title: A Bacillus thuringiensis S-layer protein involved in toxicity against Epilachna varivestis (Coleoptera: Coccinellidae).
abstract: The use of Bacillus thuringiensis as a biopesticide is a viable alternative for insect control since the insecticidal Cry proteins produced by these bacteria are highly specific; harmless to humans, vertebrates, and plants; and completely biodegradable. In addition to Cry proteins, B. thuringiensis produces a number of extracellular compounds, including S-layer proteins (SLP), that contribute to virulence. The S layer is an ordered structure representing a proteinaceous paracrystalline array which completely covers the surfaces of many pathogenic bacteria. In this work, we report the identification of an S-layer protein by the screening of B. thuringiensis strains for activity against the coleopteran pest Epilachna varivestis (Mexican bean beetle; Coleoptera: Coccinellidae). We screened two B. thuringiensis strain collections containing unidentified Cry proteins and also strains isolated from dead insects. Some of the B. thuringiensis strains assayed against E. varivestis showed moderate toxicity. However, a B. thuringiensis strain (GP1) that was isolated from a dead insect showed a remarkably high insecticidal activity. The parasporal crystal produced by the GP1 strain was purified and shown to have insecticidal activity against E. varivestis but not against the lepidopteran Manduca sexta or Spodoptera frugiperda or against the dipteran Aedes aegypti. The gene encoding this protein was cloned and sequenced. It corresponded to an S-layer protein highly similar to previously described SLP in Bacillus anthracis (EA1) and Bacillus licheniformis (OlpA). The phylogenetic relationships among SLP from different bacteria showed that these proteins from Bacillus cereus, Bacillus sphaericus, B. anthracis, B. licheniformis, and B. thuringiensis are arranged in the same main group, suggesting similar origins. This is the first report that demonstrates that an S-layer protein is directly involved in toxicity to a coleopteran pest.
authors.affiliation: Instituto de Biotecnología, UNAM, Ap. Postal 510-3, Cuernavaca 62250, Morelos, México.
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Peña
authors.forename: Juan
authors.initials: J
authors.lastname: Miranda-Rios
authors.forename: Gustavo
authors.initials: G
authors.lastname: de la Riva
authors.forename: Liliana
authors.initials: L
authors.lastname: Pardo-López
authors.forename: Mario
authors.initials: M
authors.lastname: Soberón
authors.forename: Alejandra
authors.initials: A
authors.lastname: Bravo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001413:Bacillus thuringiensis / Q000145:classification / Q000302:isolation & purification / Q000378:metabolism* / Q000472:pathogenicity; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D003001:Cloning, Molecular; D001517:Coleoptera / Q000187:drug effects*; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D008969:Molecular Sequence Data; D010572:Pest Control, Biological; D010802:Phylogeny; D011817:Rabbits; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; C055764:S-layer proteins