Cyanobacterial ecology

Cyanobacteria are very self-sufficient. They can tolerate extremely low oxygen concentrations and some can live anaerobically. They are, with certain other bacteria, the only organisms that can fix their own nitrogen, either with the aid of heterocyst cells in aerobic conditions, or without in anaerobic conditions.

Cyanobacteria also have a wide resistance to high and low temperatures, ranging from polar climates to hot thermal springs. They are also very resistant to ultraviolet light. Their lack of cell vacuoles gives them great resistance to desiccation and plasmolysis, hence their presence in arid deserts, glacial regions, hypersaline lagoons and freshwater lakes.

Important limitations appear to be pH and light. They prefer neutral and alkaline environments and never more acid than pH 4.0 The blue-green photo-synthetic pigment phycocyanin is sensitive to blue light and can work under very low light concentrations, so that cyanobacteria can be found living some 300 mm below the soil surface on land and at depths of 1000 m or more in the oceans.

Where nutrient levels are high enough, certain coccoid and filamentous types thrive as very small picoplankton in the water column. Buoyancy is achieved either by the development of pseudovacuoles or by adherence to gas bubbles. Some filamentous forms float in bundles of up to 25 trichomes, forming mats at the surface of the ocean that can extend for many kilometres. In recent years, spring and summer blooms of planktonic cyanobacteria in polluted rivers and lakes have caused poisoning of fish stocks and humans and brought about temporary bottom-water anoxia.

Polluted Cyanobacteria

Fig. 8.4 (a)-(h) Order Nostocales. (a) Recent Oscillatoria. (b) Precambrian Oscillatoria-like filament. (c) Recent Wollea. (d) Precambrian Gunflintia. (e) Precambrian Nostoc-like filament. (f) Recent Rivularia. (g) Precambrian Rivularia-like filament. (h) Recent Scytonema. (i) Order Stigonematales: Devonian, Kidstonella. Scale bar = 10 |m. ((b), (e) and (g) based on Schopf 1972; (d) based on Cloud 1976; (c), (f) and (h) redrawn from Fogg et al. 1973; (i) based on Croft & George 1959.)

Fig. 8.4 (a)-(h) Order Nostocales. (a) Recent Oscillatoria. (b) Precambrian Oscillatoria-like filament. (c) Recent Wollea. (d) Precambrian Gunflintia. (e) Precambrian Nostoc-like filament. (f) Recent Rivularia. (g) Precambrian Rivularia-like filament. (h) Recent Scytonema. (i) Order Stigonematales: Devonian, Kidstonella. Scale bar = 10 |m. ((b), (e) and (g) based on Schopf 1972; (d) based on Cloud 1976; (c), (f) and (h) redrawn from Fogg et al. 1973; (i) based on Croft & George 1959.)

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Responses

  • Ursula
    Why are cyanobacteria so self sufficient?
    8 years ago

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