Symbiotic Bradyrhizobium japonicum Reduces N sub(2)O Surrounding the Soybean Root System via Nitrous Oxide Reductase

• Published in: Applied and environmental microbiology 2006-04, Vol.72 (4), p.2526-2532
• Main Authors: Sameshima-Saito, Reiko, Chiba, Kaori, Hirayama, Junta, Itakura, Manabu, Mitsui, Hisayuki, Eda, Shima, Minamisawa, Kiwamu
• Format: Article
• Language: English
• Subjects: Bradyrhizobium japonicum
• ISSN: 0099-2240; 1098-5336

N sub(2)O reductase activity in soybean nodules formed with Bradyrhizobium japonicum was evaluated from N sub(2)O uptake and conversion of super(15)N-N sub(2)O into super(15)N-N sub(2). Free-living cells of USDA110 showed N sub(2)O reductase activity, whereas a nosZ mutant did not. Complementation of the nosZ mutant with two cosmids containing the nosRZDFYLX genes of B. japonicum USDA110 restored the N sub(2)O reductase activity. When detached soybean nodules formed with USDA110 were fed with super(15)N-N sub(2)O, they rapidly emitted super(15)N-N sub(2) outside the nodules at a ratio of 98.5% of super(15)N-N sub(2)O uptake, but nodules inoculated with the nosZ mutant did not. Surprisingly, N sub(2)O uptake by soybean roots nodulated with USDA110 was observed even in ambient air containing a low concentration of N sub(2)O (0.34 ppm). These results indicate that the conversion of N sub(2)O to N sub(2) depends exclusively on the respiratory N sub(2)O reductase and that soybean roots nodulated with B. japonicum carrying the nos genes are able to remove very low concentrations of N sub(2)O.