Bacillus thuringiensis (shortened in LT ) is a bacillus positive Gram, Aérobie and sporulé. One finds it in practically all the grounds, water, the air and the foliage of the plants. It belongs to a group of six bacilli, gathered under the term “groups Bacillus cereus ”: B. anthracis (responsible for the Disease of coal), B. cereus , B. mycoides , B. pseudomycoides , B. weihenstephanensis and B. thuringiensis .

Bacillus thuringiensis was insulated in 1901 by the Japanese bacteriologist S. Ishiwata starting from worms with silk which it can infect and kill.
La the first description scientific must with German E. Berliner in 1911.

Description

At the vegetative state, Bacillus thuringiensis with the shape of a stick of 5 µm length on 1µm broad, and is equipped with Flagelle S.
Il is distinguished from the other bacilli from the cereus group by its capacity to synthesize and excrêter mortally toxic crystals for unquestionable insects. These crystals mineral, but are not formed of the association of several Protéine S which, ensemblent one an insecticidal property on the lépidoptères, the dipterous coleopters and/or the .
Elles acts by destroying the cells of the average intestine of the Larve of insect reached by these toxins, which leads to dead of the insect, which can then be consumed by the bacillus.
On knows currently more than 14 Gène S coding these proteins.

Use

The entomotoxic virtues of Bacillus thuringiensis were at the origin of an agricultural, forestry and commercial interest as of the years 1930, but much more shown at the end of the XXème century, in particular with the development of the genetic Engineering and the Brevetage of alive the.

The first applications of Bacillus thuringiensis in the environment go back to 1933.
Il was used as of the Années 1950 in the Forêt S, the fields and the Vignoble S. < Br > Until the medium of the Années 1970, its principal application was the fight against the lépidoptères défoliateurs in the forests and certain parasitic butterflies of the field crops, of corn in particular.
En 1976, the discovery of the sérotypes israelensis ( Bti ) and tenebrionis allowed the opening of new markets, thanks to an action Larvicide on the Moustique S, the Simulie S and the coleopters.

Advantages/disadvantages:

  • the toxins known as LT are Protéine crystalline very sensitive to the ultraviolet rays which degrades them quickly. This product, when it is used in pulverization thus has the advantage of having a weak remanence on the sheets (less in the ground). This product when it is of natural origin, is authorized in Agriculture bio, in the form of a powder. It is degraded quickly with the sun.

  • the industry of the Biotechnologie S.A. produces transgenic Plantes known as " Bt" , i.e. modified by addition of one or more of genes coding insecticidal toxin (Cry1Ab) of Bacillus thuringiensis .
    Elles produces some in their air fabrics (sheets and stem), in their Pollen, but also in the sphere racinaire (Rhizosphère), from where LT could accumulate longer in the ground.

  • Risks related to the persistence of transgene in the environment? the bacteria are under certain conditions likely to integrate genes of other bacteria. The genes cry1Ab coding the production of proteins (“ delta endotoxine ”) in North-American corn come from B. thurigiensis kurstaki (Btk), very pathogenic bacterium for the butterflies. A study evaluated the frequency and the persistence of the gene cry1Ab of corn LT or the bacillus in the aquatic environments, or near fields where corn LT was cultivated.
    L' study was preceded by a validation of the methodology of preparation of the samples and extraction of the DNA (by PCR) in various matrices (water, ground, sediment.). Surface water and sediments artificially enriched with a known quantity by DNA genomic coming from bacilli or corn LT were then studied in vitro, to evaluate the persistence of the gene cry1Ab. Lastly, of the ground, of the sediments, water and other samples were collected before sowings, then 15 days after the release of the corn pollen, after mechanical harvest and during the ploughing (hiding of the roots) to measure the presence of genes cry1Ab.
    there the gene cry1Ab was persistent lasting on average 21 days in surface water and almost twice longer (41 days) in the sediments. In the argilo-sandy sediments, the gene was still present after 40 days. The study as showed as the genes cry1Ab genes coming from corn transgenic or of natural source are more abundant in the sediments than in surface water. The transgene cry1Ab is transported by the current. The transgene was detected in the rivers Richelieu and the St. Lawrence until (82 km downstream from the zone of culture) suggesting multiple contributions of this gene, or which it is transferred onto long distances before being degraded.
    Le transgene cry1Ab resulting from corn LT tent to decrease as one séloigne of the corn LT cultures, and it is all the more present in the sediments that it is it in surface water (significant Correlation: R = 0,83; P = 0,04). The study thus concluded that the DNA of corn LT and LT persists in the aquatic environments, and that it is present in the rivers draining the agricultural zones and downstream.

  • Persistence of the toxin LT , with risk of impact on the ecosystems?
    Certains enquiring, whose in France the ecotoxicologist Jean-François Narbonne, have with the beginning of the year 2000 alerted on the fact that this LT, while accumulating can end up posing problem: toxicity of the contaminated ground, accumulation in the sediments poison in the River S and Estuaire S. One initially found some in the Fleuve the St. Lawrence in Canada, downstream from the zones of field crop, then Todd Royer, joint author of a recent American study (2007) reinforces and relays this concern in the USA; The analyzes made on 12 sites of the Indiana (the USA) indeed showed that the rates of LT become indeed alarming in the rivers, at the point to affect some Invertébré S watery judged Bioindicateur S of the quality of the watery ecosystems (ex: large phryganea), whose growth is affected by this poison, which kills the phryganea with strong amount. This study, which related to 12 sites chosen in the State of Indiana, allots the origin of this transgenic LT to corn cultivated in the basins slopes of these rivers. They release there from toxins BT in the environment of the catchment area, from where they are brought to the ditches and rivers by the streaming. The study evokes in particular for the first time the role of pollens and waste or corn residues like considerable source of toxins. The latter can accumulate, to degrade themselves and be transported by water to the bottom of the basins slopes. The pollen of corn is enough heavy not to be transported far by the wind (except spring storm), but this pollen of form very round and deprived of spicules is easily carried by the streaming and can then concentrate in certain points (puddle pools, ruts, ditches, sediments of the rivers). The weight of pollen emitted annually per hectare is weak, the number of pollen is very high and the emissions are done massively in a few days or weeks, at the end of spring and at the beginning of the summer with one important moment for many species (reproduction/laying or growth of alevins). Many studies related to the dispersion of viable pollens, but one has little information on their becoming in the environment then.
    Les authors notes that the North-American corn is more and more GMO (almost exclusively), and its surfaces still increased in the plains of the Midwest to produce Agrocarburant S. This corn is precisely often planted near rivers and rivers or of zone irriguables, because it is a particularly consuming water plant.
    Des watery tests of nourrissage of insects with LT, facts at the time of this study showed that with low dose LT inhibited their growth, and that with more raised amount, it increased death rates.

  • Thus contrary to the assertions of the EPA in 1996 at the time of the authorization of first American corn GMO, LT could have collateral impacts on species not-targets. The first test had been made with Daphnie S which are fresh water shellfish and which do not seem affected by LT.

  • Lastly, the risk always exists of appearance of resistances on behalf of insects or other invertebrates which would be constantly exposed there.

See too

Sources

  • “group bacillus cereus”
  • Analysis of the environmental incidences of microbial insecticide '' Bacillus thuringiensis ''
  • Full version in pdf of the article on the environmental incidences of '' Bacillus thuringiensis ''
  • '' Bacillus thuringiensis '' and the transgénèse, on the site of the INRA

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