Competition for electrons favours N O reduction in denitrifying Bradyrhizobium isolates.

Bradyrhizobia are common members of soil microbiomes and known as N -fixing symbionts of economically important legumes. Many are also denitrifiers, which can act as sinks or sources for N O. Inoculation with compatible rhizobia is often needed for optimal N -fixation, but the choice of inoculant may have consequences for N O emission.

Host Range and Symbiotic Effectiveness of NO Reducing Strains.

Emissions of the potent greenhouse gas NO is one of the environmental problems associated with intensive use of synthetic N fertilizers, and novel NO mitigation strategies are needed to minimize fertilizer applications and NO release without affecting agricultural efficiencies. Increased incorporation of legume crops in agricultural practices offers a sustainable alternative. Legumes, in their symbiosis with nitrogen fixing bacteria, rhizobia, reduce the need for fertilizers and also respond to the need for increased production of plant-based proteins.

A common mechanism for efficient N O reduction in diverse isolates of nodule-forming bradyrhizobia.

Bradyrhizobia are abundant soil bacteria, which can form nitrogen-fixing symbioses with leguminous plants, including important crops such as soybean, cowpea and peanut. Many bradyrhizobia can denitrify, but studies have hitherto focused on a few model organisms. We screened 39 diverse Bradyrhizobium strains, isolated from legume nodules.

Phylogenetically diverse groups of Bradyrhizobium isolated from nodules of tree and annual legume species growing in Ethiopia.

Bacteria belonging to the genus Bradyrhizobium nodulate various leguminous woody plants and herbs, including economically important crops such as soybean, peanut and cowpea. Here we analysed 39 Bradyrhizobium strains originating from root nodules of the leguminous trees and crops Acacia saligna, Faidherbia albida, Erythrina brucei, Albizia gummifera, Millettia ferruginea, Cajanus cajan, Vigna unguiculata and Phaseolus vulgaris, growing in southern Ethiopia. Multilocus sequence analyses (MLSA) of the 16S rRNA, glnII, recA, gyrB and dnaK genes and the ITS region grouped the test strains into seven well-supported genospecies (I-VII), six of which occupied distinct positions excluding all hitherto defined Bradyrhizobium species.