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.

Engineering Pseudomonas protegens Pf-5 for nitrogen fixation and its application to improve plant growth under nitrogen-deficient conditions.

Abstract: Nitrogen is the second most critical factor for crop production after water. In this study, the beneficial rhizobacterium Pseudomonas protegens Pf-5 was genetically modified to fix nitrogen using the genes encoding the nitrogenase of Pseudomonas stutzeri A1501 via the X940 cosmid. Pf-5 X940 was able to grow in L medium without nitrogen, displayed high nitrogenase activity and released significant quantities of ammonium to the medium. Pf-5 X940 also showed constitutive expression and enzymatic activity of nitrogenase in ammonium medium or in nitrogen-free medium, suggesting a constitutive nitrogen fixation. Similar to Pseudomonas protegens Pf-5, Pseudomonas putida, Pseudomonas veronii and Pseudomonas taetrolens but not Pseudomonas balearica and Pseudomonas stutzeri transformed with cosmid X940 showed constitutive nitrogenase activity and high ammonium production, suggesting that this phenotype depends on the genome context and that this technology to obtain nitrogen-fixing bacteria is not restricted to Pf-5. Interestingly, inoculation of Arabidopsis, alfalfa, tall fescue and maize with Pf-5 X940 increased the ammonium concentration in soil and plant productivity under nitrogen-deficient conditions. In conclusion, these results open the way to the production of effective recombinant inoculants for nitrogen fixation on a wide range of crops.

Growth and carbon content of three different‐sized diazotrophic cyanobacteria observed in the subtropical north pacific1

Abstract: To develop tools for modeling diazotrophic growth in the open ocean, we determined the maximum growth rate and carbon content for three diazotrophic cyanobacteria commonly observed at Station ALOHA (A Long-term Oligotrophic Habitat Assessment) in the subtropical North Pacific: filamentous nonheterocyst-forming Trichodesmium and unicellular Groups A and B. Growth-irradiance responses of Trichodesmium erythraeum Ehrenb. strain IMS101 and Crocosphaera watsonii J. Waterbury strain WH8501 were measured in the laboratory. No significant differences were detected between their fitted parameters (±CI) for maximum growth rate (0.51 ± 0.09 vs. 0.49 ± 0.17 d(-1) ), half-light saturation (73 ± 29 vs. 66 ± 37 μmol quanta · m(-2) · s(-1) ), and photoinhibition (0 and 0.00043 ± 0.00087 [μmol quanta · m(-2) · s(-1) ](-1) ). Maximum growth rates and carbon contents of Trichodesmium and Crocosphaera cultures conformed to published allometric relationships, demonstrating that these relationships apply to oceanic diazotrophic microorganisms. This agreement promoted the use of allometric models to approximate unknown parameters of maximum growth rate (0.77 d(-1) ) and carbon content (480 fg C · μm(-3) ) for the uncultivated, unicellular Group A cyanobacteria. The size of Group A was characterized from samples from the North Pacific Ocean using fluorescence-activated cell sorting and real-time quantitative PCR techniques. Knowledge of growth and carbon content properties of these organisms facilitates the incorporation of different types of cyanobacteria in modeling efforts aimed at assessing the relative importance of filamentous and unicellular diazotrophs to carbon and nitrogen cycling in the open ocean.

A Nodule-Specific Plant Protein (Nodulin-35) from Soybean

Abstract: Nodulin-35, a 35,000-molecular-weight protein, is present in soybean root nodules developed by different strains of Rhizobium japonicum, irrespective of their effectiveness in fixing atmospheric nitrogen. This protein is not detected in uninfected plants and bacteroids or in free-living Rhizobium and appears to be synthesized by the plant during the formation of root nodules.

Establishment of nitrogen-fixing and phosphate-solubilising bacteria in rhizosphere and their effect on yield and nutrient uptake of wheat crop

Abstract: The factors that influence inocula establishmentviz. soil fertility, organic manuring and interactions between Azotobacter and phosphobacteria were examined in unsterilised and sterilised soil with and without farm yard manure in green house conditions. During the experiments, the number of nitrogen-fixing and phosphate-solubilising bacteria were enumerated. At the end of experiment, dry weight of grain and its nitrogen and phosphate uptake were determined. Increased number of both types of bacteria in rhizosphere soil and greater yield and nutrients uptake were observed, when seeds were bacterised with single or mixed cultures as compared to uninoculated treatment. The number of organisms remained quite high in mixed cultures and was so for longer periods of plant growth. Addition of 2% farmyard manure further enhanced the bacterial population and crop productivity. This effect was more pronounced in sterilised soil.