title: Cationic Peptides Facilitate Iron-induced Mutagenesis in Bacteria.
abstract: Pseudomonas aeruginosa is the causative agent of chronic respiratory infections and is an important pathogen of cystic fibrosis patients. Adaptive mutations play an essential role for antimicrobial resistance and persistence. The factors that contribute to bacterial mutagenesis in this environment are not clear. Recently it has been proposed that cationic antimicrobial peptides such as LL-37 could act as mutagens in P. aeruginosa. Here we provide experimental evidence that mutagenesis is the product of a joint action of LL-37 and free iron. By estimating mutation rate, mutant frequencies and assessing mutational spectra in P. aeruginosa treated either with LL-37, iron or a combination of both we demonstrate that mutation rate and mutant frequency were increased only when free iron and LL-37 were present simultaneously. Colistin had the same effect. The addition of an iron chelator completely abolished this mutagenic effect, suggesting that LL-37 enables iron to enter the cells resulting in DNA damage by Fenton reactions. This was also supported by the observation that the mutational spectrum of the bacteria under LL-37-iron regime showed one of the characteristic Fenton reaction fingerprints: C to T transitions. Free iron concentration in nature and within hosts is kept at a very low level, but the situation in infected lungs of cystic fibrosis patients is different. Intermittent bleeding and damage to the epithelial cells in lungs may contribute to the release of free iron that in turn leads to generation of reactive oxygen species and deterioration of the respiratory tract, making it more susceptible to the infection.
authors.affiliation: Evolutionary Biology, Institute for Biology, Free University Berlin, Berlin, Germany.
authors.forename: Alexandro
authors.initials: A
authors.lastname: Rodríguez-Rojas
authors.affiliation: Evolutionary Biology, Institute for Biology, Free University Berlin, Berlin, Germany.
authors.forename: Olga
authors.initials: O
authors.lastname: Makarova
authors.affiliation: Evolutionary Biology, Institute for Biology, Free University Berlin, Berlin, Germany.
authors.forename: Uta
authors.initials: U
authors.lastname: Müller
authors.affiliation: Evolutionary Biology, Institute for Biology, Free University Berlin, Berlin, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Rolff
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000235:genetics* / Q000494:pharmacology; D003550:Cystic Fibrosis / Q000188:drug therapy / Q000235:genetics; D004249:DNA Damage / Q000187:drug effects; D004352:Drug Resistance, Microbial / Q000235:genetics*; D004357:Drug Synergism; D006801:Humans; D007501:Iron / Q000494:pharmacology; D016296:Mutagenesis / Q000187:drug effects*; D009154:Mutation; D059645:Mutation Rate; D011552:Pseudomonas Infections / Q000188:drug therapy / Q000235:genetics* / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics* / Q000472:pathogenicity; D017382:Reactive Oxygen Species / Q000378:metabolism; D054804:Cathelicidins
chemical_list: D023181:Antimicrobial Cationic Peptides; D017382:Reactive Oxygen Species; D007501:Iron; D054804:Cathelicidins