Bacillus thuringiensis (Bt) è un batterio Gram-positivo che vive nel suolo, comunemente usato come pesticida biologico. È conosciuto per la produzione di proteine tossiche per molte specie di insetti, ma non per l'uomo o altri mammiferi.

Il batterio genera spore e proteine cristalline (proteine Cry) durante la sporulazione. Quando vengono ingerite da alcuni insetti, queste proteine Cry si attivano nelle condizioni alcaline dell'apparato digerente dell'insetto, causandone l'interruzione dell'alimentazione e infine la morte.

A cosa serve e dove si usa

Bacillus thuringiensis è utilizzato nell'agricoltura biologica ed è considerato sicuro per l'uomo e per l'ambiente. Viene anche utilizzato nell'ingegneria genetica per creare colture che producono la tossina Bt e sono resistenti ad alcuni parassiti.

Impatto ambientale

Bacillus thuringiensis  è generalmente considerato ecologico. È altamente specifico per alcuni parassiti, quindi è meno probabile che i pesticidi ad ampio spettro danneggino gli organismi non bersaglio. Tuttavia, ci sono preoccupazioni riguardo alla possibilità che i parassiti sviluppino una resistenza al Bt, soprattutto nel contesto delle colture Bt.

Sicurezza

Bacillus thuringiensis  is considered safe for humans, other mammals, birds, and fish. The Bt toxins are activated by alkaline conditions and specific receptors in the gut, both of which are absent in mammals. However, as with any pesticide, it's important to use Bt responsibly and follow all safety guidelines.

Studi

E. Schnepf, N. Crickmore, J. Van Rie, D. Lereclus, J. Baum, J. Feitelson, D. R. Zeigler, D. H. Dean Bacillus thuringiensis and Its Pesticidal Crystal Proteins  DOI: https://doi.org/10.1128/mmbr.62.3.775-806.1998

Abstract. During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism’s pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

Palma L, Muñoz D, Berry C, Murillo J, Caballero P. Bacillus thuringiensis toxins: an overview of their biocidal activity. Toxins (Basel). 2014 Dec 11;6(12):3296-325. doi: 10.3390/toxins6123296.

Abstract. Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides against caterpillars, beetles, and flies, including mosquitoes and blackflies. Bt also synthesizes insecticidal proteins during the vegetative growth phase, which are subsequently secreted into the growth medium. These proteins are commonly known as vegetative insecticidal proteins (Vips) and hold insecticidal activity against lepidopteran, coleopteran and some homopteran pests. A less well characterized secretory protein with no amino acid similarity to Vip proteins has shown insecticidal activity against coleopteran pests and is termed Sip (secreted insecticidal protein). Bin-like and ETX_MTX2-family proteins (Pfam PF03318), which share amino acid similarities with mosquitocidal binary (Bin) and Mtx2 toxins, respectively, from Lysinibacillus sphaericus, are also produced by some Bt strains. In addition, vast numbers of Bt isolates naturally present in the soil and the phylloplane also synthesize crystal proteins whose biological activity is still unknown. In this review, we provide an updated overview of the known active Bt toxins to date and discuss their activities.