title: Midgut microbiota and host immunocompetence underlie Bacillus thuringiensis killing mechanism.
abstract: Bacillus thuringiensis is a widely used bacterial entomopathogen producing insecticidal toxins, some of which are expressed in insect-resistant transgenic crops. Surprisingly, the killing mechanism of B. thuringiensis remains controversial. In particular, the importance of the septicemia induced by the host midgut microbiota is still debated as a result of the lack of experimental evidence obtained without drastic manipulation of the midgut and its content. Here this key issue is addressed by RNAi-mediated silencing of an immune gene in a lepidopteran host Spodoptera littoralis, leaving the midgut microbiota unaltered. The resulting cellular immunosuppression was characterized by a reduced nodulation response, which was associated with a significant enhancement of host larvae mortality triggered by B. thuringiensis and a Cry toxin. This was determined by an uncontrolled proliferation of midgut bacteria, after entering the body cavity through toxin-induced epithelial lesions. Consequently, the hemolymphatic microbiota dramatically changed upon treatment with Cry1Ca toxin, showing a remarkable predominance of Serratia and Clostridium species, which switched from asymptomatic gut symbionts to hemocoelic pathogens. These experimental results demonstrate the important contribution of host enteric flora in B. thuringiensis-killing activity and provide a sound foundation for developing new insect control strategies aimed at enhancing the impact of biocontrol agents by reducing the immunocompetence of the host.
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy; silvia.caccia@unina.it f.pennacchio@unina.it.
authors: Silvia
authors: S
authors: Caccia
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy;
authors: Ilaria
authors: I
authors: Di Lelio
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy;
authors: Antonietta
authors: A
authors: La Storia
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy;
authors: Adriana
authors: A
authors: Marinelli
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy;
authors: Paola
authors: P
authors: Varricchio
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy;
authors: Eleonora
authors: E
authors: Franzetti
authors: Interdisciplinary Research Structure for Biotechnology and Biomedicine, University of Valencia, 46100 Burjassot, Spain;
authors: Núria
authors: N
authors: Banyuls
authors: Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy;
authors: Gianluca
authors: G
authors: Tettamanti
authors: Department of Biosciences, University of Milano, 20133 Milan, Italy;
authors: Morena
authors: M
authors: Casartelli
authors: Department of Biosciences, University of Milano, 20133 Milan, Italy;
authors: Barbara
authors: B
authors: Giordana
authors: Interdisciplinary Research Structure for Biotechnology and Biomedicine, University of Valencia, 46100 Burjassot, Spain;
authors: Juan
authors: J
authors: Ferré
authors: Institute of Biosciences and Bioresources, National Research Council of Italy, 80131 Naples, Italy.
authors: Silvia
authors: S
authors: Gigliotti
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy;
authors: Danilo
authors: 0000-0003-3061-9560
authors: D
authors: Ercolini
authors: Department of Agricultural Sciences, University of Napoli Federico II, 80055 Portici, Italy; silvia.caccia@unina.it f.pennacchio@unina.it.
authors: Francesco
authors: F
authors: Pennacchio
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000254:growth & development / Q000472:pathogenicity*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000096:biosynthesis*; D003013:Clostridium / Q000254:growth & development / Q000472:pathogenicity; D018556:Crops, Agricultural / Q000469:parasitology; D004731:Endotoxins / Q000096:biosynthesis*; D005786:Gene Expression Regulation; D006434:Hemocytes / Q000276:immunology / Q000382:microbiology; D006460:Hemolysin Proteins / Q000096:biosynthesis*; D007113:Immunity, Innate; D007165:Immunosuppression Therapy; D019476:Insect Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000276:immunology; D007422:Intestines / Q000276:immunology / Q000382:microbiology; D007814:Larva / Q000235:genetics / Q000276:immunology / Q000382:microbiology; D064307:Microbiota / Q000276:immunology*; D010572:Pest Control, Biological / Q000379:methods*; D034622:RNA Interference; D012330:RNA, Double-Stranded / Q000235:genetics / Q000378:metabolism; D012705:Serratia / Q000254:growth & development / Q000472:pathogenicity; D018411:Spodoptera / Q000235:genetics / Q000276:immunology* / Q000382:microbiology
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D019476:Insect Proteins; D012330:RNA, Double-Stranded; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: bioinsecticide; immunity; insect biocontrol; insect–pathogen interactions; pore-forming toxins