Growth parameters (K _s, μ_max, Y _s) of Methanobacterium thermoautotrophicum

Abstract

Methanobacterium thermoautotrophicum was grown on a mineral salts medium in a fermenter gassed with H₂ and CO₂, which were the sole carbon and energy sources. Under the conditions used the bacterium grew exponentially. The dependence of the growth rate (μ) on the concentration of H₂ and CO₂ in the incoming gas and the dependence of the growth yield ($Y_{CH_4 }$) on the growth rate were determined at pH 7 (the pH optimum) and 65° C (the temperature optimum).

The curves relating growth rate to the H₂ and CO₂ concentration were hyperbolic. From reciprocal plots apparent K _s values for H₂ and CO₂ and μ_max were obtained: app. $K_{{\text{H}}_{\text{2}} }$ = 20%; app. $K_{{\text{CO}}_{\text{2}} }$ = 11%; μ = 0.69 h^-1; t _δ (max)=1 h.

$Y_{CH_4 }$ was 1.6 g mol^-1 and almost independent of the growth rate, when the rate of methane formation was not limited by the supply of either H₂ or CO₂. The yield increased to near 3 g mol^-1 when H₂ or CO₂ were limiting. These findings indicate that methane formation and growth are less tightly coupled at high concentrations of H₂ or CO₂ in the medium than at low concentrations. The physiological significance of these findings is discussed.