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Explora: Environment
and Resource Anabaena-Azolla for crops and bioenergy

elevated CO , as evidenced by a significant increase of their surrounding environment in their fixed form, and
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chlorophyll A and B, as well as carotenoids. The application not as molecular nitrogen. The ultimate final product of
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of Azolla with inorganic compost helps decrease CO levels the converted nitrogen is the formation of amino acids,
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in the environment through photosynthesis while adding the constituents of proteins. 42
stable, humified materials to the soil without compromising
grain efficiency. Grain yield increased by 27% with the 5.2. Biological nitrogen fixation and its regulation
combination of nitrogen-phosphorus-potassium (NPK) The biological fixation of nitrogen is the catalytic
and Azolla fertilizer when compared to the control. 35 reduction of dinitrogen into NH in the presence of an
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enzyme called nitrogenase. This process is carried out
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5. Role of nitrogen in life forms by diazotrophic microorganisms, which can be either
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Nitrogen is a crucial element that supports all life forms. symbiotic or non-symbiotic. The nitrogenase enzyme
Naturally, it is found in proteins and amino acids, as well is composed of two components, namely dinitrogenase
as in other organic compounds derived from the nitrogen (iron-molybdenum) and dinitrogenase reductase
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fixation process. Nitrogen is the most abundant gas in the (iron [Fe]). The dinitrogenase reductase contains two
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atmosphere. Prokaryotic organisms, which can be either identical subunits, which are encoded by nifH genes,
free-living or symbiotic, are the only ones capable of whereas dinitrogenase has four subunits, where nifD
carrying out the biological nitrogen fixation process. An genes encode two identical α subunits and nifK genes
organism’s capacity to fix nitrogen is strongly influenced encode two similar subunits. The energy for this reaction
by the amount of oxygen (O ) present in the surrounding is provided by the breakdown of adenosine triphosphate
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air, carbon substrates, and favorable moisture conditions. (ATP, derived from photosynthesis), and electrons
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Even though nitrogen is necessary for plant growth, no are transferred from ferredoxin or flavodoxin. For the
plant species can convert N into NH , which would allow assimilation of fixed nitrogen into NH , three enzymes
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2
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them to grow. Therefore, the symbiont residing inside the are present in the heterocyst: glutamine synthetase,
plant must accomplish the task. 35 glutamate dehydrogenase, and glutamate synthetase. The
distribution of fixed nitrogen in Azollae-Anabaena has
5.1. Nitrogen metabolism and cyanobacteria been found in four different forms, such as intracellular
Most cyanobacteria are free-living, nitrogen-fixing NH , extracellular NH , intracellular organic nitrogen,
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organisms. Heterocysts, a particular type of nitrogen- and extracellular organic nitrogen.
fixing cell, are responsible for this. 37,38 Cyanobacteria The nitrogen fixation process needs a high amount of
come in several forms, including unicellular, colonial, energy to break down the triple bond of dinitrogen and
branching, unbranched filamentous, pseudo- convert it into NH . This entire process is illustrated in
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parenchymatous, heterocystous, and heterotrichous- Figure 2. The energy source, ATP formation, requires O ,
2
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heterocystous. Cyanobacteria are divided into three but the nitrogenase enzyme can be inhibited by even a trace
types based on their ability to fix nitrogen dioxide: amount of it. This is why the heterocyst (where nitrogen
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unicellular, filamentous non-heterocystous, and fixation takes place) does not contain any pigment, and
filamentous heterocystous. The heterocystous forms fix thus, no photosynthesis/energy production occurs. 48,49 This
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nitrogen under aerobic conditions, whereas the non- process is also regulated by the molecular level. Certain nif
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heterocystous forms have developed the ability to fix genes are transcriptionally regulated by nifA. A negative
nitrogen in anaerobic environments. In cultivated rice regulator, nifL, interacts with nifA to provide signals to
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fields, cyanobacteria are the main source of nitrogen- the nitrogenase enzyme about environmental stressors.
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fixing biomass. The significance of cyanobacteria in In addition to the regulation by the cyanobiont, plants
rice fields is directly tied to their favorable impact on also regulate the process of nitrogen fixation, including
plants and crops. Anabaena spp. and Nostoc spp. are the the signaling between the cyanobacteria and the plant, as
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most common nitrogen-fixing organisms in rice fields, well as their exchange of nutrients and nitrogen during the
typically manifesting as free-floating water blooms that period of symbiosis. 50
create microbial mats. Nitrogen is a crucial element
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widely found in various biochemical compounds such 5.3. Detailed mechanism of nitrogen fixation
as nucleotides, and proteins, which are present in The entire class of nitrogen-fixing cyanobacteria (including
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the cells of all living organisms. The incorporation of both heterocystous and non-heterocystous filamentous/
nitrogen within a food chain occurs due to the activity unicellular forms) is capable of using molecular nitrogen as
of photoautotrophic organisms such as plants, algae, and a source of nitrogen. Nitrogenase is an enzyme complex
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cyanobacteria. These autotrophs take up nitrogen from that converts dinitrogen to NH , a process that requires
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Volume 2 Issue 2 (2025) 4 doi: 10.36922/eer.7975