathways.
• Anaerobic benzene biotransformation is mediated by specific microbial communities, sensitive to oxygen intrusion.
• Microbial decay dynamics are important considerations for modeling mixed microbial communities in environmental settings.