title: Thermodynamics of formate-oxidizing metabolism and implications for H2 production.
abstract: Formate-dependent proton reduction to H(2) (HCOO(-) + H(2)O → HCO(3)(-) + H(2)) has been reported for hyperthermophilic Thermococcus strains. In this study, a hyperthermophilic archaeon, Thermococcus onnurineus strain NA1, yielded H(2) accumulation to a partial pressure of 1 × 10(5) to 7 × 10(5) Pa until the values of Gibbs free energy change (ΔG) reached near thermodynamic equilibrium (-1 to -3 kJ mol(-1)). The bioenergetic requirement for the metabolism to conserve energy was demonstrated by ΔG values as small as -5 kJ mol(-1), which are less than the biological minimum energy quantum, -20 kJ mol(-1), as calculated by Schink (B. Schink, Microbiol. Mol. Biol. Rev. 61:262-280, 1997). Considering formate as a possible H(2) storage material, the H(2) production potential of the strain was assessed. The volumetric H(2) production rate increased linearly with increasing cell density, leading to 2,820 mmol liter(-1) h(-1) at an optical density at 600 nm (OD(600)) of 18.6, and resulted in the high specific H(2) production rates of 404 ± 6 mmol g(-1) h(-1). The H(2) productivity indicates the great potential of T. onnurineus strain NA1 for practical application in comparison with H(2)-producing microbes. Our result demonstrates that T. onnurineus strain NA1 has a highly efficient metabolic system to thrive on formate in hydrothermal systems.
authors.affiliation: Korea Institute of Ocean Science and Technology, Ansan, South Korea.
authors.forename: Jae Kyu
authors.initials: JK
authors.lastname: Lim
authors.forename: Seung Seob
authors.initials: SS
authors.lastname: Bae
authors.forename: Tae Wan
authors.initials: TW
authors.lastname: Kim
authors.forename: Jung-Hyun
authors.initials: JH
authors.lastname: Lee
authors.forename: Hyun Sook
authors.initials: HS
authors.lastname: Lee
authors.forename: Sung Gyun
authors.initials: SG
authors.lastname: Kang
mesh_terms: D005561:Formates / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D010084:Oxidation-Reduction; D019712:Thermococcus / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D005561:Formates; C030544:formic acid; D006859:Hydrogen