Raju P N, Evans H J, Seidler R J
Department of Botany, Oregon State University, Corvallis, Oreg. 97331.
Proc Natl Acad Sci U S A. 1972 Nov;69(11):3474-8. doi: 10.1073/pnas.69.11.3474.
Examination of root systems and adhering soil associated with unusually green corn plants from nitrogen-deficient areas in fields has revealed higher acetylene-reducing activities than comparable root systems of chlorotic plants that appeared to be nitrogen deficient. From the root systems with acetylene-reducing activity, N(2)-fixing Enterobacter cloacae were isolated. Pure cultures of the organism grown in a medium lacking added fixed nitrogen reduced acetylene to ethylene and used N(2) as a sole source of nitrogen under anaerobic conditions. Acetylene reduction was strikingly inhibited by 0.04 atm or greater partial pressures of O(2); however, the bacteria maintained appreciable acetylene-reducing rates in medium exposed to partial pressures of O(2) ranging from 0.005 to 0.015 atm. Nitrogenase activity in cell-free extracts of the bacterium was dependent upon Na(2)S(2)O(4) and an ATP-generating system. Some environmental conditions expected to influence N(2) fixation by free-living N(2)-fixing bacteria on root surfaces of nonlegumes are discussed.
对田间缺氮区域异常绿色玉米植株的根系及附着土壤进行检测发现，其乙炔还原活性高于看似缺氮的褪绿植株的可比根系。从具有乙炔还原活性的根系中分离出了固氮阴沟肠杆菌。该微生物在缺乏添加固定氮的培养基中生长的纯培养物，在厌氧条件下将乙炔还原为乙烯，并将N₂作为唯一氮源。0.04个大气压或更高的氧气分压会显著抑制乙炔还原；然而，在暴露于0.005至0.015个大气压氧气分压的培养基中，这些细菌仍保持可观的乙炔还原速率。该细菌无细胞提取物中的固氮酶活性依赖于连二亚硫酸钠和一个ATP生成系统。文中讨论了一些预期会影响非豆科植物根表面自由生活的固氮细菌固氮作用的环境条件。
