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Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. [1] Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts. [2]
Trichodesmium erythraeum is a marine cyanobacteria species characterized by its prolific diazotrophic capabilities. [1] They play a dominant role in the ocean ecosystem, supplying a steady and significant source of new, biologically available nitrogen and cycling phosphorus. [2]
The colonial marine cyanobacterium Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. [52] Marine surface lichens and non-photosynthetic bacteria belonging in Proteobacteria and Planctomycetes fixate significant atmospheric nitrogen. [ 53 ]
[39] [118] [46] In contrast to free-living marine cyanobacteria, some cyanobionts are known to be responsible for nitrogen fixation rather than carbon fixation in the host. [119] [120] However, the physiological functions of most cyanobionts remain unknown.
As a result, marine N 2-fixing microorganisms other than Trichodesimum were found by sequencing PCR-amplified fragments of the gene nitrogenase (nifH) .Nitrogenase is the enzyme that catalyzes nitrogen fixation, and studies have shown that nifH is widely distributed throughout the different parts of the ocean. [10]
Some cyanobacteria, including the highly abundant marine taxa Prochlorococcus and Synechococcus do not fix nitrogen, [5] whilst other marine cyanobacteria, such as Trichodesmium and Cyanothece, are major contributors to oceanic nitrogen fixation.
Nitrogen enters the ocean through precipitation, runoff, or as N 2 from the atmosphere. Nitrogen cannot be utilized by phytoplankton as N 2 so it must undergo nitrogen fixation which is performed predominantly by cyanobacteria. [82] Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 ...
2 so it must undergo nitrogen fixation which is performed predominately by cyanobacteria. [41] Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 years. [42] Phytoplankton need nitrogen in biologically available forms for the initial synthesis of organic matter.