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영어

A new hydrogen-oxidizing bacterium, Aeromonas sp. strain JS-1, that can fix CO2 via the reductive pentose phosphate cycle (Calvin-Benson cycle) under chemoautotrophic conditions but not photoautotrophic conditions was isolated from fresh water. Strain JS-1 showed considerable CO2 fixation ability during continuous cultivation even at high CO2 concentration. Strain JS-1 used H2 and CO2 fixation as energy and carbon sources, respectively. Carbon dioxide fixation is carried out through the Calvin-Benson cycle, in which ribulose-1,5-bisphosphate carboxylase/ oxygenase (RubisCO) is the key enzyme. Hydrogen-oxidizing chemoautotrophic Aeromonas sp. strain JS-1 exhibited remarkedly strong RubisCO [EC 4.1.1.39] activity. RubisCO was purified as an L8S8-type hexadecamer with molecular mass of 560 kDa by gel filtration. The enzyme consisted of two different subunits eight large (56 kDa) and eight small (15 kDa), as demonstrated by SDS-PAGE. The specific activity of the purified enzyme was about 3.31 unit/mg and stable up to 45℃. The Km values for RuBP, CO2, and Mg2+ were estimated to be 0.25 mM, 5.2 mM and 0.91 mM, respectively.