Hydrogen accumulation by H2-uptake negative strains of Rhizobium

SummaryHydrogen evolution from root nodules has been reported to decrease the efficiency of the nitrogen fixing system. Mutants ofRhizobium meliloti andRhizobium leguminosarum were selected which were deficient in H2-uptake capacity (Hup−). The relative efficiency of the nitrogen fixation for both species assessed with C2H2 reduction was 0.66.The hydrogen production was monitored using a simple root incubation method. As such, hydrogen production up to 3.83 and 15.57 ml.day−1.g−1 plant dry weight were recorded forPisum sativum — Rhizobium leguminosarum 4.20 Hup− andMedicago sativa — Rhizobium meliloti 1.5 Hup− respectively. In a closed container (250 ml), hydrogen concentrations up to 20% (v/v) could be reached in the root phase ofMedicago sativa in a time period of 320 hours.