How can we say cynobacteria as photosynthtic if it fix atmospheric nitrogen ??
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cynobacteria are oxygenic photosynthetic bacteria that are widespread in marine, freshwater and terrestrial environments, and many of them are capable of fixing atmospheric nitrogen. However, ironically, nitrogenase, the enzyme that is responsible for the reduction of N2, is extremely sensitive to O2. Therefore, oxygenic photosynthesis and N2 fixation are not compatible. Hence, cyanobacteria had to evolve a variety of strategies circumventing this paradox, allowing them to grow at the expense of N2, a ubiquitous source of nitrogen. Some filamentous cyanobacteria differentiate heterocysts. These cells lack the oxygenic photosystem and possess a glycolipid cell wall that keeps the oxygen concentration sufficiently low for nitrogen fixation to take place. This strategy is known as spatial separation of oxygenic photosynthesis and nitrogen fixation. Nonheterocystous cyanobacteria may temporally separate these processes by fixing nitrogen during the night. Again others use a combination of these strategies.
KEY CONCEPTS
Cyanobacteria may fix the ubiquitously available CO2 and N2, and therefore cover the demand of the two most important elements.
The fixation of N2 comes at a high metabolic energy cost, but cyanobacteria are phototrophic organisms that use sunlight to cover their energy demand.
Nitrogenase, the enzyme complex responsible for the fixation of N2, is sensitive to oxygen and requires a near‐to‐anoxic environment.
Cyanobacteria are phototrophic organisms evolving oxygen and they developed various strategies to combine this with N2 fixation.
In order to fix N2, cyanobacteria separate the incompatible processes of oxygenic photosynthesis and N2 fixation spatially (in different cells) or temporally (during the night), or a combination of both.
N2 fixation in the ocean is restricted to the (sub)tropics and carried out by free‐living nonheterocystous filamentous and unicellular cyanobacteria and by symbiotic cyanobacteria living with microalgae.
Heterocystous cyanobacteria are found in freshwater, brackish water, terrestrial environments and symbiotic in plants and algae.
Cyanobacteria have a circadian clock that synchronises metabolic processes and allow for the fixation of N2.
Keywords: circadian rhythm; cyanobacteria; heterocyst; nitrogenase; nitrogen fixation
KEY CONCEPTS
Cyanobacteria may fix the ubiquitously available CO2 and N2, and therefore cover the demand of the two most important elements.
The fixation of N2 comes at a high metabolic energy cost, but cyanobacteria are phototrophic organisms that use sunlight to cover their energy demand.
Nitrogenase, the enzyme complex responsible for the fixation of N2, is sensitive to oxygen and requires a near‐to‐anoxic environment.
Cyanobacteria are phototrophic organisms evolving oxygen and they developed various strategies to combine this with N2 fixation.
In order to fix N2, cyanobacteria separate the incompatible processes of oxygenic photosynthesis and N2 fixation spatially (in different cells) or temporally (during the night), or a combination of both.
N2 fixation in the ocean is restricted to the (sub)tropics and carried out by free‐living nonheterocystous filamentous and unicellular cyanobacteria and by symbiotic cyanobacteria living with microalgae.
Heterocystous cyanobacteria are found in freshwater, brackish water, terrestrial environments and symbiotic in plants and algae.
Cyanobacteria have a circadian clock that synchronises metabolic processes and allow for the fixation of N2.
Keywords: circadian rhythm; cyanobacteria; heterocyst; nitrogenase; nitrogen fixation
poojita3:
yeah
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