Metabolism of Formate in Methanobacterium formicicum

Abstract

Methanobacterium formicicum strain JF-1 was cultured with formate as the sole energy source in a pH-stat fermentor. Growth was exponential, and both methane production and formate consumption were linear functions of the growth rate. Hydrogen was produced in only trace amounts, and the dissolved H 2 concentration of the culture medium was below 1 μM. The effect of temperature or pH on the rate of methane formation was studied with a single fermentor culture in mid-log phase that was grown with formate under standard conditions at 37°C and pH 7.6. Methane formation from formate occurred over the pH range from 6.5 to 8.6, with a maximum at pH 8.0. The maximum temperature of methanogenesis was 56°C. H 2 production increased at higher temperatures. Hydrogen and formate were consumed throughout growth when both were present in saturating concentrations. The molar growth yields were 1.2 ± 0.06 g (dry weight) per mol of formate and 4.8 ± 0.24 g (dry weight) per mol of methane. Characteristics were compared for cultures grown with either formate or H 2 -CO 2 as the sole energy source at 37°C and pH 7.6; the molar growth yield for methane of formate cultures was 4.8 g (dry weight) per mol, and that of H 2 -CO 2 cultures was 3.5 g (dry weight) per mol. Both formate and H 2 -CO 2 cultures had low efficiencies of electron transport phosphorylation; formate-cultured cells had greater specific activities of coenzyme F 420 than did H 2 -CO 2 -grown cultures. Hydrogenase, formate dehydrogenase, chromophoric factor F 342 , and low levels of formyltetrahydrofolate synthetase were present in cells cultured with either substrate. Methyl viologen-dependent formate dehydrogenase was found in the soluble fraction from broken cells.