Rhizobium etli is able to emit nitrous oxide by connecting assimilatory nitrate reduction with nitrite respiration in the bacteroids of common bean nodules

Legumes can contribute to emissions of the potent greenhouse gas nitrous oxide (N 2 O) directly by some rhizobia species that are able to denitrify under free-living conditions and in symbiotic association with the plant. In this study, the capacity of Phaseolus vulgaris - Rhizobium etli symbiosis to emit N 2 O in response to nitrate (NO 3) has been demonstrated for the fi rst time. We found that bacteroidal assimilatory nitrate reductase (NarB) as well as nitrite reductase (NirK) and nitric oxide reductase (cNor) denitrifying enzymes contribute to nitric oxide (NO) and N 2 O formation in nodules. We also show that R. etli NarK is involved in NO 2-extrusion and links NO 3-reduction by NarB in the cytoplasm with NirK and cNor denitri fi cation activities in the periplasm. The knowledge generated in this work will be instrumental for exploring strategies and sustainable practices in agricultural soil management to increase legume crop yield and mitigate greenhouse gas emissions