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In general, photosynthesis in cyanobacteria uses water as an electron donor and produces oxygen as a byproduct, though some may also use hydrogen sulfide [80] a process which occurs among other photosynthetic bacteria such as the purple sulfur bacteria. Carbon dioxide is reduced to form carbohydrates via the Calvin cycle. [81]
Abundant growth of cyanobacteria in freshwater, estuarine, and coastal ecosystems due to increased anthropogenic eutrophication and global climate change has created serious concern toward harmful bloom formation and surface water contamination. [8] Cyanobacteria are considered the most primitive groups of photosynthetic prokaryotes [9] and ...
Some types of cyanobacteria are endosymbiont and cyanobacteria have been found to possess genes that enable them to undergo nitrogen fixation. [165] Organisms typically establish a symbiotic relationship due to their limited availability of resources in their habitat or due to a limitation of their food source.
Originally, biologists thought cyanobacteria was algae, and referred to it as "blue-green algae". The more recent view is that cyanobacteria are bacteria, and hence are not even in the same Kingdom as algae. Most authorities exclude all prokaryotes, and hence cyanobacteria from the definition of algae. [26] [27]
Here, the water is chilled by Arctic temperatures. It also gets saltier because when sea ice forms, the salt does not freeze and is left behind in the surrounding water. The cold water is now more dense, due to the added salts, and sinks toward the ocean bottom. Surface water moves in to replace the sinking water, thus creating a current.
Most cyanobacteria produce toxins, of which microcystin is only one group. When a cyanobacterium dies, its cell wall degrades while the toxins are released in the water. Microcystins are extremely stable in water and withstand chemical breakdown such as hydrolysis or oxidation. The half-life of this toxin is 3 weeks at pH 1 and 40 °C.
Because of this, cyanobacteria are known to be important in the nitrogen and phosphate fixing cycle in oligotrophic waters. [26] Cyanobacteria can fix nitrogen by accessing atmospheric nitrogen (N 2) that has been dissolved into water and transforming it into nitrogen accessible to other organisms. [26]
Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission , fragmentation , or budding ; unlike bacteria and eukaryotes, no known species forms spores .