Kinetics of Formate Metabolism in Methanobacterium formicicum and Methanospirillum hungatei

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Abstract
The kinetics of formate metabolism in Methanobacterium formicicum and Methanospirillum hungatei were studied with log-phase formate-grown cultures. The progress of formate degradation was followed by the formyltetrahydrofolate synthetase assay for formate and fitted to the integrated form of the Michaelis-Menten equation. The K m and V max values for Methanobacterium formicicum were 0.58 mM formate and 0.037 mol of formate h −1 g −1 (dry weight), respectively. The lowest concentration of formate metabolized by Methanobacterium formicicum was 26 μM. The K m and V max values for Methanospirillum hungatei were 0.22 mM and 0.044 mol of formate h −1 g −1 (dry weight), respectively. The lowest concentration of formate metabolized by Methanospirillum hungatei was 15 μM. The apparent K m for formate by formate dehydrogenase in cell-free extracts of Methanospirillum hungatei was 0.11 mM. The K m for H 2 uptake by cultures of Methanobacterium formicicum was 6 μM dissolved H 2 . Formate and H 2 were equivalent electron donors for methanogenesis when both substrates were above saturation; however, H 2 uptake was severely depressed when formate was above saturation and the dissolved H 2 was below 6 μM. Formate-grown cultures of Methanobacterium formicicum that were substrate limited for 57 h showed an immediate increase in growth and methanogenesis when formate was added to above saturation.