title: Intracellular siderophore but not extracellular siderophore is required for full virulence in Metarhizium robertsii.
abstract: Efficient iron acquisition mechanisms are fundamental for microbial survival in the environment and for pathogen virulence within their hosts. M. robertsii produces two known iron-binding natural products: metachelins, which are used to scavenge extracellular iron, and ferricrocin, which is strictly intracellular. To study the contribution of siderophore-mediated iron uptake and storage to M. robertsii fitness, we generated null mutants for each siderophore synthase gene (mrsidD and mrsidC, respectively), as well as for the iron uptake transcriptional repressor mrsreA. All of these mutants showed impaired germination speed, differential sensitivity to hydrogen peroxide, and differential ability to overcome iron chelation on growth-limiting iron concentrations. RT-qPCR data supported regulation of mrsreA, mrsidC, and mrsidD by supplied iron in vitro and during growth within the insect host, Spodoptera exigua. We also observed strong upregulation of the insect iron-binding proteins, transferrins, during infection. Insect bioassays revealed that ferricrocin is required for full virulence against S. exigua; neither the loss of metachelin production nor the deletion of the transcription factor mrsreA significantly affected M. robertsii virulence.
authors.affiliation: School of Integrative Plant Science - Plant Pathology and Plant-Microbe Biology Section, Cornell University, Ithaca, NY 14853, United States. Electronic address: bdd1@cornell.edu.
authors.forename: Bruno
authors.initials: B
authors.lastname: Giuliano Garisto Donzelli
authors.affiliation: USDA ARS, Robert W. Holley Center for Agriculture and Health, 538 Tower Road, Ithaca, NY 14853, United States.
authors.forename: Donna M
authors.initials: DM
authors.lastname: Gibson
authors.affiliation: USDA ARS, Robert W. Holley Center for Agriculture and Health, 538 Tower Road, Ithaca, NY 14853, United States.
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Krasnoff
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005291:Ferrichrome / Q000031:analogs & derivatives; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D007313:Insecta / Q000382:microbiology; D042541:Intracellular Space; D007501:Iron / Q000378:metabolism; D052981:Metarhizium / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism* / Q000472:pathogenicity; D005810:Multigene Family; D009154:Mutation; D010641:Phenotype; D017384:Sequence Deletion; D017262:Siderophores / Q000737:chemistry / Q000378:metabolism*; D014774:Virulence / Q000235:genetics
chemical_list: D005656:Fungal Proteins; D017262:Siderophores; D005291:Ferrichrome; C021678:ferricrocin; D006861:Hydrogen Peroxide; D007501:Iron
keywords: Ferricrocin; GATA transcriptional repressor; Iron; Metachelins; Siderophore; Virulence