Diazotroph

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Diazotrophs are bacteria and archaea that fix atmospheric nitrogen (N2) in the atmosphere into bioavailable forms such as ammonia.

Contents

A diazotroph is a microorganism that is able to grow without external sources of fixed nitrogen. Examples of organisms that do this are rhizobia and Frankia and Azospirillum . All diazotrophs contain iron-molybdenum or iron-vanadium nitrogenase systems. Two of the most studied systems are those of Klebsiella pneumoniae and Azotobacter vinelandii . These systems are studied because of their genetic tractability and their fast growth. [1]

Etymology

The word diazotroph is derived from the words diazo ("di" = two + "azo" = nitrogen) meaning "dinitrogen (N2)" and troph meaning "pertaining to food or nourishment", in summary dinitrogen utilizing. The word azote means nitrogen in French and was named by French chemist and biologist Antoine Lavoisier, who saw it as the part of air which cannot sustain life. [2]

Types

Diazotrophs are scattered across Bacteria taxonomic groups (as well as a couple of Archaea). Even within a species that can fix nitrogen there may be strains that do not. [3] Fixation is shut off when other sources of nitrogen are available, and, for many species, when oxygen is at high partial pressure. Bacteria have different ways of dealing with the debilitating effects of oxygen on nitrogenases, listed below.

Free-living diazotrophs

Symbiotic diazotrophs

Cultivation

Under the laboratory conditions, extra nitrogen sources are not needed to grow free-living diazotrophs. Carbon sources (such as sucrose or glucose) and a small amount of inorganic salt are added to the medium. Free-living diazotrophs can directly use atmospheric nitrogen (N2). However, while cultivating several symbiotic diazotrophs, such as rhizobia, it is necessary to add nitrogen because rhizobia and other symbiotic nitrogen-fixing bacteria can not use molecular nitrogen (N2) in free-living form and only fix nitrogen during symbiosis with a host plant. [11]

Application

Biofertilizer

Diazotroph fertilizer is a kind of biofertilizer that can use nitrogen-fixing microorganisms to convert molecular nitrogen (N2) into ammonia (which is the formation of nitrogen available for the crops to use). These nitrogen nutrients then can be used in the process of protein synthesis for the plants. This whole process of nitrogen fixation by diazotroph is called biological nitrogen fixation. This biochemical reaction can be carried out under normal temperature and pressure conditions. So it does not require extreme conditions and specific catalysts in fertilizer production. Therefore, produce available nitrogen in this way can be cheap, clean and efficient. Nitrogen-fixing bacteria fertilizer is an ideal and promising biofertilizer. [12]

From the ancient time, people grow the leguminous crops to make the soil more fertile. And the reason for this is: the root of leguminous crops are symbiotic with the rhizobia (a kind of diazotroph). These rhizobia can be considered as a natural biofertilizer to provide available nitrogen in the soil. After harvesting the leguminous crops, and then grow other crops (may not be leguminous), they can also use these nitrogen remain in the soil and grow better.

Leguminous plants used to fertilize an abandoned land Leguminous plant by MG.jpg
Leguminous plants used to fertilize an abandoned land

Diazotroph biofertilizers used today include Rhizobium, Azotobacter, Azospirilium and Blue green algae (a genus of cyanobacteria). These fertilizer are widely used and commenced into industrial production. So far in the market, nitrogen fixation biofertilizer can be divided into liquid fertilizer and solid fertilizer. Most of the fertilizers are fermented in the way of liquid fermentation. After fermentation, the liquid bacteria can be packaged, which is the liquid fertilizer, and the fermented liquid can also be adsorbed with sterilized peat and other carrier adsorbents to form a solid microbial fertilizer. These nitrogen-fixation fertilizer has a certain effect on increasing the production of cotton, rice, wheat, peanuts, rape, corn, sorghum, potatoes, tobacco, sugarcane and various vegetables.

Importance

In organisms the symbiotic associations greatly exceed the free-living species, with the exception of cyanobacteria. [3]

Biologically available nitrogen such as ammonia is the primary limiting factor for life on earth. Diazotroph plays an important roles in nitrogen cycle of the earth. In the terrestrial ecosystem, the diazotroph fix the (N2) from the atmosphere and provide the available nitrogen for the primary producer. Then the nitrogen is transferred to higher trophical levels and human beings. The formation and storage of nitrogen will all influenced by the transformation process. Also the available nitrogen fixed by the diazotroph is environmentally sustainable, which can reduce the use of fertilizer, which can be an important topic in agricultural research.

In marine ecosystem, prokaryotic phytoplankton (such as cyanobacteria) is the main nitrogen fixer, then the nitrogen consumed by higher trophical levels. The fixed N released from these organisms is a component of ecosystem N inputs. And also the fixed N is important for the coupled C cycle. A greater oceanic inventory of fixed N may increase the primary production and export of organic C to the deep ocean. [13] [14]

Related Research Articles

Nitrogen fixation is a chemical process by which molecular dinitrogen is converted into ammonia. It occurs both biologically and abiologically in chemical industries. Biological nitrogen fixation or diazotrophy is catalyzed by enzymes called nitrogenases. These enzyme complexes are encoded by the Nif genes and contain iron, often with a second metal.

<span class="mw-page-title-main">Leghemoglobin</span> Oxygen-carrying phytoglobin found in rhizome of leguminous plants

Leghemoglobin is an oxygen-carrying phytoglobin found in the nitrogen-fixing root nodules of leguminous plants. It is produced by these plants in response to the roots being colonized by nitrogen-fixing bacteria, termed rhizobia, as part of the symbiotic interaction between plant and bacterium: roots not colonized by Rhizobium do not synthesise leghemoglobin. Leghemoglobin has close chemical and structural similarities to hemoglobin, and, like hemoglobin, is red in colour. It was originally thought that the heme prosthetic group for plant leghemoglobin was provided by the bacterial symbiont within symbiotic root nodules. However, subsequent work shows that the plant host strongly expresses heme biosynthesis genes within nodules, and that activation of those genes correlates with leghemoglobin gene expression in developing nodules.

<span class="mw-page-title-main">Rhizobia</span> Nitrogen fixing soil bacteria

Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. In general, they are gram negative, motile, non-sporulating rods.

<i>Trichodesmium</i> Genus of bacteria

Trichodesmium, also called sea sawdust, is a genus of filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters. Trichodesmium is a diazotroph; that is, it fixes atmospheric nitrogen into ammonium, a nutrient used by other organisms. Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts.

<span class="mw-page-title-main">Heterocyst</span>

Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as Nostoc, Cylindrospermum, and Anabaena. They fix nitrogen from dinitrogen (N2) in the air using the enzyme nitrogenase, in order to provide the cells in the filament with nitrogen for biosynthesis.

<span class="mw-page-title-main">Root nodule</span> Plant part

Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as rhizobia. This process has evolved multiple times within the legumes, as well as in other species found within the Rosid clade. Legume crops include beans, peas, and soybeans.

<span class="mw-page-title-main">Nitrogenase</span> Class of enzymes

Nitrogenases are enzymes (EC 1.18.6.1EC 1.19.6.1) that are produced by certain bacteria, such as cyanobacteria (blue-green bacteria) and rhizobacteria. These enzymes are responsible for the reduction of nitrogen (N2) to ammonia (NH3). Nitrogenases are the only family of enzymes known to catalyze this reaction, which is a step in the process of nitrogen fixation. Nitrogen fixation is required for all forms of life, with nitrogen being essential for the biosynthesis of molecules (nucleotides, amino acids) that create plants, animals and other organisms. They are encoded by the Nif genes or homologs. They are related to protochlorophyllide reductase.

<i>Frankia</i> Genus of bacteria

Frankia is a genus of nitrogen-fixing bacteria that live in symbiosis with actinorhizal plants, similar to the Rhizobium bacteria found in the root nodules of legumes in the family Fabaceae. Frankia also initiate the forming of root nodules.

<i>Azotobacter</i> Genus of bacteria

Azotobacter is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes that play an important role in the nitrogen cycle in nature, binding atmospheric nitrogen, which is inaccessible to plants, and releasing it in the form of ammonium ions into the soil. In addition to being a model organism for studying diazotrophs, it is used by humans for the production of biofertilizers, food additives, and some biopolymers. The first representative of the genus, Azotobacter chroococcum, was discovered and described in 1901 by Dutch microbiologist and botanist Martinus Beijerinck. Azotobacter species are Gram-negative bacteria found in neutral and alkaline soils, in water, and in association with some plants.

Azotobacter vinelandii is Gram-negative diazotroph that can fix nitrogen while grown aerobically. These bacteria are easily cultured and grown.

<i>Bradyrhizobium</i> Genus of bacteria

Bradyrhizobium is a genus of Gram-negative soil bacteria, many of which fix nitrogen. Nitrogen fixation is an important part of the nitrogen cycle. Plants cannot use atmospheric nitrogen (N2); they must use nitrogen compounds such as nitrates.

The nif genes are genes encoding enzymes involved in the fixation of atmospheric nitrogen into a form of nitrogen available to living organisms. The primary enzyme encoded by the nif genes is the nitrogenase complex which is in charge of converting atmospheric nitrogen (N2) to other nitrogen forms such as ammonia which the organism can use for various purposes. Besides the nitrogenase enzyme, the nif genes also encode a number of regulatory proteins involved in nitrogen fixation. The nif genes are found in both free-living nitrogen-fixing bacteria and in symbiotic bacteria associated with various plants. The expression of the nif genes is induced as a response to low concentrations of fixed nitrogen and oxygen concentrations (the low oxygen concentrations are actively maintained in the root environment of host plants). The first Rhizobium genes for nitrogen fixation (nif) and for nodulation (nod) were cloned in the early 1980s by Gary Ruvkun and Sharon R. Long in Frederick M. Ausubel's laboratory.

Actinorhizal plants are a group of angiosperms characterized by their ability to form a symbiosis with the nitrogen fixing actinomycetota Frankia. This association leads to the formation of nitrogen-fixing root nodules.

Cyanobionts are cyanobacteria that live in symbiosis with a wide range of organisms such as terrestrial or aquatic plants; as well as, algal and fungal species. They can reside within extracellular or intracellular structures of the host. In order for a cyanobacterium to successfully form a symbiotic relationship, it must be able to exchange signals with the host, overcome defense mounted by the host, be capable of hormogonia formation, chemotaxis, heterocyst formation, as well as possess adequate resilience to reside in host tissue which may present extreme conditions, such as low oxygen levels, and/or acidic mucilage. The most well-known plant-associated cyanobionts belong to the genus Nostoc. With the ability to differentiate into several cell types that have various functions, members of the genus Nostoc have the morphological plasticity, flexibility and adaptability to adjust to a wide range of environmental conditions, contributing to its high capacity to form symbiotic relationships with other organisms. Several cyanobionts involved with fungi and marine organisms also belong to the genera Richelia, Calothrix, Synechocystis, Aphanocapsa and Anabaena, as well as the species Oscillatoria spongeliae. Although there are many documented symbioses between cyanobacteria and marine organisms, little is known about the nature of many of these symbioses. The possibility of discovering more novel symbiotic relationships is apparent from preliminary microscopic observations.

<span class="mw-page-title-main">Biofertilizer</span> Substance with micro-organisms

A biofertilizer is a substance which contains living micro-organisms which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Biofertilizers add nutrients through the natural processes of nitrogen fixation, solubilizing phosphorus, and stimulating plant growth through the synthesis of growth-promoting substances. The micro-organisms in biofertilizers restore the soil's natural nutrient cycle and build soil organic matter. Through the use of biofertilizers, healthy plants can be grown, while enhancing the sustainability and the health of the soil. Biofertilizers can be expected to reduce the use of synthetic fertilizers and pesticides, but they are not yet able to replace their use. Since they play several roles, a preferred scientific term for such beneficial bacteria is "plant-growth promoting rhizobacteria" (PGPR).

Agricultural microbiology is a branch of microbiology dealing with plant-associated microbes and plant and animal diseases. It also deals with the microbiology of soil fertility, such as microbial degradation of organic matter and soil nutrient transformations. The primary goal of agricultural microbiology is to comprehensively explore the interactions between beneficial microorganisms like bacteria and fungi with crops. It also deals with the microbiology of soil fertility, such as microbial degradation of organic matter and soil nutrient transformations.

<i>Frankia alni</i> Species of bacterium

Frankia alni is a Gram-positive species of actinomycete filamentous bacterium that lives in symbiosis with actinorhizal plants in the genus Alnus. It is a nitrogen-fixing bacterium and forms nodules on the roots of alder trees.

Raphidiopsis raciborskii is a freshwater cyanobacterium.

A nitrogen fixation package is a piece of research equipment for studying nitrogen fixation in plants. One product of this kind, the Q-Box NF1LP made by Qubit Systems, operates by measuring the hydrogen (H2) given off in the nitrogen-fixing chemical reaction enabled by nitrogenase enzymes.

Richelia is a genus of nitrogen-fixing, filamentous, heterocystous and cyanobacteria. It contains the single species Richelia intracellularis. They exist as both free-living organisms as well as symbionts within potentially up to 13 diatoms distributed throughout the global ocean. As a symbiont, Richelia can associate epiphytically and as endosymbionts within the periplasmic space between the cell membrane and cell wall of diatoms.

References

  1. Dixon R, Kahn D (August 2004). "Genetic regulation of biological nitrogen fixation". Nature Reviews. Microbiology. 2 (8): 621–31. doi:10.1038/nrmicro954. PMID   15263897. S2CID   29899253.
  2. "Diazotroph - Biology-Online Dictionary | Biology-Online Dictionary". Archived from the original on 2017-03-15. Retrieved 2017-04-05.
  3. 1 2 3 4 5 6 7 8 9 10 11 Postgate, J (1998). Nitrogen Fixation, 3rd Edition. Cambridge University Press, Cambridge UK.
  4. Bae HS, Morrison E, Chanton JP, Ogram A (April 2018). "Methanogens Are Major Contributors to Nitrogen Fixation in Soils of the Florida Everglades". Applied and Environmental Microbiology. 84 (7): e02222–17. Bibcode:2018ApEnM..84E2222B. doi:10.1128/AEM.02222-17. PMC   5861825 . PMID   29374038.
  5. Zehr JP (April 2011). "Nitrogen fixation by marine cyanobacteria". Trends in Microbiology. 19 (4): 162–73. doi:10.1016/j.tim.2010.12.004. PMID   21227699.
  6. Bergman B, Sandh G, Lin S, Larsson J, Carpenter EJ (May 2013). "Trichodesmium--a widespread marine cyanobacterium with unusual nitrogen fixation properties". FEMS Microbiology Reviews. 37 (3): 286–302. doi:10.1111/j.1574-6976.2012.00352.x. PMC   3655545 . PMID   22928644.
  7. Blankenship RE, Madigan MT & Bauer CE (1995). Anoxygenic photosynthetic bacteria. Dordrecht, The Netherlands, Kluwer Academic.
  8. 1 2 3 Vessey JK, Pawlowski, K and Bergman B (2005). "Root-based N2-fixing symbioses: Legumes, actinorhizal plants, Parasponia sp and cycads". Plant and Soil. 274 (1–2): 51–78. doi:10.1007/s11104-005-5881-5. S2CID   5035264.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. Beckwith J, Tjepkema JD, Cashon RE, Schwintzer CR, Tisa LS (December 2002). "Hemoglobin in five genetically diverse Frankia strains". Canadian Journal of Microbiology. 48 (12): 1048–55. doi:10.1139/w02-106. PMID   12619816.
  10. Soltis DE, Soltis PS, Morgan DR, Swensen SM, Mullin BC, Dowd JM, Martin PG (March 1995). "Chloroplast gene sequence data suggest a single origin of the predisposition for symbiotic nitrogen fixation in angiosperms". Proceedings of the National Academy of Sciences of the United States of America. 92 (7): 2647–51. Bibcode:1995PNAS...92.2647S. doi: 10.1073/pnas.92.7.2647 . PMC   42275 . PMID   7708699.
  11. Somasegaran, Padma; Hoden, Heinz.J (1994). Handbook for Rhizobia (1 ed.). New York, NY: Springer. p. 1. doi:10.1007/978-1-4613-8375-8. ISBN   978-1-4613-8375-8. S2CID   21924709.
  12. Vessey, J.K. (2003). "Plant growth promoting rhizobacteria as biofertilizers". Plant and Soil. 255 (2): 571–586. doi:10.1023/A:1026037216893. S2CID   37031212.
  13. Inomura, Keisuke; Deutsch, Curtis; Masuda, Takako; Prášil, Ondrej; Follows, Michael J. (2020). "Quantitative models of nitrogen-fixing organisms". Computational and Structural Biotechnology. 18: 3905–3924. doi:10.1016/j.csbj.2020.11.022. PMC   7733014 . PMID   33335688.
  14. Karl, David M.; Church, Matthew J.; Dore, John E.; Letelier, Richardo M.; Mahaffey, Claire (2012). "Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation". PNAS. 109 (6): 1842–1849. doi: 10.1073/pnas.1120312109 . PMC   3277559 . PMID   22308450.