Some properties of methane oxidation in a thermally stratified lake

Abstract

Profiles of ¹⁴CH₄ and ¹⁴CO oxidation and concentrations of CH₄, NH₄⁺ , and nitrogen oxides (N₂O, NH₂^- , NH₃^- ) were studied in Lake St. George, Ontario, during late summer stratification. Metalimnetic maxima of the nitrogen oxides occurred and high rates of oxidation of CH₄ and CO were limited to a narrow band (4 and CO was strongly inhibited by the nitrification inhibitor allylthiourea. The affinity of the oxidizers for CH₄ (approximate K_m = 4.6 µM), their sensitivity to picolinic acid, and the ratio of CH₄ oxidation to allylthiourea-sensitive CO oxidation together suggest that methanotrophs were responsible for the observed CH₄ oxidation. Pure cultures of Nitrosomonas europaea, although less sensitive to picolinic acid than the CH₄ oxidizers of Lake St. George, were affected by the inhibitor (approximate K_i for inhibition of NH₄⁺ oxidation = 51 µM).