Enrichment for Hydrogen-Oxidizing Acinetobacter spp. in the Rhizosphere of Hydrogen-Evolving Soybean Root Nodules

Field soybean plants were inoculated with Hup⁺ wild-type or H₂ uptake-negative (Hup⁻) mutants of Bradyrhizobium japonicum. For two consecutive summers we found an enrichment for acinetobacters associated with the surfaces of the H₂-evolving nodules. Soybean root nodules that evolved H₂ had up to 12 times more Acinetobacter spp. bacteria associated with their surfaces than did nodules incapable of evolving H₂. All of the newly isolated strains identified as Acinetobacter obtained from the surfaces of root nodules, as well as known established Acinetobacter strains, were capable of oxidizing H₂, a property not previously described for this alkane-degrading soil bacterium.