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Appl Environ Microbiol. 1978 August; 36(2): 330-340
Copyright © 1978 American Society for Microbiology. All Rights Reserved.

Kinetic Parameters of the Conversion of Methane Precursors to Methane in a Hypereutrophic Lake Sediment

Richard F. Strayer^,a and James M. Tiedje¹

^a Department of Microbiology and Public Health, Michigan State University, East Lansing, Michigan 48824
¹ Department of Crop and Soil Sciences, Michigan State University, East Lansing, Michigan 48824

ABSTRACT

The kinetic parameters K_m, V_max, T_t (turnover time), and v (natural velocity) were determined for H₂ and acetate conversion to methane by Wintergreen Lake sediment, using short-term (a few hours) methods and incubation temperatures of 10 to 14°C. Estimates of the Michaelis-Menten constant, K_m, for both the consumption of hydrogen and the conversion of hydrogen to methane by sediment microflora averaged about 0.024 µmol g^–1 of dry sediment. The maximal velocity, V_max, averaged 4.8 µmol of H₂ g^–1 h^–1 for hydrogen consumption and 0.64 µmol of CH₄ g^–1 h^–1 for the conversion of hydrogen to methane during the winter. Estimated natural rates of hydrogen consumption and hydrogen conversion to methane could be calculated from the Michaelis-Menten equation and estimates of K_m, V_max, and the in situ dissolved-hydrogen concentration. These results indicate that methane may not be the only fate of hydrogen in the sediment. Among several potential hydrogen donors tested, only formate stimulated the rate of sediment methanogenesis. Formate conversion to methane was so rapid that an accurate estimate of kinetic parameters was not possible. Kinetic experiments using [2-¹⁴C]acetate and sediments collected in the summer indicated that acetate was being converted to methane at or near the maximal rate. A minimum natural rate of acetate conversion to methane was estimated to be about 110 nmol of CH₄ g^–1 h^–1, which was 66% of the V_max (163 nmol of CH₄ g^–1 h^–1). A 15-min preincubation of sediment with 5.0 x 10^–3 atm of hydrogen had a pronounced effect on the kinetic parameters for the conversion of acetate to methane. The acetate pool size, expressed as the term K_m + S_n (S_n is in situ substrate concentration), decreased by 37% and T_t decreased by 43%. The V_max remained relatively constant. A preincubation with hydrogen also caused a 37% decrease in the amount of labeled carbon dioxide produced from the metabolism of [U-¹⁴C]valine by sediment heterotrophs.

Present address: Department of Agronomy, Cornell University, Ithaca, NY 14858.

Journal Article no. 8256 of the Michigan Agricultural Experiment Station; contribution no. 344 of the W. K. Kellogg Biological Station.