Effect of limited nickel availability on methane emission from EDTA treated soils: coenzyme M an alternative biomarker for methanogens.

Methanogens utilize simple carbon compounds to produce methane (CH(4)) under strictly anaerobic condition. During methanogenesis, methyl coenzyme M (MeCoM) is reduced by MeCoM reductase enzyme to CH(4) involving a nickel-containing cofactor F(430). In this experiment, strong chelating agent like ethylenediaminetetraacetic acid (EDTA) was applied in soil to study its feasibility for suppressing methanogen activity and CH(4) production in soil. Application of EDTA significantly (P≤0.05) reduced CH(4) production in soil. Application of 60 ppm EDTA (soil weight basis) was the most effective among all treatments. Applied EDTA forms complex compounds with heavy metals like nickel (Ni) and increases Ni concentration in soil solution. Since methanogenesis is intracellular process, it is necessary for methanogens to assimilate those Ni-EDTA complexes inside cell to utilize Ni in EDTA treated soils. Results indicated that methanogens cannot utilize Ni in the presence of EDTA and that significantly (P≤0.05) reduced mcrA gene (coding MeCoM reductase enzyme) copy number and Co-M concentration in soil. Due to high correlation (r=0.901(*)) between Co-M concentration and mcrA gene copy numbers, Co-M concentration could be used as an alternative biomarker for methanogens. Therefore, it could be propose that 60 ppm EDTA could be an optimum dose to suppress CH(4) emission from soil by restricting Ni availability to methanogens.