title: Lysinibacillus sphaericus binary toxin induces apoptosis in susceptible Culex quinquefasciatus larvae.
abstract: During sporulation, a Gram-positive bacterium Lysinibacillus sphaericus (Ls) produces the mosquito larvicidal binary toxin composed of 2 subunits, BinA and BinB. Full toxicity against Culex and Anopheles mosquito larvae is achieved when both subunits are administered together at equimolar amounts. Although cellular responses to Bin toxin have been reported in previous studies, it remains essential to extensively examine the cytopathic effects in vivo to define the underlying mechanism of larval death. In this study, 4th instar Culex quinquefasciatus larvae fed with different doses of Bin toxin were analyzed both for ultrastructural as well as biochemical effects. Typical morphological changes consistent with apoptosis were observed in mosquito larvae exposed to Bin toxin, including mitochondrial swelling, chromatin condensation, cytoplasmic vacuolization and apoptotic cell formation. Bin toxin also induced the activation of caspase-9 and caspase-3 in larval midgut cells. Our current observations thus suggest that Bin toxin triggers apoptosis via an intrinsic or mitochondrial pathway in vivo, possibly contributing to larval death.
authors.affiliation: Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon, Nakhon Pathom 73170, Thailand.
authors.forename: Chontida
authors.initials: C
authors.lastname: Tangsongcharoen
authors.affiliation: Department of Pathology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
authors.forename: Nusara
authors.initials: N
authors.lastname: Chomanee
authors.affiliation: National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Pahonyothin Road, Khlong Nueng, Khlong Luang, Pathum Thani 12120, Thailand.
authors.forename: Boonhiang
authors.initials: B
authors.lastname: Promdonkoy
authors.affiliation: Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon, Nakhon Pathom 73170, Thailand. Electronic address: panadda.boo@mahidol.ac.th.
authors.forename: Panadda
authors.initials: P
authors.lastname: Boonserm
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001427:Bacterial Toxins / Q000494:pharmacology*; D003465:Culex / Q000187:drug effects* / Q000382:microbiology; D006090:Gram-Negative Bacteria; D020287:In Situ Nick-End Labeling; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects; D046529:Microscopy, Electron, Transmission
chemical_list: D001427:Bacterial Toxins; D007306:Insecticides
keywords: Apoptosis; Binary toxin; Lysinibacillus sphaericus; Mitochondrial swelling