Identification of the Hydrogen Uptake Gene Cluster for Chemolithoautotrophic Growth and Symbiosis Hydrogen Uptake in Bradyrhizobium Diazoefficiens

摘要

The hydrogen uptake (Hup) system of Bradyrhizobium diazoefficiens recycles the H₂ released by nitrogenase in soybean nodule symbiosis, and is responsible for H₂-dependent chemolithoautotrophic growth. The strain USDA110 has two hup gene clusters located outside (locus I) and inside (locus II) a symbiosis island. Bacterial growth under H₂-dependent chemolithoautotrophic conditions was markedly weaker and H₂ production by soybean nodules was markedly stronger for the mutant of hup locus I ( ΔhupS ₁ L ₁ ) than for the mutant of hup locus II ( ΔhupS ₂ L ₂ ). These results indicate that locus I is primarily responsible for Hup activity.