title: Polysaccharide-based silver nanoparticles synthesized by Klebsiella oxytoca DSM 29614 cause DNA fragmentation in E. coli cells.
abstract: Silver nanoparticles (AgNPs), embedded into a specific exopolysaccharide (EPS), were produced by Klebsiella oxytoca DSM 29614 by adding AgNO3 to the cultures during exponential growth phase. In particular, under aerobic or anaerobic conditions, two types of silver nanoparticles, named AgNPs-EPS(aer) and the AgNPs-EPS(anaer), were produced respectively. The effects on bacterial cells was demonstrated by using Escherichia coli K12 and Kocuria rhizophila ATCC 9341 (ex Micrococcus luteus) as Gram-negative and Gram-positive tester strains, respectively. The best antimicrobial activity was observed for AgNPs-EPS(aer), in terms of minimum inhibitory concentrations and minimum bactericidal concentrations. Observations by transmission electron microscopy showed that the cell morphology of both tester strains changed during the exposition to AgNPs-EPS(aer). In particular, an electron-dense wrapped filament was observed in E. coli cytoplasm after 3 h of AgNPs-EPS(aer) exposition, apparently due to silver accumulation in DNA, and both E. coli and K. rhizophila cells were lysed after 18 h of exposure to AgNPs-EPS(aer). The DNA breakage in E. coli cells was confirmed by the comparison of 3-D fluorescence spectra fingerprints of DNA. Finally the accumulation of silver on DNA of E. coli was confirmed directly by a significant Ag(+) release from DNA, using the scanning electrochemical microscopy and the voltammetric determinations.
authors.affiliation: Dipartimento di Scienze Molecolari e Nanosistemi, University Cà Foscari of Venice, Via Torino 155, 30172, Venice, Italy. baldi@unive.it.
authors.forename: Franco
authors.identifier: http://orcid.org/0000-0003-3190-9009
authors.initials: F
authors.lastname: Baldi
authors.affiliation: Dipartimento di Scienze Molecolari e Nanosistemi, University Cà Foscari of Venice, Via Torino 155, 30172, Venice, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Daniele
authors.affiliation: Dipartimento di Scienze Molecolari e Nanosistemi, University Cà Foscari of Venice, Via Torino 155, 30172, Venice, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Gallo
authors.affiliation: Dipartimento di Scienze Molecolari e Nanosistemi, University Cà Foscari of Venice, Via Torino 155, 30172, Venice, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Paganelli
authors.affiliation: Dipartimento di Scienze Ambientali, Infomatica e Statistica, University Cà Foscari of Venice, Via Torino 155, 30172, Venice, Italy.
authors.forename: Dario
authors.initials: D
authors.lastname: Battistel
authors.affiliation: SCSOP, Via Bornò 5, 23896, Sirtori, LC, Italy.
authors.forename: Oreste
authors.initials: O
authors.lastname: Piccolo
authors.affiliation: Dipartimento Scienze della Vita, University of Siena, Via Mattioli 4, 53100, Siena, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Faleri
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), University of Palermo, Viale delle Scienze - ed. 16, 90128, Palermo, Italy.
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Puglia
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), University of Palermo, Viale delle Scienze - ed. 16, 90128, Palermo, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Gallo
mesh_terms: D000900:Anti-Bacterial Agents / Q000096:biosynthesis / Q000494:pharmacology*; D019149:Bioreactors; D053938:DNA Fragmentation; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D041121:Klebsiella oxytoca / Q000378:metabolism*; D053768:Metal Nanoparticles; D008826:Microbial Sensitivity Tests; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis / Q000494:pharmacology*; D012834:Silver / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D011135:Polysaccharides, Bacterial; D012834:Silver
keywords: Antimicrobial activity; Cell lysis; Silver exopolysaccharide nanoparticles; Silver in DNA; Silver release