scholarly journals Manipulating nitrogen regulation in diazotrophic bacteria for agronomic benefit

2019 ◽  
Vol 47 (2) ◽  
pp. 603-614 ◽  
Author(s):  
Marcelo Bueno Batista ◽  
Ray Dixon
Keyword(s):  
Nitrogen Fixation ◽  
Genetic Manipulation ◽  
Current Knowledge ◽  
Ammonia Excretion ◽  
Ammonium Assimilation ◽  
Regulatory Mechanisms ◽  
Diazotrophic Bacteria ◽  
Fixed Nitrogen ◽  
Regulatory Circuits ◽  
Biological Nitrogen

AbstractBiological nitrogen fixation (BNF) is controlled by intricate regulatory mechanisms to ensure that fixed nitrogen is readily assimilated into biomass and not released to the environment. Understanding the complex regulatory circuits that couple nitrogen fixation to ammonium assimilation is a prerequisite for engineering diazotrophic strains that can potentially supply fixed nitrogen to non-legume crops. In this review, we explore how the current knowledge of nitrogen metabolism and BNF regulation may allow strategies for genetic manipulation of diazotrophs for ammonia excretion and provide a contribution towards solving the nitrogen crisis.

scholarly journals Genetic determinants of ammonia excretion in nifL mutants of Azotobacter vinelandii

2021 ◽  
Author(s):  
Florence Mus ◽  
Devanshi Khokhani ◽  
Esther Rugoli ◽  
Ray Dixon ◽  
Jean-Michel Ané ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Azotobacter Vinelandii ◽  
Model Organism ◽  
Ammonia Excretion ◽  
Promoter Sequence ◽  
Genetic Determinants ◽  
Two Component System ◽  
Opposite Orientation ◽  
Fixed Nitrogen ◽  
Biological Nitrogen

Abstract The ubiquitous diazotrophic soil bacterium Azotobacter vinelandii has been extensively studied as a model organism for biological nitrogen fixation (BNF). In A. vinelandii, BNF is regulated by the NifL-NifA two-component system, where NifL acts as an anti-activator that tightly controls that activity of the nitrogen fixation specific transcriptional activator, NifA, in response to redox, nitrogen, and carbon status. While several studies reported mutations in A. vinelandii nifL resulted in the deregulation of nitrogenase expression and the release of large quantities of ammonia, knowledge about the specific determinants for this ammonia-excreting phenotype is lacking. In this work, we report that only specific disruptions of nifL lead to large quantities of ammonia accumulated in liquid culture (~ 12 mM). The ammonia excretion phenotype is solely associated with deletions of NifL domains combined with the insertion of a promoter sequence in the opposite orientation to nifLA transcription. We further demonstrated that the strength of the inserted promoter could influence the amounts of ammonia excreted by affecting rnf1 gene expression as an additional requirement for ammonia excretion. These ammonia-excreting nifL mutants significantly stimulate the transfer of fixed nitrogen to rice. This work defines the discreet determinants that bring about A. vinelandii ammonia excretion and demonstrates that strains can be generated through simple gene editing to provide promising biofertilizers capable of transferring nitrogen to crops.

scholarly journals Competition, Nodule Occupancy, and Persistence of Inoculant Strains: Key Factors in the Rhizobium-Legume Symbioses

2021 ◽  
Vol 12 ◽  
Author(s):  
Marcela Mendoza-Suárez ◽  
Stig U. Andersen ◽  
Philip S. Poole ◽  
Carmen Sánchez-Cañizares
Keyword(s):  
Nitrogen Fixation ◽  
Current Knowledge ◽  
Local Environment ◽  
Nitrogen Fertilizers ◽  
Superior Performance ◽  
Nodule Occupancy ◽  
Inoculant Strain ◽  
Native Strains ◽  
Biological Nitrogen ◽  
Rhizobial Inoculants

Biological nitrogen fixation by Rhizobium-legume symbioses represents an environmentally friendly and inexpensive alternative to the use of chemical nitrogen fertilizers in legume crops. Rhizobial inoculants, applied frequently as biofertilizers, play an important role in sustainable agriculture. However, inoculants often fail to compete for nodule occupancy against native rhizobia with inferior nitrogen-fixing abilities, resulting in low yields. Strains with excellent performance under controlled conditions are typically selected as inoculants, but the rates of nodule occupancy compared to native strains are rarely investigated. Lack of persistence in the field after agricultural cycles, usually due to the transfer of symbiotic genes from the inoculant strain to naturalized populations, also limits the suitability of commercial inoculants. When rhizobial inoculants are based on native strains with a high nitrogen fixation ability, they often have superior performance in the field due to their genetic adaptations to the local environment. Therefore, knowledge from laboratory studies assessing competition and understanding how diverse strains of rhizobia behave, together with assays done under field conditions, may allow us to exploit the effectiveness of native populations selected as elite strains and to breed specific host cultivar-rhizobial strain combinations. Here, we review current knowledge at the molecular level on competition for nodulation and the advances in molecular tools for assessing competitiveness. We then describe ongoing approaches for inoculant development based on native strains and emphasize future perspectives and applications using a multidisciplinary approach to ensure optimal performance of both symbiotic partners.

scholarly journals Role of Diazotrophic Bacteria in Biological Nitrogen Fixation and Plant Growth Improvement

2016 ◽  
Vol 49 (1) ◽  
pp. 17-29 ◽  
Author(s):  
Wansik Shin ◽  
Rashedul Islam ◽  
Abitha Benson ◽  
Manoharan Melvin Joe ◽  
Kiyoon Kim ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Plant Growth ◽  
Biological Nitrogen Fixation ◽  
Diazotrophic Bacteria ◽  
Biological Nitrogen

Symbiosomes: temporary moonlighting organelles

2014 ◽  
Vol 460 (1) ◽  
pp. 1-11 ◽  
Author(s):  
David W. Emerich ◽  
Hari B. Krishnan
Keyword(s):  
Nitrogen Fixation ◽  
Symbiotic Nitrogen Fixation ◽  
Infected Plant ◽  
Plant Cells ◽  
Fixed Nitrogen ◽  
Moonlighting Proteins ◽  
Biological Nitrogen ◽  
Structural Entity ◽  
Leguminous Host

Symbiosomes are a unique structural entity that performs the role of biological nitrogen fixation, an energy-demanding process that is the primary entryway of fixed nitrogen into the biosphere. Symbiosomes result from the infection of specific rhizobial strains into the roots of an appropriate leguminous host plant forming an organ referred to as a nodule. Within the infected plant cells of the nodule, the rhizobia are encased within membrane-bounded structures that develop into symbiosomes. Mature symbiosomes create an environment that allows the rhizobia to differentiate into a nitrogen-fixing form called bacteroids. The bacteroids are surrounded by the symbiosome space, which is populated by proteins from both eukaryotic and prokaryotic symbionts, suggesting this space is the quintessential component of symbiosis: an inter-kingdom environment with the single purpose of symbiotic nitrogen fixation. Proteins associated with the symbiosome membrane are largely plant-derived proteins and are non-metabolic in nature. The proteins of the symbiosome space are mostly derived from the bacteroid with annotated functions of carbon metabolism, whereas relatively few are involved in nitrogen metabolism. An appreciable portion of both the eukaryotic and prokaryotic proteins in the symbiosome are also ‘moonlighting’ proteins, which are defined as proteins that perform roles unrelated to their annotated activities when found in an unexpected physiological environment. The essential functions of symbiotic nitrogen fixation of the symbiosome are performed by co-operative interactions of proteins from both symbionts some of which may be performing unexpected roles.

Nitrogen fixation in the high arctic tundra at Sarcpa Lake, Northwest Territories

1985 ◽  
Vol 63 (5) ◽  
pp. 974-979 ◽  
Author(s):  
Jim D. Karagatzides ◽  
Martin C. Lewis ◽  
Herbert M. Schulman
Keyword(s):  
Nitrogen Fixation ◽  
Northwest Territories ◽  
Acetylene Reduction ◽  
Biological Nitrogen Fixation ◽  
Arctic Tundra ◽  
High Arctic ◽  
Fixed Nitrogen ◽  
Free Living ◽  
Blue Green Algae ◽  
Biological Nitrogen

The acetylene reduction assay was used to examine biological nitrogen fixation in the high arctic tundra at Sarcpa Lake, Northwest Territories (68°32′ N, 83°19′ W). The highest rates of acetylene reduction (9.37 ± 3.19 μmol C2H4 m−2 h−1) were in habitats that had a high density of the legumes Oxytropis maydelliana, O. arctobia, and Astragalus alpinus. Nitrogen fixation in the wet soils along the shore of a small lake was similar (8.87 ± 4.35 μmol C2H4 m−2 h−1) because of the blue-green alga Nostoc, which associates with mosses. Free-living blue-green algae and lichens made insignificant contributions to the total nitrogen fixation budget because they were uncommon and fixed nitrogen at a slower rate. Nitrogen-fixing lichens in the area included Stereocaulon arenarium and S. rivulorum. It is concluded that legumes have a significant input to the biological nitrogen fixation budget at Sarcpa Lake.

scholarly journals Phosphate solubilizing bacteria stimulate wheat rhizosphere and endosphere biological nitrogen fixation by improving phosphorus content

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e9062
Author(s):  
Yongbin Li ◽  
Qin Li ◽  
Guohua Guan ◽  
Sanfeng Chen
Keyword(s):  
Nitrogen Fixation ◽  
Nitrogenase Activity ◽  
Available P ◽  
Plant Tissues ◽  
Diazotrophic Bacteria ◽  
Total N ◽  
P Content ◽  
Soil Available P ◽  
Biological Nitrogen ◽  
Total P

Phosphate (P) availability often limits biological nitrogen fixation (BNF) by diazotrophic bacteria. In soil, only 0.1% of the total P is available for plant uptake. P solubilizing bacteria can convert insoluble P to plant-available soluble P (ionic P and low molecular-weight organic P). However, limited information is available about the effects of synergistic application of diazotrophic bacteria and P solubilizing bacteria on the nitrogenase activity of rhizosphere and nifH expression of endosphere. In this study, we investigated the effects of co-inoculation with a diazotrophic bacterium (Paenibacillus beijingensis BJ-18) and a P-solubilizing bacterium (Paenibacillus sp. B1) on wheat growth, plant and soil total N, plant total P, soil available P, soil nitrogenase activity and the relative expression of nifH in plant tissues. Co-inoculation significantly increased plant biomass (length, fresh and dry weight) and plant N content (root: 27%, shoot: 30%) and P content (root: 63%, shoot: 30%). Co-inoculation also significantly increased soil total N (12%), available P (9%) and nitrogenase activity (69%) compared to P. beijingensis BJ-18 inoculation alone. Quantitative real-time PCR analysis showed co-inoculation doubled expression of nifH genes in shoots and roots. Soil nitrogenase activity and nifH expression within plant tissues correlated with P content of soil and plant tissues, which suggests solubilization of P by Paenibacillus sp. B1 increased N fixation in soils and the endosphere. In conclusion, P solubilizing bacteria generally improved soil available P and plant P uptake, and considerably stimulated BNF in the rhizosphere and endosphere of wheat seedlings.

scholarly journals Nodulation and Nitrogen Fixation of Pongamia pinnata

2017 ◽  
Vol 4 (1) ◽  
pp. 1-12
Author(s):  
Phoebe N. Calica
Keyword(s):  
Nitrogen Fixation ◽  
Symbiotic Nitrogen Fixation ◽  
Current Knowledge ◽  
Fixed Nitrogen ◽  
Qualitative And Quantitative ◽  
Naturally Occurring ◽  
Reduction Assay ◽  
Quantitative Results ◽  
Preliminary Study ◽  
Growth And Reproduction

Nitrogen is one of the most important nutrients required by plants as a major component of all nucleic acids and proteins such as enzymes which control and enable their growth and reproduction. While much research has been conducted on the legume tree Pongamia (a candidate source for renewable biofuel), there is only a handful of studies on the mechanisms and regulation of nitrogen fixation, which is considered as one of the most important domestication traits that needs to be investigated.  Steps to optimize the symbiotic nitrogen fixation of Pongamia is, firstly, to select the best rhizobial isolates as inoculum among the naturally-occurring pool of bacteria in soils across Queensland. There have been reports on rhizobia nodulating Pongamia isolated from Western Australia and India but not in Queensland, Australia. This study is the first to report such rhizobia isolates that nodulated Pongamia.  Secondly, is to establish efficient nodulation by studying the factors such as nitrate and salinity. The published literature has provided extensive details on the effects of these factors in nodulation and their mechanisms in various legumes. However, only one preliminary study was published from our laboratory; the present study is the in-depth continuation of that effort. Lastly, nitrogen fixation in Pongamia must be assessed to determine if fixed nitrogen is sufficient to support its growth and reproduction. Acetylene reduction assay is the simplest and most common method of assessing fixed nitrogen but in this research, different methods were explored in order to compare both qualitative and quantitative results. This review summarises the current knowledge related to Pongamia, rhizobia, nodulation and nitrogen fixation.

Gene Fitness of Azotobacter vinelandii Under Diazotrophic Growth

2021 ◽  
Author(s):  
Carolann M. Knutson ◽  
Meghan N. Pieper ◽  
Brett M. Barney
Keyword(s):  
Nitrogen Fixation ◽  
Azotobacter Vinelandii ◽  
Genetic Manipulation ◽  
Nitrogen Fixing ◽  
Obligate Aerobe ◽  
Dependent Growth ◽  
Metal Cofactors ◽  
Biological Nitrogen ◽  
Diazotrophic Growth ◽  
Reference Tool

Azotobacter vinelandii is a nitrogen-fixing free-living soil microbe that has been studied for decades in relation to biological nitrogen fixation (BNF). It is highly amenable to genetic manipulation, helping to unravel the intricate importance of different proteins involved in the process of BNF, including the biosynthesis of cofactors that are essential to assembling the complex metal cofactors that catalyze the difficult reaction of nitrogen fixation. Additionally, A. vinelandii accomplishes this feat while growing as an obligate aerobe, differentiating it from many of the nitrogen-fixing bacteria that are associated with plant roots. The ability to function in the presence of oxygen makes A. vinelandii suitable for application in various potential biotechnological schemes. In this study, we employed transposon sequencing (Tn-seq) to measure the fitness defects associated with disruptions of various genes under nitrogen-fixing dependent growth, versus growth with extraneously provided urea as a nitrogen source. The results allowed us to probe the importance of more than 3800 genes, revealing that many genes previously believed to be important, can be successfully disrupted without impacting cellular fitness. Importance These results provide insights into the functional redundancy in A. vinelandii , while also providing a direct measure of fitness for specific genes associated with the process of BNF. These results will serve as a valuable reference tool in future studies to uncover the mechanisms that govern this process.

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