Cyanobacteria

the blue-green bacteria (formerly called blue-green algae), a subgroup of the kingdom Procaryotae, unicellular or filamentous phototrophic organisms that use water as an electron donor and produce oxygen in the presence of light. They are the only organisms that fix both carbon dioxide (in the presence of light) and nitrogen. Most species are photosynthetic and many are strong nitrogen fixers. Several species are common causes of water pollution and are often used as indicators of eutrophication of lakes and streams.

Cy·a·no·bac·te·ri·a

(sī'ă-nō-bak-tēr'ē-ă),

A division of the kingdom Prokaryotae consisting of unicellular or filamentous bacteria that are either nonmotile or possess a gliding motility, reproduce by binary fission, and perform photosynthesis with the production of oxygen. These blue-green bacteria were formerly referred to as blue-green algae.

Synonym(s): Cyanophyceae

Farlex Partner Medical Dictionary © Farlex 2012

Cy·a·no·bac·te·ri·a

(sī'ă-nō-bak-tēr'ē-ă)

Medical Dictionary for the Health Professions and Nursing © Farlex 2012

cyanobacteria (formerly blue-green algae)

a PHYLUM within the DOMAIN BACTERIA (see CLASSIFICATION). Cyanobacteria are a group of photosynthetic PROKARYOTES capable of OXYGENIC PHOTOSYNTHESIS. Some are also capable of ANOXYGENIC PHOTOSYNTHESIS. They were formerly called blue-green algae mainly because of the colour of many species, caused by a blue pigment called phycocyanin. They may also contain a red pigment called phycoerythrin. All members contain chlorophyll a. However, Prochloron additionally contains chlorophyll b (see CHLOROPHYLL). The cyanobacteria were possibly the first ORGANISMS on the earth to produce OXYGEN by photosynthesis. There is fossil evidence for their occurrence 3.5 x 109 years ago. The CELL WALL is analogous to that of Gram-negative BACTERIA (see GRAM'S STAIN and the LIGHT REACTIONS of photosynthesis occur on the THYLAKOID MEMBRANE system, within the cell. Other structures in the cell include carboxysomes, polyphosphate bodies as a PHOSPHATE reserve, and gas VACUOLES for buoyancy Some cyanobacteria are UNICELLULAR, others are filamentous (see FILAMENT (2)). They reproduce by fission or fragmentation. A number of species shows CELLULAR DIFFERENTIATION, with the formation of, for example, AKINETES, and specialized cells for NITROGEN FIXATION, called heterocysts. Cyanobacteria are widespread, being found in both terrestrial and aquatic environments that are illuminated. Some live in very inhospitable environments such as hot springs, where the temperature is in excess of 85 °C. They are responsible for much of the photosynthetic oxygen evolution in oceans and contribute to productivity through CARBON DIOXIDE fixation (see DARK REACTIONS) and NITROGEN FIXATION. Sometimes they accumulate in large numbers as BLOOMS on the surface of lakes, reservoirs and so on. These blooms may produce TOXINS.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

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References in periodicals archive

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According to researchers, Cyanothece, the type of Cyanobacteria under study is able to fix nitrogen because of something it has in common with people ndash the circadian rhythm or biological clock.They photosynthesise during the day, converting sunlight to the chemical energy they use as fuel, and fix nitrogen at night after removing most of the oxygen created during photosynthesis through respiration.

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