NITROGEN FIXATION - SCI
& TECH
News: Can the newly discovered
organelle help engineer plants to fix nitrogen?
What's in the news?
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Two papers published recently, one in the
journal Science and another in the Cell, have generated new
interest in the endosymbiotic theory. The discovery concerns nitrogen fixation.
Nitrogen Fixation:
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Nitrogen is a key component in proteins and DNA of all living organisms.
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Although nitrogen gas makes up about 78% of the
Earth’s atmosphere by volume, plants and animals lack a system that can utilize
atmospheric nitrogen.
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Bacteria and archaea help convert atmospheric nitrogen gas to ammonia by
nitrogen fixation (or ammonification) to make nitrogen usable for
plants.
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This conversion process is collectively known as
“nitrogen fixation” and is limited to
certain bacteria with this specialized ability.
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Nitrogen fixation involves transforming the
relatively non-reactive atmospheric N2 into more reactive compounds, including
nitrates, nitrites, or ammonia.
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These reactive forms of nitrogen are vital for the
growth of crops, supporting their development and overall health.
Nitrogen-Fixing
Bacteria:
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These 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.
Types of Nitrogen Fixing
Bacteria:
There are two main types of nitrogen-fixing bacteria.
1. Symbiotic or
Mutualistic Bacteria:
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These species live in root nodules of certain plants. Plants of the pea family, known as
legumes which are some of the most important hosts for nitrogen-fixing
bacteria.
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Examples: Rhizobium, which is associated with
plants in the pea family and various Azospirillum species, which are associated
with cereal grasses.
2. Free-living Bacteria:
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Other nitrogen-fixing bacteria are free-living and do not require a host. They are
commonly found in soil or in aquatic environments.
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Examples: Cyanobacteria Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium.
Significance:
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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.
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Nitrogen-fixing bacteria accomplish more than 90
percent of all nitrogen fixation and thus play an important role in the
nitrogen cycle.
New Discovery:
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Unlike many free-living nitrogen-fixing bacteria,
legumes, a class of plants in the family Fabaceae,
bear the nitrogen-fixing bacteria in their root nodules.
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Ammonia is converted to nitrites and nitrates (nitrification) and then back into
atmospheric nitrogen (denitrification)
with the help of bacteria to complete the cycle.
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In marine environments, like on Earth, bacteria and
archaea are also involved in ammonification, nitrification, and
denitrification.
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Beyond mitochondria and chloroplasts, the current
discovery extends the earlier reports of a nitrogen-fixing cyanobacterium in
marine algae and establishes it as a new
organelle.
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The new organelle that the authors call nitroplast
co-evolved with its host cell.