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| Cyanobacteria
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Anabaena sperica ( Nostocales ) | ||||
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Cyanobacteria are a phylum of aquatic bacteria that obtain their energy through photosynthesis. They are often referred to as blue-green algae, even though it is now known that they are not related to any of the other algal groups, which are all eukaryotes. Nonetheless, the description is still sometimes used to reflect their appearance and ecological role. Fossil traces of cyanobacteria are claimed to have been found from around 3.8 billion years ago, but recent evidence has sparked controversy over this assertion. See: Stromatolite
Cyanobacteria include unicellular, colonial and filamentous forms. Some filaments form differentiated cells that are specialized for nitrogen fixation, called heterocysts, and resting cells called akinetes. Each individual cell typically has a thick, gelatinous cell wall, which has a gram-negative stain. They lack flagella, but may move about by gliding along surfaces. Most are found in freshwater, but some are marine or occur in damp soil. A few are endosymbionts in lichens or of various protistRhodophyta (red algae) Heterokontophyta (heterokonts) Cryptophyta (cryptomonads) Pyrrhophyta (dinoflagellates) Apicomplexa Ciliophora (ciliates) Euglenozoa Metamonada Foraminifera Cercozoa Amoebozoa Choanozoa Many others; classification varies The Kingdoms, and provide energy for their host.
Photosynthesis in cyanobacteria generally uses water as an electron donor and produces oxygenOxygen is the chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O, often called free oxygen on Earth is thermodynamically un as a by-product, though some may also use hydrogen sulfideProperties General Name Hydrogen sulfide Chemical formula H S Appearance Colourless gas Physical Formula weight 34. 1 amu Melting point 187 K (-86 °C) Boiling point 213 K (-60 °C) Solubility 0. 33 g in 100g water Thermochemistry ΔH0 -20. 5 kJ/ mol & as occurs among other photosynthetic bacteria. Carbon dioxideCarbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. One of the best known of chemical compounds, it is frequently called by its formula: :CO (pronunciation: "see oh two") Carbon dioxide results from the combustion of organic is reduced to form carbohydrates via the Calvin cycleThe Calvin cycle (also known as Calvin-Benson cycle is a series of biochemical reactions taking place in the chloroplasts of photosynthetic organisms. It was discovered by Melvin Calvin and Andy Benson at the University of California, Berkeley. During pho. In most forms the photosynthetic machinery is embedded into folds of the cell membrane, called thylakoidA thylakoid is part of an internal membrane system of chloroplasts folded repeatedly into a stack of disks called grana. Thylakoids have light absorbing pigments ( chlorophylls) and enzymes required to form ATP, NADPH, or both in photosynthesis. The stacks. The large amounts of oxygen in the atmosphere are considered to have been first created by the activities of ancient cyanobacteria.There are two main sorts of pigmentation. Most cyanobacteria contain chlorophyll a, together with various proteins called phycobilins, which give the cells a typical blue-green to grayish-brown colour. A few genera, however, lack phycobilins and have chlorophyll b as well as a, giving them a bright green colour. These were originally grouped together as the prochlorophytes or chloroxybacteria, but appear to have developed in several different lines of cyanobacteria.
Chloroplasts found in eukaryotes (algae and higher plants) most likely represent reduced endosymbiotic cyanobacteria. This endosymbiotic theory is supported by various structural and genetic similarities. Primary chloroplasts are found among the green plants, where they contain chlorophyll b, and among the red algae and glaucophytes, where they contain phycobilins. It now appears that these chloroplasts probably had a single origin. Other algae likely took their chloroplasts from these forms by secondary endosymbiosis or ingestion.See hypolith for an example of cyanobacteria living in extreme conditions.
The cyanobacteria are traditionally classified by morphology into five sections, which may be simply referred to by the numerals I-V. The first three - Chroococcales , Pleurocapsales , and Oscillatoriales - are not supported by phylogenetic studies. However, the latter two - Nostocales and Stigonematales - are monophyletic, and make up the heterocystous cyanobacteria.
Certain cyanobacteria secrete cyanotoxins like Anatoxin-a , Anatoxin-as , Aplysiatoxin , Cylindrospermopsin , Domoic acid, Microcystin LR , Nodularin R , or Saxitoxin . Sometimes a mass- reproduction of cyanobacteria results in algal blooms.
Bacteria