Nitrogen fixation

About: Nitrogen fixation is a research topic. Over the lifetime, 7940 publications have been published within this topic receiving 232921 citations. The topic is also known as: GO:0009399.

N2 fixation in phototrophs: adaptation to a specialized way of life

Abstract: Phototrophic diazotrophs include the photosynthetic green and purple bacteria, the heliobacteria, many cyanobacteria and the unusual chlorophyll-containing rhizobia that are found in the stem nodules of Aeschynomene spp. In this review, which concentrates on cyanobacteria, the interrelations between photosynthesis and N2 fixation are discussed. Photosynthesis can, in theory, directly provide the ATP and reductant needed to support N2 fixation but the link between these two processes is usually indirect, mediated through accumulated carbon reserves. In cyanobacteria, which possess an oxygenic photosynthesis, this serves to separate the O2 that is produced by photosynthesis from the O2-sensitive nitrogenase. However, in certain circumstances, oxygenic photosynthesis and N2 fixation coexist. Under these conditions, respiratory consumption of photosynthetically generated O2 may have an important role in minimizing O2-damage to nitrogenase.

Respiration and Nitrogen Fixation in Azotobacter

Abstract: Publisher Summary The chapter focuses on the work done toward this aspect; toward understanding how respiration and nitrogen fixation can function simultaneously in Azotobacter. Accordingly, only those aspects of this subject that are connected with the physiology of nitrogen fixation in aerobes will be discussed. In particular, determination of the constitution and behavior of this organism's branched respiratory chain has contributed to the understanding of how respiration controls nitrogen fixation. All nitrogenases from both aerobic and anaerobic organisms comprise two non-haem iron proteins, which have the same requirements for enzymic activity in vitro— namely, an anaerobic environment, a source of ATP, and a reluctant. The two component proteins that make up the nitrogenase enzyme complement each other in cross reactions between nitrogenase fractions from aerobic and some anaerobic sources and physiological electron carriers from one class of bacteria can donate electrons to nitrogenase from the other. The absence of oxygen is mandatory in nearly all measurements of nitrogen fixation in vitro. Crude preparations that show nitrogenase activity in the presence of oxygen have been obtained from aerobic nitrogen fixers. From the foregoing evidence it is reasonable to assume that nitrogen fixation is an anaerobic process catalyzed by oxygen-sensitive proteins. How these operate and survive in an aerobic bacterium is discussed in detail. Because oxygen uptake is the major electron-utilizing metabolic process in Azotobacter, the respiratory chain involving electron transport and oxidative phosphorylation are described.

Azospirillum effects on susceptibility to Rhizobium nodulation and on nitrogen fixation of several forage legumes

Abstract: Azospirillum brasilense Cd cell concentration of 105–107 colony-forming units (cfu)/mL applied 24 h before Rhizobium (106 cfu/mL), increased nodule formation in the non root hair zone, more than tw...

Development of catalytic nitrogen fixation using transition metal–dinitrogen complexes under mild reaction conditions

Abstract: This paper describes our recent progress in catalytic nitrogen fixation using transition metal–dinitrogen complexes as catalysts. Our research group has recently developed novel reaction systems for the catalytic transformation of molecular dinitrogen into ammonia and hydrazine using molybdenum–, iron–, cobalt– and vanadium–dinitrogen complexes under mild reaction conditions. The new findings presented in this paper may provide a new approach to the development of economical nitrogen fixation to replace the energy-consuming Haber–Bosch process.

Effects of Nitrate and Ammonium on Nitrogenase (C2H2 Reduction) Activity of Swards of Subterranean Clover, Trifolium subterraneum L.

Abstract: Small swards of subterranean clover plants were grown under controlled conditions without mineral nitrogen and allowed to establish an effective nitrogen fixation system. Nutrient solutions containing nitrate from 0 to 16 mM or of ammonium from 0 to 5 mM were then applied and changes in nitrogenase activity (NA) estimated by acetylene reduction assay (AR) and the rate of hydrogen evolution (HE) for periods of up to 35 days. In two experiments a split-root system was used to enable mineral nitrogen to be applied to only one-half of a nodulated root system whilst the NA of both halves was monitored. NA by subterranean clover was very sensitive to exogenous mineral nitrogen, concentrations as low as 0.5 mM NO3- suppressing activity significantly, and 3-5 mM stopping it almost completely within 7 days. The degree of inhibition induced by concentrations between 0.5 and 3 mM NO3- was less at a photon irradiance of 1000 compared with 300 µmol quanta s-1 m-2 . Under some conditions NA continued at a reduced but steady rate in the presence of nitrate. NH4+ also markedly depressed NA but a concentration greater than 5 mM was needed to effect the same response. After NO3- was applied to an active symbiosis, nitrate reductase activity increased as NA decreased. Our results do not support the hypothesis of a direct effect of NO3- on nitrogenase due to the accumulation of toxic NO2-. Although our results allow that assimilate might be diverted from the nodules after the application of NO3- thus reducing N2-fixation, an alternative hypothesis is proposed: that nitrogenase and nitrate reductase work in a complementary manner in supplying reduced nitrogen to whole plants, and NO3- depresses N2-fixation through a regulatory system involving the level of soluble nitrogen in the plant. We conclude that nitrogen fixation by subterranean clover in the field may be depressed below its potential due to the presence of soil mineral nitrogen.