Genetic and genomic contexts of toxin genes

This chapter focuses primarily on the genomic distribution (plasmid vs chromosome) and the genetic environments of the different toxin genes found in entomopathogenic bacteria, mainly in Bacillus thuringiensis and Bacillus sphaericus. A special attention is brought to their association with mobile genetic elements (Insertion Sequences, Transposons and conjugative plasmids) and their possible clustering to other, more generic, virulence factors, in the scope of genome variability and plasticity through gene transfer and rearrangements

Vector-active toxins: structure and diversity

Bacteria active against Dipteran larvae — mosquitoes and blackflies — include a wide variety of Bacillus thuringiensis and Bacillus sphaericus strains, as well as isolates of Brevibacillus laterosporus and Clostridium bifermentans. All display different spectra and levels of activity correlated with the nature of the toxins produced during the sporulation process. This paper presents an overview of all mosquitocidal strains reported to date and describes the numerous toxins — including both Cry and Cyt proteins, and others — in terms of primary structure and activity against mosquito larvae

Characterization of Cyt2Bc Toxin from Bacillus thuringiensis subsp. medellin

We cloned and sequenced a new cytolysin gene from Bacillus thuringiensis subsp. medellin. Three IS240-like insertion sequence elements and the previously cloned cyt1Ab and p21 genes were found in the vicinity of the cytolysin gene. The cytolysin gene encodes a protein 29.7 kDa in size that is 91.5% identical to Cyt2Ba from Bacillus thuringiensis subsp. israelensis and has been designated Cyt2Bc. Inclusions containing Cyt2Bc were purified from the crystal-negative strain SPL407 of B. thuringiensis. Cyt2Bc reacted weakly with antibodies directed against Cyt2Ba and was not recognized by an antiserum directed against the reference cytolysin Cyt1Aa. Cyt2Bc was hemolytic only upon activation with trypsin and had only one-third to one-fifth of the activity of Cyt2Ba, depending on the activation time. Cyt2Bc was also mosquitocidal against Aedes aegypti, Anopheles stephensi, and Culex quinquefasciatus, including strains resistant to the Bacillus sphaericus binary toxin. Its toxicity was half of that of Cyt2Ba on all mosquito species except resistant C. quinquefasciatus