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 muM. 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 degrees 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 degrees 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 degrees 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.