title: Medium from γ-irradiated Escherichia coli bacteria stimulates a unique immune response in Drosophila cells.
abstract: It is well known that γ-irradiated, non-dividing bacteria can elicit potent immune responses in mammals. Compared to traditional heat or chemical inactivation of microbes, γ-irradiation likely preserves metabolic activity and antigenic features to a larger extent. We have previously shown that antimicrobial peptides are induced in Drosophila by peptidoglycan fragments secreted into the medium of exponentially growing bacterial cultures. In this study, we γ-irradiated Escherichiacoli cells at a dose that halted cell division. The temporal synthesis and release of peptidoglycan fragments were followed as well as the potential of bacterial supernatants to induce immune responses in Drosophila S2 cells. We demonstrate that peptidoglycan synthesis continues for several days post irradiation and that monomeric peptidoglycan is shed into the medium. Whole transcriptome analysis revealed a strong immune response against the bacterial medium. The response to medium taken directly post irradiation shows a large overlap to that of peptidoglycan. Medium from prolonged bacterial incubation does, however, stimulate a selective set of immune genes. A shift towards a stress response was instead observed with a striking induction of several heat shock proteins. Our findings suggest that γ-irradiated bacteria release elicitors that stimulate a novel response in Drosophila.
authors.affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20 C, 106 91 Stockholm, Sweden.
authors.forename: Bo G
authors.initials: BG
authors.lastname: Lindberg
authors.affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20 C, 106 91 Stockholm, Sweden.
authors.forename: Sandra
authors.initials: S
authors.lastname: Oldenvi
authors.affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Svante Arrhenius väg 20 C, 106 91 Stockholm, Sweden. Electronic address: hakan.steiner@su.se.
authors.forename: Håkan
authors.initials: H
authors.lastname: Steiner
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000096:biosynthesis / Q000235:genetics; D002460:Cell Line; D003470:Culture Media; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000235:genetics; D004331:Drosophila melanogaster / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D004926:Escherichia coli / Q000166:cytology / Q000528:radiation effects*; D005720:Gamma Rays; D015870:Gene Expression / Q000276:immunology; D056724:Immunity, Humoral
chemical_list: D023181:Antimicrobial Cationic Peptides; D003470:Culture Media; D029721:Drosophila Proteins
keywords: Antimicrobial peptides; Heat shock proteins; Peptidoglycan; S2 cells