title: Tribolium castaneum defensins are primarily active against Gram-positive bacteria.
abstract: The red flour beetle Tribolium castaneum is a destructive insect pest of stored food and feed products, and a model organism for development, evolutionary biology and immunity. The insect innate immune system includes antimicrobial peptides (AMPs) with a wide spectrum of targets including viruses, bacteria, fungi and parasites. Defensins are an evolutionarily-conserved class of AMPs and a potential new source of antimicrobial agents. In this context, we report the antimicrobial activity, phylogenetic and structural properties of three T. castaneum defensins (Def1, Def2 and Def3) and their relevance in the immunity of T. castaneum against bacterial pathogens. All three recombinant defensins showed bactericidal activity against Micrococcus luteus and Bacillus thuringiensis serovar tolworthi, but only Def1 and Def2 showed a bacteriostatic effect against Staphylococcus epidermidis. None of the defensins showed activity against the Gram-negative bacteria Escherichia coli and Pseudomonas entomophila or against the yeast Saccharomyces cerevisiae. All three defensins were transcriptionally upregulated following a bacterial challenge, suggesting a key role in the immunity of T. castaneum against bacterial pathogens. Phylogenetic analysis showed that defensins from T. castaneum, mealworms, Udo longhorn beetle and houseflies cluster within a well-defined clade of insect defensins. We conclude that T. castaneum defensins are primarily active against Gram-positive bacteria and that other AMPs may play a more prominent role against Gram-negative species.
authors.affiliation: Fraunhofer Institute for Molecular Biology and Applied Ecology, Department of Bioresources, Winchester Strasse, D-35394 Giessen, Germany. Electronic address: miray.tonk@ime.fraunhofer.de.
authors.forename: Miray
authors.initials: M
authors.lastname: Tonk
authors.affiliation: Fraunhofer Institute for Molecular Biology and Applied Ecology, Department of Bioresources, Winchester Strasse, D-35394 Giessen, Germany. Electronic address: eileen.knorr@ime.fraunhofer.de.
authors.forename: Eileen
authors.initials: E
authors.lastname: Knorr
authors.affiliation: Center for Infection and Immunity of Lille (CIIL), INSERM U1019 - CNRS UMR 8204, Université Lille Nord de France, Institut Pasteur de Lille, Lille, France. Electronic address: cabezasalejandrocruz@gmail.com.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Cabezas-Cruz
authors.affiliation: Biology Centre of the AS CR, Institute of Parasitology, Branišovská 31, 37005 České Budějovice, Czech Republic. Electronic address: valdjj@gmail.com.
authors.forename: James J
authors.initials: JJ
authors.lastname: Valdés
authors.affiliation: Fraunhofer Institute for Molecular Biology and Applied Ecology, Department of Bioresources, Winchester Strasse, D-35394 Giessen, Germany. Electronic address: ckollewe@web.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Kollewe
authors.affiliation: Fraunhofer Institute for Molecular Biology and Applied Ecology, Department of Bioresources, Winchester Strasse, D-35394 Giessen, Germany; Institute for Insect Biotechnology, Justus-Liebig-University of Giessen, Heinrich-Buff-Ring 26-32, D-35392 Giessen, Germany. Electronic address: andreas.vilcinskas@agrar.uni-giessen.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Vilcinskas
mesh_terms: D000818:Animals; D019295:Computational Biology; D023082:Defensins / Q000502:physiology*; D005786:Gene Expression Regulation; D006094:Gram-Positive Bacteria / Q000276:immunology*; D007113:Immunity, Innate; D019476:Insect Proteins / Q000502:physiology*; D010802:Phylogeny; D014231:Tribolium / Q000276:immunology*
chemical_list: D023082:Defensins; D019476:Insect Proteins
keywords: Antimicrobial peptides; Defensin; Gram-positive bacteria; Innate immunity; Insects; Tribolium castaneum