Difference in survival of uptake hydrogenase positive and negative strains ofBradyrhizobium japonicumin flooded and non-flooded soil

Hydrogen gas evolves through the nitrogenase activity while dinitrogen is reduced to ammonia. A part of hydrogen gas is oxidized by the uptake hydrogenase of diazotrophs for the recovery of some portions of ATP consumed by the nitrogenase. The extent of H2 recycling varies with the species and strains of rhizobia (review by Evans et al. 1987). Beneficial effect of H2 recycling on nodule nitrogen fixation has been studied extensively and contradictory results have been obtained (Evans et al. 1987). Uptake hydrogenase positive, Hup(+), strains of Bradyrhizobium japonicum are capable of chemolithotrophic growth using H2, CO2, and O2 in culture media (Hanus et al. 1979) and sterile soil (Lambert et al. 1985).