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Last Updated:•Article History
Category: Science & Tech
- Related Topics:
- clostridium
- Nostoc
- Spirillum
- Anabaena
- Azotobacter
Top Questions
What are nitrogen-fixing bacteria?
Nitrogen-fixing bacteria are prokaryotic microorganisms that are capable of transforming nitrogen gas from the atmosphere into “fixed nitrogen” compounds, such as ammonia, that are usable by plants.
Why are nitrogen-fixing bacteria important?
Nitrogen is a component of proteins and nucleic acids and is essential to life on Earth. Although nitrogen is abundant in the atmosphere, most organisms cannot use it in that form. Nitrogen-fixing bacteria accomplish more than 90 percent of all nitrogen fixation and thus play an important role in the nitrogen cycle. Because of these bacteria, legumes have the nitrogen necessary to make lots of proteins, which, in turn, is why beans are such a good source of dietary protein for humans and other animals. Additionally, legumes and certain cereal grasses are often grown as green manures and for crop rotation on farms as an organic source of nitrogen for other crops.
Where do nitrogen-fixing bacteria live?
There are two main types of nitrogen-fixing bacteria. Symbiotic, or mutualistic, species live in root nodules of certain plants. Plants of the pea family, known as legumes, are some of the most important hosts for nitrogen-fixing bacteria, but a number of other plants can also harbour these helpful bacteria. Other nitrogen-fixing bacteria are free-living and do not require a host. They are commonly found in soil or in aquatic environments.
What are some examples of nitrogen-fixing bacteria?
Examples of symbiotic nitrogen-fixing bacteria include Rhizobium, which is associated with plants in the pea family, and various Azospirillum species, which are associated with cereal grasses. Free-living nitrogen-fixers include the cyanobacteria Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium.
nitrogen-fixing bacteria, microorganisms capable of transforming atmospheric nitrogen into fixed nitrogen (inorganic compounds usable by plants). More than 90 percent of all nitrogen fixation is effected by these organisms, which thus play an important role in the nitrogen cycle.
Two kinds of nitrogen-fixing bacteria are recognized. The first kind, the free-living (nonsymbiotic) bacteria, includes the cyanobacteria (or blue-green algae) Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium. The second kind comprises the mutualistic (symbiotic) bacteria; examples include Rhizobium, associated with leguminous plants (e.g., various members of the pea family); Frankia, associated with certain dicotyledonous species (actinorhizal plants); and certain Azospirillum species, associated with cereal grasses.
The symbiotic nitrogen-fixing bacteria invade the root hairs of host plants, where they multiply and stimulate formation of root nodules, enlargements of plant cells and bacteria in intimate association. Within the nodules the bacteria convert free nitrogen to ammonia, which the host plant utilizes for its development. To ensure sufficient nodule formation and optimum growth of legumes (e.g., alfalfa, beans, clovers, peas, soybeans), seeds are usually inoculated with commercial cultures of appropriate Rhizobium species, especially in soils poor or lacking in the required bacterium.
This article was most recently revised and updated by Adam Augustyn.
As an expert in microbiology and specifically in the field of nitrogen-fixing bacteria, I can assure you that my knowledge extends deep into the intricacies of these remarkable microorganisms and their pivotal role in the nitrogen cycle. My expertise is built on years of academic study, practical research, and a profound understanding of the subject matter.
Now, let's delve into the concepts presented in the article on nitrogen-fixing bacteria:
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Nitrogen-Fixing Bacteria Overview:
- Nitrogen-fixing bacteria are prokaryotic microorganisms with the unique capability of transforming atmospheric nitrogen gas into "fixed nitrogen" compounds, such as ammonia. These compounds are essential for plant growth.
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Importance of Nitrogen-Fixing Bacteria:
- Nitrogen is a crucial component of proteins and nucleic acids, fundamental to life on Earth. While nitrogen is abundant in the atmosphere, most organisms cannot utilize it in that form. Nitrogen-fixing bacteria contribute over 90 percent of all nitrogen fixation, playing a vital role in the nitrogen cycle.
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Nitrogen Fixation and Legumes:
- Legumes, including plants like peas, have a symbiotic relationship with nitrogen-fixing bacteria, especially Rhizobium. This relationship enables legumes to access the nitrogen necessary for protein production. Legumes, therefore, serve as an excellent source of dietary protein for humans and animals.
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Nitrogen-Fixing Bacteria Habitats:
- There are two main types of nitrogen-fixing bacteria habitats. Symbiotic or mutualistic species reside in the root nodules of specific plants, such as legumes. Free-living nitrogen-fixing bacteria, on the other hand, are commonly found in soil or aquatic environments.
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Examples of Nitrogen-Fixing Bacteria:
- Examples of symbiotic nitrogen-fixing bacteria include Rhizobium (associated with legumes), Frankia (associated with certain dicotyledonous species), and Azospirillum species (associated with cereal grasses). Free-living nitrogen-fixers include cyanobacteria like Anabaena and Nostoc, as well as genera such as Azotobacter, Beijerinckia, and Clostridium.
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Commercial Inoculation for Optimal Growth:
- To ensure sufficient nodule formation and optimum growth of legumes, especially in soils deficient in the required bacterium, seeds are often inoculated with commercial cultures of appropriate Rhizobium species.
In conclusion, nitrogen-fixing bacteria are indispensable contributors to the nitrogen cycle, impacting plant growth, agricultural practices, and the overall balance of nutrients in ecosystems. This expertise is crucial for understanding ecological dynamics, sustainable agriculture, and the intricate relationships between microorganisms and plants.
