CH₄, even at the meager atmospheric concentration of 1.9 ppmv, is responsible for ~20% of the total radiative forcing in a 100-year scale, and due to its short lifespan, active removal of the atmospheric CH₄ would have an immediacy benefit.1,2 However, the low concentration has proven to be a major impediment in development of viable atmospheric CH₄ removal technologies capable of attaining defacto CO₂-eq removal.

The best approach to this endeavor has always been suggested as employing the extraordinary capability of microorganisms to scavenge energy and carbon from even such sparse sources. Atmospheric CH₄ oxidizers have been scientifically pursued for decades, initially inspired by observations of negative CH₄ fluxes from various soil environments.3,4 Involvements of USCa and USCg clusters and the Methylocystis-specific particulate methane monooxygenase with higher affinity had been hypothesized.5,6 Recently, growth on <2 ppmv CH₄ was confirmed in several Methylocapsa isolates; however, their low CH₄ oxidation rates and extremely slow growths still leave unanswered questions as to their ecological significance or applicability as biocatalysts.

The problem to be addressed is how to elicit and sustain microbial atmospheric CH₄ oxidation activity of complex microbial consortia with occasional spiking with <100 ppmv CH₄. We will seek a mechanistic explanation for the observed atmospheric CH₄ consumption following excitation and means to extend the period to enable a net CH₄ removal.

The key goals include 1) confirmation an optimization of the observed atmospheric CH₄ oxidation following <100 ppmv spiking, 2) investigation of the ecophysiological mechanism underpinning the observed atmospheric CH₄ oxidation, 3) search of amendments to elongate and accelerate the periods of atmospheric CH₄ oxidation, and 3) design and feasibility test of a bioreactor where CH₄ generated from organic wastes fuels atmospheric CH₄ oxidation. Evaluation of success can be based on the establishment of an artificial microbiome (and eventually a miniature version of the proposed reactor) where net negative CH₄ flux can be achieved over a prolonged period (>2 months) and a well-explained-and-supported theoretical rationale for the microbiome behavior with regard to atmospheric CH₄ uptake.

If successful, this proposed study would make following contributions to the much-needed efforts to mitigate atmospheric CH₄.

• Improved understanding of negative fluxes of CH₄ repeatedly observed at CH₄ hotspots.
• Deciphering of the ecophysiology of atmospheric-CH₄-consuming microbiomes, including identification of the main methanotrophic players, interactions within the methanotrophic and non-methanotrophic constituents, and the conditions that accelerate and/or prolong CH₄ consumption by the consortia.
• Improved experimental and computational methodologies for studying the ecophysiology of CH₄-sink microbiomes, including improved metagenomic and metatranscriptomic pipelines for evasive genes encoding methane monooxygenases.
• Biotechnological advances that enable development of an economic and easy-to-build-and-operate engineered system capable of achieving a net removal of CH₄.