Methanogen Oxygen Stress: An Investigation of the Superoxide Dismutase Gene

Methanogenesis is a major metabolic pathway long associated with strictly anaerobic conditions predominantly due in part to the high sensitivity of obligate methanogenic archaea to oxygen toxicity. However, there is increasing evidence that methanogenic archaea can survive prolonged periods of oxygen stress in both pure culture and environmental conditions. The molecular defense mechanisms against oxygen stress in strict anaerobic microbes is unclear but there is mounting genomic evidence that complex antioxidative defense enzymes associated with aerobes may play a major role. The effect of oxygen stress on methanogenesis production, the presence/absence of the SOD gene, and Archaea community structure was investigated using a soil slurry incubation experiment with inoculum from two Trunk River soil types. The growth of archeal communities was approximated by measuring methane production rates from incubation serum vials. DNA was extracted for SOD analysis and TOPO cloning at regular intervals before and after oxygen stress to determine any subsequent shift in the archeal microbial population or SOD gene expression. It was found that methane production was reduced significantly after oxygen stress but returned to near control levels when reduced conditions were reestablished. Lastly, SOD was detected in meso-enrichment cultures, as well as, the positive methanogenic control and is likely present in populations that survived oxygen stress but due to the primers utilized in this study can’t be explicitly linked to methanogens.