Oxyleghemoglobin-mediated Hydrogen Oxidation by Rhizobium japonicum USDA 122 DES Bacteroids

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Abstract
Oxyleghemoglobin was used to supply low concentrations of O2 to H2-oxidizing bacteroids from R. japonicum USDA 122 DES. The H2 oxidation system of these bacteroids was capable of effectively utilizing O2 at the low concentrations of O2 expected to be found in the soybean nodules. Apparent Km values of approximately 10 nm O2 were calculated for the oxyhydrogen reaction. These values include the Km values for both H2 oxidation and endogenous substrate oxidation. Even in the presence of oxyleghemoglobin, H2 additions stimulated C2H2 reduction, reduced the rate of endogenous respiration and maintained the ATP contents of bacteroids. In this reconstituted oxyleghemoglobin and bacteroid system, the H2 oxidation system is capable of recycling all of the H2 evolved during the N2 fixation process.