title: Francisella is sensitive to insect antimicrobial peptides.
abstract: Francisella tularensis causes the zoonotic disease tularemia. Arthropod vectors are important transmission routes for the disease, although it is not known how Francisella survives the efficient arthropod immune response. Here, we used Drosophila melanogaster as a model host for Francisella infections and investigated whether the bacteria are resistant to insect humoral immune responses, in particular to the antimicrobial peptides (AMPs) secreted into the insect hemolymph. Moreover, we asked to what extent such resistance might depend on lipopolysaccharide (LPS) structure and surface characteristics of the bacteria. We analyzed Francisella novicida mutant strains in genes, directly or indirectly involved in specific steps of LPS biosynthesis, for virulence in wild-type and Relish(E20) immune-deficient flies, and tested selected mutants for sensitivity to AMPs in vitro. We demonstrate that Francisella is sensitive to specific fly AMPs, i.e. Attacin, Cecropin, Drosocin and Drosomycin. Furthermore, six bacterial genes, kpsF, manB, lpxF, slt, tolA and pal, were found to be required for resistance to Relish-dependent immune responses, illustrating the importance of structural details of Francisella lipid A and Kdo core for interactions with AMPs. Interestingly, a more negative surface charge and lack of O-antigen did not render mutant bacteria more sensitive to cationic AMPs and did not attenuate virulence in flies.
authors.affiliation: Department of Clinical Microbiology, Umeå University, Umeå, Sweden.
authors.forename: Malin
authors.initials: M
authors.lastname: Vonkavaara
authors.forename: Shaikh Terkis Islam
authors.initials: ST
authors.lastname: Pavel
authors.forename: Kathrin
authors.initials: K
authors.lastname: Hölzl
authors.forename: Roland
authors.initials: R
authors.lastname: Nordfelth
authors.forename: Anders
authors.initials: A
authors.lastname: Sjöstedt
authors.forename: Svenja
authors.initials: S
authors.lastname: Stöven
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000235:genetics / Q000378:metabolism*; D001179:Arthropod Vectors / Q000276:immunology; D004195:Disease Models, Animal; D029721:Drosophila Proteins / Q000235:genetics; D004331:Drosophila melanogaster / Q000276:immunology; D005604:Francisella tularensis / Q000276:immunology*; D005798:Genes, Bacterial / Q000235:genetics; D007109:Immunity / Q000235:genetics; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D008050:Lipid A / Q000737:chemistry / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D030781:Organisms, Genetically Modified; D013400:Sugar Acids / Q000737:chemistry / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics; D014406:Tularemia / Q000276:immunology*
chemical_list: D023181:Antimicrobial Cationic Peptides; D029721:Drosophila Proteins; D019476:Insect Proteins; D008050:Lipid A; D008070:Lipopolysaccharides; C101626:Rel protein, Drosophila; D013400:Sugar Acids; D014157:Transcription Factors; C120356:3-deoxy-manno-oct-2-ulopyranosonic acid