Response of mixed methanotrophic consortia to different methane to oxygen ratios

Methane (CH₄) and oxygen (air) concentrations affect the CH₄ oxidation capacity (MOC) and mixed methanotrophic community structures in compost (fresh) and landfill (age old) top cover soils. A change in the mixed methanotrophic community structure in response has implications for landfill CH₄ bio-filter remediation and possible bio-product outcomes (i.e., fatty acid methyl esters (FAME) content and profiles and polyhydroxybutyrate (PHB) contents). Therefore the study aimed to evaluate the effect of variable CH₄ to oxygen ratios (10–50% CH₄ in air) on mixed methanotrophic community structures enriched from landfill top cover (LB) and compost soils (CB) and to quantify flow on impacts on MOC, total FAME contents and profiles, and PHB accumulation. A stable consortium developed achieving average MOCs of 3.0 ± 0.12, 4.1 ± 0.26, 6.9 ± 0.7, 7.6 ± 1.3 and 9.2 ± 1.2 mg CH₄ g⁻¹ DW_biomass h⁻¹ in LB and 2.9 ± 0.04, 5.05 ± 0.32, 6.7 ± 0.31, 7.9 ± 0.61 and 8.6 ± 0.48 mg CH₄ g⁻¹ DW_biomass h⁻¹ in CB for a 20 day cultivation period at 10, 20, 30, 40 and 50% CH₄, respectively. CB at 10% CH₄ had a maximal FAME content of 40.5 ± 0.8 mg FAME g⁻¹ DW_biomass, while maximal PHB contents (25 mg g⁻¹ DW_biomass) was observed at 40% CH₄ in LB. Despite variable CH₄/O₂ ratios, the mixed methanotrophic community structures in both LB and CB were relatively stable, dominated by Methylosarcina sp., and Chryseobacterium, suggesting that a resilient consortium had formed which can now be tested in bio-filter operations for CH₄ mitigations in landfills.