Parasporins from a Caribbean Island: Evidence for a Globally Dispersed Bacillus thuringiensis Strain

Abstract

Parasporins represent a new functional class of Cry (crystal protein) toxins produced by the bacterium Bacillus thuringiensis (Bt). Unlike Cry toxins that demonstrate activity mainly against some insect cells, parasporins are characterized as being non-hemolytic, yet capable of preferentially killing some human cancer cells. Globally, six different parasporin types, PS1-PS6, based on protein sequence homology, have been identified in only four countries (Japan, Vietnam, India, and Canada). Herein we report the results of a screening study of 160 Bt isolates collected from the Caribbean island of Trinidad. One isolate (strain 64-1-94) was shown to kill human cancer cells and to contain one ps6 and two ps1 parasporin genes. The two ps1 genes were located approximately 6 kb apart from each other, sharing a similar spatial arrangement, and high sequence homology, with two plasmid-located ps1 genes, ps1Aa6 and ps1Ad1, recently isolated from a Japanese strain. Evidence is also presented that a parasporin gene reported previously for a Canadian strain, ps1Aa2, is most likely derived from a recombination event between these same two genes found in the Trinidadian and Japanese strains. Notably, all three strains share a ps6 parasporin gene, presumably located on a separate plasmid. These data suggest that the global population of ps1 genes may be have originated from a single pair of parasporin genes. Given the large geographical distance between the collection sites, which are located on both continental land masses and islands at sea, ps1 genes are able to retain a remarkable level of homology not easily explained.

Recurrent Horizontal Transfer of Bacterial Toxin Genes to Eukaryotes

“…The fact that several aerolysin homologues from bacteria were found on phages and plasmids provides further support for an HGT scenario, especially within prokaryotes, and it is possible that these vectors also contribute to the mobilization of aerolysin genes between diverse lineages (Nakayama et al 1999; Miyamoto et al 2008; Gonzalez et al 2011). If we consider only clusters with reliable phylogeny, then at least six HGT events between kingdoms of life have occurred in the evolution of the aerolysin family.…”

Parasporin-2 from a New Bacillus thuringiensis 4R2 Strain Induces Caspases Activation and Apoptosis in Human Cancer Cells

“…Thuringiensis strains. As shown in a previous study, cry genes coding for the same parasporin protein can be geographically dispersed [ 36 ]. This supports the fact that the B .…”

Toxicity of Parasporin-4 and Health Effects of Pro-parasporin-4 Diet in Mice

“…At present, 19 parasporins have been designated into six first rank levels by the Committee of Parasporin Classification and Nomenclature [5]. Moreover, some parasporin-like proteins without registration have been reported all over the world [6,7,8]. …”