Cyanobacteria

Description

The cyanobacteries are autotrophic organizations Procaryote S not presenting neither true core, neither Plaste, nor sexuée reproduction. They have Chlorophylle and others Pigment S, from where them color which can vary much, but which is in theory blue, which explains their name.

With the Electron microscope, one can distinguish two zones differentiated mainly by their color: the Chromoplaste (peripheral zone containing the Thylakoïde S, kinds of crushed bags containing the photosynthetic organoids) and the Centroplasma (central zone ensuring of the functions similar to that of a core, container of the DNA in the forms of needles). The Chloroplasma, in addition to the Photosynthesis, provides two other functions: the breathing and the fixing of nitrogen at certain species. The cyanobacteries are deprived of nuclear Membrane, of Mitochondrie S, Réticulum, Chromosome S and of Flagelle.

Certain cyanobacteries are also active the night or in the absence of light, being transformed to some extent into chimio-heterotrophic bacteria (by oxidizing sugars). Some also survive in anaérobiose (ex: Oscillatoria limnetica ) while photosynthétisant starting from the Sulfide of hydrogen instead of water.

The cyanobacteries which live in coherent colonies (in Trichome S forming of films, cluster or filaments) fix nitrogen of the air via specialized cells known as Hétérocyste S which function independently of the other cells, in anaérobiose. When the nitrates or the ammonia miss, part of the cells of these cyanobacteries (approximately 10%) thicken their walls, excrêtent their pigments and synthesize an enzyme (Nitrogénase) which fixes the nitrogen (stored in the form of glutamine which can be used by other cells living they of aerobic).

Mobility

Certain cyanobacteries are mobile (often at the Nostocales) and/or can produce Akinète S (cells resisting dehydration thanks to thickened walls).

Reproduction

It is made by vegetative division and Spore S, either Unicellulaire S (Coccospore S), or in the form of filaments of cyanobacteries (Trichome S = Hormogonie S) what constitutes two principal classes of cyanobacteries: the Coccogonophycidée S (solitary or colonial forms) and hormogonophycidées (filamentous colonial forms).

Ecology of the cyanobacteries

The cyanobacteries are the oldest living beings with the Archéobactérie S, since one finds some already during the Précambrien (the simplest forms), which goes back to 3,8 billion years. These species generated geological formations, the Stromatolithe S. Thanks to the activity of the cyanobacteries, of the carbonated rocks could be formed in abundance by thus trapping the Carbonic gas of the primitive Atmosphère, which could provide us many information as for the composition of the atmosphere, therefore on the living conditions of the time. They are at the origin of the modification of the terrestrial atmosphere with enrichment in Dioxygène, necessary to the development of the life on Earth by allowing the appearance of the protective Couche of ozone, and of the first large Puits of carbon which decreased the Greenhouse effect, whereas the temperature of the Sun increased.

Cyanophycées live almost everywhere, including under extreme conditions, polar ices with sands of the deserts. They survive in the very hot and/or acid lakes of the volcanic craters as in the geysers. They grow so much out of salted fresh water than, in ic form Plancton (alive in the water mass), or in form Benthique (organizations fixed at a Substrat immersed). They develop particularly well in certain mediums polluted by the human activities (Eutrophisation, Dystrophisation). These proliferations (bloom S) form for example water flowers of particular color which appear on a water level in the process of pollution. One attends these efflorescences alguales when water contains Azote and/or Phosphore in excess, consequence for example of a too intensive agriculture or an urbanization purifying his water badly. For this reason, when one detects that a stretch of water is invaded by the cyanobacteries, one should not regard the efflorescence itself pollution, but rather as a natural reaction to a pollution already present.

Toxicity

The efflorescences algales are not without consequence, since certain species release from the endotoxine S (in particular during the rupture or of died of the cells) which can be dangerous for the man and the animals, affecting mainly the Peau and the Muqueuse S (dermatotoxines), the Foie (hépatotoxines) and the nervous system (neurotoxines). The proliferations of surface, by decreasing the penetration of the light in water, also harm other groups of algae and limit the gaseous exchange between the atmosphere and water (moreover they consume the oxygen of water) and can thus lead to a Asphyxie (or Anoxie) of the aquatic animals or medium. However, other species of the normal Phytoplankton, not poisons, are sometimes causes of an exceptional output in Poisson S of certain ponds or marine zones. The toxins or their mechanisms of action are not yet all known (ex for Coelosphaerium kuetzingianum) .

Cyanobacteries and nitrogenizes

These algae play a big role in the Cycle of the nitrogen, while being able to transform atmospheric nitrogen into Ammonium or assimilable Nitrate S by the plants. While dying, they release from the nutritive salts produced by the fixing of nitrogen and thus increase the agricultural output, particularly in rice growings. They sometimes thus are used as “green” Engrais to bring a contribution of directly assimilable Azote by the plants.

They can also live in Symbiose, for example as algaux components of the Lichen S (Gonidie S) associated with a Champignon.
Les therapeutic properties of the mud baths would be due in major part to the cyanobacteries.
Certaines species as the Spiruline ( Arthrospira platensis ) also constitutes a very good food complement.

Relations with the chloroplasts

The Chloroplaste S which one finds at the photosynthetic Eucaryote S, like the Algue S and the plants (i.e. primary education producers) result most probably from endosymbiotic cyanobacteries. This endosymbiotic theory is supported by various structural and genetic similarities. Plastids resulting from a primary endosymbiose which contain Chlorophylle has and B was found among the green algas and the Plante S as of the plastids which contain chlorophyl has and of the phycobiliprotéines among red algas S and Glaucophyte S. These plastids probably had a common origin. Other algae acquired their plastids starting from these forms by endosymbiose or secondary ingestion (for the green line: Euglénophytes and Chlorarachniophytes starting from a green alga, and for the red line: all brown algas in the broadest sense of the term - Hétérokontophytes, Cryptophytes, Dinophycées, Haptophytes, etc - starting from a red alga).

Cyanobacteries out of aquarium

In aquariophilie, the presence of certain cyanobacteries known as “ encrusting algae ” announces a problem to the level of water. These algae often appear after a lack of maintenance or an important and brutal imbalance. The organic matters in decomposition support also their developments. Their mode of reproduction make them almost invincible vis-a-vis the utility of cleaning of the aquarist, and some fragments are enough to reform a thick crust.

Cyanobacteries in the drinking water tanks

The water of tanks supplied with rivers or rain water can be contaminated by toxic cyanobacteries. It seems that this phenomenon is in increase since the years 1970. One will find there for example (northern Hemisphere)

Anabaena flosaquae
Anabaena planctonica
Anabaena solitaria
Anabaena spiroid
Anabaena sp.
Aphanizomenon flosaquae
Coelosphaerium kuetzingianum
Coelosphaerium naegilianum
Gomphosphaeria aponica
Gomphosphaeria lacustris
Microcystis flosaquae
Microcystis sp.
Oscillatoria aghardii

Causes

On the level of water, the suspectées causes are a content too high of organic matter, in Nitrate S and/or Phosphate S. In an aquarium, lighting can be in question (too much, not enough or inappropriate source). The time of lighting should be ranging between 10 and 12 hours per day. External contaminations by introduction of algae can be in question. By precaution, on the contaminated external sites, nautical activities others that bathe or diving is sometimes authorized provided that a washing/careful rinsing of the material follows the activity, not to contaminate other sites.

With the Quebec, in 3 years of 2001 to 2004, out of 6 pumping stations of drinking water, Anabaena flosaquae , Coelosphaerium kuetzingianum were rather frequently detected, as well as ten of other stocks. The greatest number of potentially toxic species was on the sites of Plessisville, Saint-Hyacinthe and Farnham. In a third of the cases approximately, the presence of one or more species of cyanophycée was associated with a detectable concentration of cyanotoxine. Knowing that these species are characterized by planktonique blooms, without measurement regular and very brought closer, one is never certain to measure the maximum . The river Bécancour, the river Yamaska and the Bay Missisquoi which are used as drinking water tank, contained some atrates " often higher than the threshold of alarm proposed by Bartram and Al (1999) for the drinkable water provision, is 2.000 cellules/ml ". The cyanotoxines however only seldom were detected with the tap, or low values thanks to a good water treatment; stations of potabilisation succeeding in eliminating the cyanobacteries without making burst their cells, i.e. releasing the intracellular cyanotoxines in water or by filtering them on the activated charcoal.

Undesirable out of aquarium

These algae readily proliferating and sometimes producing of toxins are undesirable out of aquarium where they can form a sticky carpet on the plants, preventing their normal chlorophyllian activity, weakening them and killing them, their death contributing to pollute water.
Le sand covered by a carpet with algae any more is not drained and is oxygenated, becoming unsuitable with any aerobic microbial life.
Les cyanobacteries fixing nitrogen, they compete with the " good bactéries" present in the aquarium (Nitrobacter and Nitrosomonas), which unbalances the ecosystem in place in the long run.
Solutions: Agir on one of the factors often does not produce any result. The Nitrate S, even not very present, can be compensated by the fixing of nitrogen. It is recommended to clean the aquarium and its filter before important water changes, while taking care of an adapted lighting, and by avoiding the contribution of CO₂ temporarily. One one week period in the total black, combined with a good cleaning of the vat and an oxygenation of the aquarium could sometimes suffir with the éradiquer. Into last recourse, antibiotics (érythromycine at a rate of 200 Mg for 100 liters) are effective, but will kill also the good bacteria (ecological imbalance), while being likely to create resistant stocks. The fish can be transferred in another aquarium time from the treatment for to in particular avoiding an ammonia peak or nitrites them, before filtering on activated carbon then to resow the aquarium in good bacteria, once the finished treatment.

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