blue-green algae


blue-green algae
a widely distributed group of predominantly photosynthetic prokaryotic organisms of the subkingdom Cyanophyta, resembling phototrophic bacteria, occurring singly or in colonies in diverse habitats: some species can fix atmospheric nitrogen. Also called cyanobacteria.
[1895-1900]

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also called  cyanobacteria 

      any of a large, heterogeneous group of prokaryotic, principally photosynthetic organisms. Cyanobacteria resemble the eukaryotic algae in many ways, including morphological characteristics and ecological niches, and were at one time treated as algae, hence the common name of blue-green algae. Algae have since been reclassified as protists, and the prokaryotic nature of the blue-green algae has caused them to be classified with bacteria in the prokaryotic kingdom Monera.

      Like all other prokaryotes, cyanobacteria lack a membrane-bound nucleus, mitochondria, Golgi apparatus, chloroplasts, and endoplasmic reticulum. All of the functions carried out in eukaryotes by these membrane-bound organelles are carried out in prokaryotes by the bacterial cell membrane. Some cyanobacteria, especially planktonic forms, have gas vesicles that contribute to their buoyancy. Chemical, genetic, and physiological characteristics are used to further classify the group within the kingdom. Cyanobacteria may be unicellular or filamentous. Many have sheaths to bind other cells or filaments into colonies.

      Cyanobacteria contain only one form of chlorophyll, chlorophyll a, a green pigment. In addition, they contain various yellowish carotenoids, the blue pigment phycobilin, and, in some species, the red pigment phycoerythrin. The combination of phycobilin and chlorophyll produces the characteristic blue-green colour from which these organisms derive their popular name. Because of the other pigments, however, many species are actually green, brown, yellow, black, or red.

      Most cyanobacteria do not grow in the absence of light (i.e., they are obligate phototrophs); however, some can grow in the dark if there is a sufficient supply of glucose to act as a carbon and energy source.

      In addition to being photosynthetic, many species of cyanobacteria can also “fix” atmospheric nitrogen (nitrogen fixation)—that is, they can transform the gaseous nitrogen of the air into compounds that can be used by living cells. Particularly efficient nitrogen fixers are found among the filamentous species that have specialized cells called heterocysts. The heterocysts are thick-walled cell inclusions that are impermeable to oxygen; they provide the anaerobic (oxygen-free) environment necessary for the operation of the nitrogen-fixing enzymes. In Southeast Asia, nitrogen-fixing cyanobacteria often are grown in rice paddies (paddy), thereby eliminating the need to apply nitrogen fertilizers.

      Cyanobacteria range in size from 0.5 to 60 micrometres, which represents the largest prokaryotic organism. They are widely distributed and are extremely common in fresh water, where they occur as members of both the plankton and the benthos. They are also abundantly represented in such habitats as tide pools, coral reefs, and tidal spray zones; a few species also occur in the ocean plankton. On land, cyanobacteria are common in soil down to a depth of 1 m (39 inches) or more; they also grow on moist surfaces of rocks and trees, where they appear in the form of cushions or layers.

      Cyanobacteria flourish in some of the most inhospitable environments known. They can be found in hot springs, in cold lakes underneath 5 m of ice pack, and on the lower surfaces of many rocks in deserts. Cyanobacteria are frequently among the first colonizers of bare rock and soil. Various types of associations take place between cyanobacteria and other organisms. Certain species, for example, grow in a mutualistic relationship with fungi, forming composite organisms known as lichens.

      Cyanobacteria reproduce asexually, either by means of binary or multiple fission in unicellular and colonial forms or by fragmentation and spore formation in filamentous species. Under favourable conditions, cyanobacteria can reproduce at explosive rates, forming dense concentrations called blooms. Cyanobacteria blooms can colour a body of water. For example, many ponds take on an opaque shade of green as a result of overgrowths of cyanobacteria, and blooms of phycoerythrin-rich species cause the occasional red colour of the Red Sea. Cyanobacteria blooms are especially common in waters that have been polluted by nitrogen wastes; in such cases, the overgrowths of cyanobacteria can consume so much of the water's dissolved oxygen that fish and other aquatic organisms perish.

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Universalium. 2010.

Look at other dictionaries:

  • blue-green algae — [blo͞o′grēn′] pl.n. any of a division (Cyanophycota) of photosynthetic monerans, microorganisms that contain a blue pigment which obscures the chlorophyll; cyanobacteria …   English World dictionary

  • blue-green algae — cyanobacterium cyanobacterium pl. cyanobacteria cyanobacteria [from the pigment phycocyanin.] any of a group of photosynthetic autotrophic prokaryotic microorganisms possessing characteristics of both bacteria and plants. When classed as bacteria …   The Collaborative International Dictionary of English

  • blue-green algae — melsvabakterės statusas T sritis ekologija ir aplinkotyra apibrėžtis Vienaląsčiai (rutulio, ritinio, verpstės, pjautuvo formos), kolonijiniai ar daugialąsčiai (siūliški) organizmai (Cyanobacteria) – melsvai žalios bakterijos, paplitusios… …   Ekologijos terminų aiškinamasis žodynas

  • blue-green algae — blue green alga lue green al ga pl. {blue green al gae} [from the color and resemblance to algae.] any of a group of photosynthetic microorganisms possessing characteristics of both bacteria and plants. When classed as bacteria, they are… …   The Collaborative International Dictionary of English

  • blue-green algae — blue′ green al′gae n. pl. mcr any of various groups of prokaryotic microorganisms of the phylum Cyanophyta, containing chlorophyll and a blue pigment Also called cyanobacteria • Etymology: 1895–1900 …   From formal English to slang

  • blue-green algae — /ˌblu grin ˈældʒi/ (say .blooh green aljee) plural noun a poisonous blue green growth resembling algae occurring in stagnant fresh water in hot weather. See cyanobacteria …   Australian English dictionary

  • blue-green algae — noun predominantly photosynthetic prokaryotic organisms containing a blue pigment in addition to chlorophyll; occur singly or in colonies in diverse habitats; important as phytoplankton (Freq. 1) • Syn: ↑cyanobacteria • Derivationally related… …   Useful english dictionary

  • blue-green algae — Group of prokaryotes that should now be referred to as Cyanobacteria …   Dictionary of molecular biology

  • blue-green algae — Cyanobacteria …   Medical dictionary

  • blue-green algae — plural noun another term for cyanobacteria …   English new terms dictionary


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