Environmental and Economic Impacts of Biological Nitrogen-Fixing (BNF) Cereal Crops

Agricultural yields are often limited by nitrogen (N) availability, especially in countries of the developing world, whereas in industrialized nations the application of chemical N fertilizers has reached unsustainable levels that have resulted in severe environmental consequences. Finding alternatives to inorganic fertilizers is critical for sustainable and secure food production. Although gaseous nitrogen (N2) is abundant in the atmosphere, it cannot be assimilated by most living organisms. Only a selected group of microorganisms termed diazotrophs, have evolved the ability to reduce N2 to generate NH3 in a process known as biological nitrogen fixation (BNF) catalysed by nitrogenase, an oxygen-sensitive enzyme complex. This ability presents an opportunity to improve the nutrition of crop plants, through the introduction into cereal crops of either the N fixing bacteria or the nitrogenase enzyme responsible for N fixation. This review explores three potential approaches to obtain N-fixing cereals: (a) engineering the nitrogenase enzyme to function in plant cells; (b) engineering the legume symbiosis into cereals; and (c) engineering cereals with the capability to associate with N-fixing bacteria.

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Inoculation with Different Nitrogen-Fixing Bacteria and Arbuscular Mycorrhiza Affects Grain Protein Content and Nodule Bacterial Communities of a Fava Bean Crop

Agronomy ◽

10.3390/agronomy10060768 ◽

2020 ◽

Vol 10 (6) ◽

pp. 768

Author(s):

Virginia Sánchez-Navarro ◽

Raúl Zornoza ◽

Ángel Faz ◽

Catalina Egea-Gilabert ◽

Margarita Ros ◽

...

Keyword(s):

Protein Content ◽

Crop Yield ◽

Rhizobium Leguminosarum ◽

Grain Protein Content ◽

Grain Protein ◽

Nitrogen Fixing ◽

Nitrogen Fixing Bacteria ◽

Yield And Quality ◽

Biological Nitrogen ◽

Bean Crop

The introduction of nitrogen fixing bacteria (NFB) and arbuscular mycorrhizal fungi (AMF) into the soil is an advisable agricultural practice for the crop, since it enhances nutrient and water uptake and tolerance to biotic and abiotic stresses. The aim of this work was to study plant nutrition, biological nitrogen fixation (BNF) and crop yield and quality, after inoculating seeds with NFBs ((Rhizobium leguminosarum, Burkholderia cenocepacia, Burkholderia vietnamiensis)) and/or AMFs (Rhizophagus irregularis, Claroideoglomus etunicatum, Claroideoglomus claroideum and Funneliformis mosseae) in a fava bean crop in two seasons. The composition of the nodule bacterial community was evaluated by the high-throughput sequencing analysis of bacterial 16 S rRNA genes. It was found that microbial inoculation accompanied by a 20% decrease in mineral fertilization had no significant effect on crop yield or the nutritional characteristics compared with a non-inoculated crop, except for an increase in the grain protein content in inoculated plants. None of the inoculation treatments increased biological nitrogen fixation over a non-inoculated level. The bacterial rRNA analysis demonstrated that the genus Rhizobium predominated in all nodules, both in inoculated and non-inoculated treatments, suggesting the previous presence of these bacteria in the soil. In our study, inoculation with Rhizobium leguminosarum was the most effective treatment for increasing protein content in seeds, while Burkholderia sp. was not able to colonise the plant nodules. Inoculation techniques used in fava beans can be considered an environmentally friendly alternative, reducing the input of fertilizers, while maintaining crop yield and quality, with the additional benefit of increasing the grain protein content. However, further research is required on the selection and detection of efficient rhizobial strains under local field conditions, above all those related to pH and soil type, in order to achieve superior nitrogen-fixing bacteria.

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Biological nitrogen fixing capacity and biomass production of different understorey pastures in a Pinus radiata-pasture agroforestry system in New Zealand

Agroforestry Systems ◽

10.1007/bf00129631 ◽

1996 ◽

Vol 34 (1) ◽

pp. 33-49 ◽

Cited By ~ 29

Author(s):

K. M. Goh ◽

I. Mansur ◽

D. J. Mead ◽

G. B. Sweet

Keyword(s):

New Zealand ◽

Biomass Production ◽

Pinus Radiata ◽

Agroforestry System ◽

Nitrogen Fixing ◽

Biological Nitrogen

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The Leeuwenhoek Lecture, 1992 Bacterial evolution and the nitrogen-fixing plant

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1992.0158 ◽

1992 ◽

Vol 338 (1286) ◽

pp. 409-416 ◽

Cited By ~ 12

Keyword(s):

Nitrogen Fixation ◽

Biological Nitrogen Fixation ◽

Bacterial Species ◽

Nitrogen Fixing ◽

Bacterial Evolution ◽

Late Emergence ◽

Biological Nitrogen

Biological nitrogen fixation is fundamental to the economy of the biosphere, yet it is restricted to a few dozen bacterial species. Why have plants not acquired it during evolution? No serious physiological or genetic obstacles seem to exist. Has a relatively late emergence, among genomically flexible prokaryotes, effectively precluded appropriate seletion pressure?

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Evolution of nitrogen-fixing symbioses

Proceedings of the Royal Society of Edinburgh Section B Biological Sciences ◽

10.1017/s0269727000004036 ◽

1985 ◽

Vol 85 (3-4) ◽

pp. 215-237 ◽

Cited By ~ 17

Author(s):

J. I. Sprent ◽

J. A. Raven

Keyword(s):

Root Nodules ◽

Land Plants ◽

Oxygenic Photosynthesis ◽

Ecological Niches ◽

Energy Costs ◽

Nitrogen Fixing ◽

Infection Structure ◽

Combined Nitrogen ◽

High Level ◽

Biological Nitrogen

SynopsisBecause of both the energy costs and the slowness of the reactions of the nitrogenase complex compared with those involving some form of combined nitrogen (oxidised or reduced), we argue that the evolution of nitrogen-fixing organisms required an environment which was very limited in combined nitrogen. This is thought to have occurred after phototrophy evolved, but before water was used as a hydrogen donor (and therefore oxygen was present in the atmosphere). After oxygenic photosynthesis evolved, the need for a high level of biological nitrogen-fixation remained, since abiotic inputs were insufficient to keep pace with the rapidly evolving biomass (flora and fauna). Symbiotic fixation probably first evolved in the form of casual associations between cyanobacteria and most other groups of plants. By inhabiting the sporophytic generation of evolving land plants (cycads in particular), protection against nitrogenase-inactivating oxygen and a more desiccating environment was achieved simultaneously.We envisage nodulated plants arising by the transfer ofnifgenes into tumour-forming bacteria. In the case of legumes, these would be ancestors of extant agrobacteria, which gain entry into their hostsviawounds. Co-evolution of symbionts from nitrogen-fixing tumours has taken several routes, leading to extant nodules differing in mode of infection, structure and physiology. Evolution towards optimisation of oxygen usage is continuing.Nitrogen-fixing symbiosis in animal systems is only advantageous in specialised ecological niches in which wood is the sole dietary intake. In the case of shipworms, the symbiosis has many of the advanced features associated with nitrogen fixing root nodules.

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Yield Increases in Summer Cereal Crops in Israeli Fields Inoculated with Azospirillum

Experimental Agriculture ◽

10.1017/s0014479700011431 ◽

1981 ◽

Vol 17 (2) ◽

pp. 179-187 ◽

Cited By ~ 54

Author(s):

Y. Kapulnik ◽

S. Sarig ◽

I. Nur ◽

Y. Okon ◽

J. Kigel ◽

...

Keyword(s):

Zea Mays ◽

Sorghum Bicolor ◽

Nitrogen Fertilizer ◽

Field Experiments ◽

Setaria Italica ◽

Cereal Crops ◽

Nitrogen Fixing ◽

Panicum Miliaceum ◽

Nitrogen Fixing Bacteria ◽

Commercial Value

SUMMARYInoculatingZea mays(three cultivars),Sorghum bicolor, Panicum miliaceumandSetaria italicawith nitrogen-fixing bacteria of the genus Azospirillum in Northern Negev and Bet Shean Valley field experiments resulted in significant increases in yield of grain and foliage of commercial value. It was concluded that inoculating summer cereal crops in Israel may save valuable nitrogen fertilizer.

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Biological Nitrogen Fixation in the Context of Global Change

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-12-12-0293-cr ◽

2013 ◽

Vol 26 (5) ◽

pp. 486-494 ◽

Cited By ~ 85

Author(s):

José Olivares ◽

Eulogio J. Bedmar ◽

Juan Sanjuán

Keyword(s):

Nitrogen Fixation ◽

Biological Nitrogen Fixation ◽

Food Production ◽

Agricultural Practices ◽

N Fertilization ◽

Agricultural Crops ◽

Nitrogen Fixing ◽

Sustainable Technologies ◽

Use Efficiency ◽

Biological Nitrogen

The intensive application of fertilizers during agricultural practices has led to an unprecedented perturbation of the nitrogen cycle, illustrated by the growing accumulation of nitrates in soils and waters and of nitrogen oxides in the atmosphere. Besides increasing use efficiency of current N fertilizers, priority should be given to value the process of biological nitrogen fixation (BNF) through more sustainable technologies that reduce the undesired effects of chemical N fertilization of agricultural crops. Wider legume adoption, supported by coordinated legume breeding and inoculation programs are approaches at hand. Also available are biofertilizers based on microbes that help to reduce the needs of N fertilization in important crops like cereals. Engineering the capacity to fix nitrogen in cereals, either by themselves or in symbiosis with nitrogen-fixing microbes, are attractive future options that, nevertheless, require more intensive and internationally coordinated research efforts. Although nitrogen-fixing plants may be less productive, at some point, agriculture must significantly reduce the use of warming (chemically synthesized) N and give priority to BNF if it is to sustain both food production and environmental health for a continuously growing human population.

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Understanding plant-root interactions with rhizobacteria to improve biological nitrogen fixation in crops

Understanding and improving crop root function - Burleigh Dodds Series in Agricultural Science ◽

10.19103/as.2020.0075.09 ◽

2021 ◽

pp. 163-194

Author(s):

Ulrike Mathesius ◽

◽

Jian Jin ◽

Yansheng Li ◽

Michelle Watt ◽

...

Keyword(s):

Nitrogen Fixation ◽

Biological Nitrogen Fixation ◽

Plant Root ◽

Current Understanding ◽

Plant Roots ◽

Nitrogen Fixing ◽

Root Interactions ◽

Molecular Determinants ◽

Abiotic Constraints ◽

Biological Nitrogen

Plant roots have evolved with the presence of rhizobacteria that can colonise the surface or interior of the plant. Some of these rhizobacteria are actively recruited by the plant and carry out particular functions, in particular in nutrient acquisition. Nitrogen-fixing bacteria form associations with many plant species, either as external associations or as symbiotic endophytes. The symbiosis between legumes and nitrogen-fixing rhizobia has been studied in most detail and is the most important contributor to nitrogen fixation in agriculture. This chapter highlights our current understanding of the molecular determinants of legume nodulation as well as challenges for improvements of biological nitrogen fixation in legumes and non-legumes. There is a need for connecting out knowledge of the molecular regulation of nodulation with field-based studies that take into account the interaction of nodulation with biotic and abiotic constraints. In addition, current approaches for engineering new symbioses are discussed.

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Transcriptional Analysis of an Ammonium-Excreting Strain of Azotobacter vinelandii Deregulated for Nitrogen Fixation

Applied and Environmental Microbiology ◽

10.1128/aem.01534-17 ◽

2017 ◽

Vol 83 (20) ◽

Cited By ~ 10

Author(s):

Brett M. Barney ◽

Mary H. Plunkett ◽

Velmurugan Natarajan ◽

Florence Mus ◽

Carolann M. Knutson ◽

...

Keyword(s):

Nitrogen Fixation ◽

Stationary Phase ◽

Gene Transcription ◽

Biological Nitrogen Fixation ◽

Azotobacter Vinelandii ◽

Nitrogen Fixing ◽

Wild Type ◽

Content Type ◽

Ammonium Production ◽

Biological Nitrogen

ABSTRACT Biological nitrogen fixation is accomplished by a diverse group of organisms known as diazotrophs and requires the function of the complex metalloenzyme nitrogenase. Nitrogenase and many of the accessory proteins required for proper cofactor biosynthesis and incorporation into the enzyme have been characterized, but a complete picture of the reaction mechanism and key cellular changes that accompany biological nitrogen fixation remain to be fully elucidated. Studies have revealed that specific disruptions of the antiactivator-encoding gene nifL result in the deregulation of the nif transcriptional activator NifA in the nitrogen-fixing bacterium Azotobacter vinelandii, triggering the production of extracellular ammonium levels approaching 30 mM during the stationary phase of growth. In this work, we have characterized the global patterns of gene expression of this high-ammonium-releasing phenotype. The findings reported here indicated that cultures of this high-ammonium-accumulating strain may experience metal limitation when grown using standard Burk's medium, which could be amended by increasing the molybdenum levels to further increase the ammonium yield. In addition, elevated levels of nitrogenase gene transcription are not accompanied by a corresponding dramatic increase in hydrogenase gene transcription levels or hydrogen uptake rates. Of the three potential electron donor systems for nitrogenase, only the rnf1 gene cluster showed a transcriptional correlation to the increased yield of ammonium. Our results also highlight several additional genes that may play a role in supporting elevated ammonium production in this aerobic nitrogen-fixing model bacterium. IMPORTANCE The transcriptional differences found during stationary-phase ammonium accumulation show a strong contrast between the deregulated (nifL-disrupted) and wild-type strains and what was previously reported for the wild-type strain under exponential-phase growth conditions. These results demonstrate that further improvement of the ammonium yield in this nitrogenase-deregulated strain can be obtained by increasing the amount of available molybdenum in the medium. These results also indicate a potential preference for one of two ATP synthases present in A. vinelandii as well as a prominent role for the membrane-bound hydrogenase over the soluble hydrogenase in hydrogen gas recycling. These results should inform future studies aimed at elucidating the important features of this phenotype and at maximizing ammonium production by this strain.

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