Transgenic organisms expressing genes fromBacillus thuringiensisto combat insect pests

Abstract

Bti is highly efficient and specific against mosquito and black fly larvae. 3 Most importantly, no resistance has been observed in nature after about 30 years of extensive use worldwide. 4 Different activities and modes of action of its four major toxins form a lethal combination against larvae of all mosquito species tested. 5 Resistance is not selected due to synergy among Bti components, mostly the lowtoxic, non-specific Cyt1Aa. High synergy levels affected by Cyt1Aa were observed by Crickmore 6 and Wirth, 7 the latter also demonstrated that Cyt1Aa prevented selection of resistant mosquitoes. 8The question raised was whether a combination of antiLepidopteran toxins with Cyt1Aa imitates this rare advantage of Bti. To partially answer this question, two genes were cloned for expression in Escherichia coli, cry1Ac (from Bt ssp. kurstaki) and cry1Ca (from Bt ssp. aizawai), with and without cyt1Aa, and tested against three pests, Helicoverpa armigera, Pectinophora gossypiella and Spodoptera littoralis.9 Co-expression of all three genes, and with p20 encoding an accessory protein (for reasons beyond Various subspecies (ssp.) of Bacillus thuringiensis (Bt) are considered the best agents known so far to control insects, being highly specific and safe, easily mass produced and with long shelf life.1 The para-crystalline body that is produced during sporulation in the exosporium includes polypeptides named d-endotoxins, each killing a specific set of insects. The different entomopathogenic toxins of various Bt ssp. can be manipulated genetically in an educated way to construct more efficient transgenic bacteria or plants that express combinations of toxin genes to control pests.2 Joint research projects in our respective laboratories during the last decade demonstrate what can be done by implementing certain ideas using molecular biology with Bt ssp. israelensis (Bti) as a model system. Here, we describe our progress achieved with Gram-negative bacterial species, including cyanobacteria, and some preliminary experiments to form transgenic plants, mainly to control mosquitoes (Diptera), but also a particular Lepidopteran and Coleopteran pest species. In addition, a system is described by which environment-damaging genes can be removed from the recombinants thus alleviating procedures for obtaining permits to release them in nature.

Toward mosquito control with a green alga: expression of Cry toxins of Bacillus thuringiensis subsp. israelensis (Bti) in the chloroplast of Chlamydomonas

“…The most effort has been based on modifying cyanobacteria to synthesize the larvacidal proteins of Bti (Angsuthanasombat and Panyim 1989; Stevens et al 1994; Soltes-Rak et al 1995; Zaritsky et al 2010). In the most successful series to date, Zaritsky and colleagues developed a larvicidal Anabaena strain with chromosomally-expressed (ie, not plasmid-born) genes for cry4Aa and cry11Aa that was quite toxic to Aedes and Culex larvae (Wu et al 1997).…”

“…In the most successful series to date, Zaritsky and colleagues developed a larvicidal Anabaena strain with chromosomally-expressed (ie, not plasmid-born) genes for cry4Aa and cry11Aa that was quite toxic to Aedes and Culex larvae (Wu et al 1997). However, the Anabaena strain has not, to our knowledge, been employed for mosquito control, due partly to concerns over the bacterial antibiotic-resistance gene(s) that it contains (Zaritsky et al 2010). It also lacked the cyt1Aa gene needed to prevent the development of resistance, although cyt1Aa gene could be present on a plasmid with these genes in other strains (Khasdan et al 2003).…”

Identification, Cloning and Expression of an Insecticide <b><i>cry8</i></b> Gene from <b><i>Bacillus</i></b><b><i>thuringiensis </i></b>INTA Fr7-4

“…Bacillus thuringiensis is a spore-forming, Gram-positive, ubiquitous bacterium, characterized by the production of proteinaceus parasporal inclusions known as the generation of transgenic plants expressing Cry proteins in their tissues, including corn, cotton, soybean and canola as leading exponents [Zaritsky et al, 2010].…”

Dietary and phylogenetic correlates of digestive trypsin activity in insect pests

“…In addition, higher larval mortality was achieved by applying TMOF with other insecticidal proteins, such as toxins of B. thuringiensis (Borovsky et al., ; Misni et al., ; Saiful et al., ) and nucleopolyhedrovirus chitinase A (Fiandra et al., ). Transgenic plants expressing TMOF have negative effects on lepidopteran (Tortiglione et al., ) and mosquito larvae (Zaritsky et al., ).…”