The Bacillus thuringiensis cyt Genes for Hemolytic Endotoxins Constitute a Gene Family

Abstract

In the same way that cry genes, coding for larvicidal delta endotoxins, constitute a large and diverse gene family, the cyt genes for hemolytic toxins seem to compose another set of highly related genes in Bacillus thuringiensis. Although the occurrence of Cyt hemolytic factors in B. thuringiensis has been typically associated with mosquitocidal strains, we have recently shown that cyt genes are also present in strains with different pathotypes; this is the case for the morrisoni subspecies, which includes strains biologically active against dipteran, lepidopteran, and coleopteran larvae. In addition, while one Cyt type of protein has been described in all of the mosquitocidal strains studied so far, the present study confirms that at least two Cyt toxins coexist in the more toxic antidipteran strains, such as B. thuringiensis subsp. israelensis and subsp. morrisoni PG14, and that this could also be the case for many others. In fact, PCR screening and Western blot analysis of 50 B. thuringiensis strains revealed that cyt2-related genes are present in all strains with known antidipteran activity, as well as in some others with different or unknown host ranges. Partial DNA sequences for several of these genes were determined, and protein sequence alignments revealed a high degree of conservation of the structural domains. These findings point to an important biological role for Cyt toxins in the final in vivo toxic activity of many B. thuringiensis strains.

Phenotypic characterization of an indigenous Bacillus thuringiensis strain (B.T. LDC 501) expressing cancer cell killing protein

“…This action differs from broad cytolytic Cyt proteins that kill both normal and cancer cells (Thomas & Ellar, 1983). This is correlated with the earlier studies that denoted the association of cyt genes with haemolysis and mosquitocidal action (Guerchicoff et al, 2001). …”

Amino acids at N- and C-termini are required for the efficient production and folding of a cytolytic γ-endotoxin from Bacillus thuringiensis

“…The toxins in this group also evidence cytolytic activity to a broad range of cells, including erythrocytes, in vitro (3)(4)(5)(6). The amino acid sequences of all Cyt toxins show a high degree of homology with each other (7), and therefore all of them should evidence similar 3D structures. On the basis of the X-ray crystallographic structure of Cyt2Aa1 (8), all Cyt toxins should be single domain proteins with alpha-beta architectures, comprised of six helices and seven beta sheets, in which the two outer-layers of the alpha helix hairpins are wrapped around a mixed beta sheet (8).…”

Compaction of the Escherichia coli nucleoid caused by Cyt1Aa

“…Seven cytolytic, mosquitocidal-specific toxins are currently known (Earp & Ellar, 1987;Drobniewski & Ellar, 1989;Yu et al, 1991;Koni & Ellar, 1993;Cheong & Gill, 1997;Guerchicoff et al, 1997;Thiery et al, 1997). Using heavyatom isomorphous replacement, the crystal structure of Cyt2Aa from B. thuringiensis subsp.…”

“…The broad cytolytic activity of Cyt1Aa has been attributed to its hydrophobicity and ability to bind zwitterionic phospholipids (Thomas & Ellar, 1983a, b). Cyt1Aa is inserted into the membrane to create cation-selective single channels of 1-2 nm in diameter, leading to colloid-osmotic lysis (Knowles & Ellar, 1987;Knowles et al, 1989), and induces leakage of low-molecular-mass substances from lipid vesicles (Drobniewski & Ellar, 1988.Seven cytolytic, mosquitocidal-specific toxins are currently known (Earp & Ellar, 1987;Drobniewski & Ellar, 1989;Yu et al, 1991;Koni & Ellar, 1993;Cheong & Gill, 1997;Guerchicoff et al, 1997;Thiery et al, 1997). Using heavyatom isomorphous replacement, the crystal structure of Cyt2Aa from B. thuringiensis subsp.…”