Toward revealing the controversy of bacterial biosynthesis versus bactericidal properties of silver nanoparticles (AgNPs
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ORIGINAL PAPER
Toward revealing the controversy of bacterial biosynthesis versus bactericidal properties of silver nanoparticles (AgNPs): bacteria and other microorganisms do not per se viably synthesize AgNPs Fatthy Mohamed Morsy
Received: 25 October 2014 / Revised: 6 January 2015 / Accepted: 20 February 2015 © Springer-Verlag Berlin Heidelberg 2015
Abstract In the last two decades, a large number of literature had focused on the biosynthesis of silver nanoparticles (AgNPs) from silver ions by bacteria and other microorganisms. This study infers that bacteria and other microorganisms do not per se synthesize AgNPs. All tested auto- and heterotrophic microorganisms in this study were killed by silver ions and could not as viable cells produce AgNPs. Microbial cell viability represented in colonyforming units and metabolic viability represented in aerobic respiration in all investigated microorganisms as well as photosynthesis in photoautotrophic microorganisms ceased by silver ions too early before AgNPs formation. The time required for AgNPs synthesis inversely related to the incubation temperature of the investigated microorganisms with silver ions where it requires only few minutes for nanoparticles formation at high temperature or autoclaving. The minimum inhibitory and minimum bactericidal and fungicidal concentrations of silver ions were significantly lower than AgNPs, indicating that silver ions are more efficient antimicrobial. The results presented in this study indicate that formation of AgNPs by eubacteria, cyanobacteria and fungi is not a vitally regulated cellular metabolic process and the mechanism occurs via bioreduction of silver ions to nanoparticles by organics released from the dead cells.
Communicated by Erko Stackebrandt. F. M. Morsy Biology Department, Faculty of Science, Taibah University, Medina, Saudi Arabia F. M. Morsy (*) Botany and Microbiology Department, Faculty of Science, Assiut University, Assiut 71516, Egypt e-mail: [email protected]
Keywords Antibacterial agents · Antimicrobial agents · Biosynthesis · Nanoparticles · Silver
Introduction Over the past few decades, nanoparticles, with at least one dimension less than 100 nm, of metals attracted high attention for its new applications in various fields of industry. Among these nanomaterials, silver nanoparticles (AgNPs) seem to have attracted the most interest in terms of its potential applications. Chemical, physical and biological syntheses of AgNPs are hot topics of research due to the wide range of AgNPs applications and their antibacterial, antifungal and antiviral activities (Kim et al. 2007; Pal et al. 2007; Rai et al. 2009; et al. De Gusseme et al. 2010; Govindaraju et al. 2011; Lara et al. 2011; Brandt et al. 2012; Kim et al. 2012; Mohanty et al. 2012; Tamboli and Lee 2013; Eckhardt et al. 2013; Lok et al. 2014). Because of their antimicrobial properties, AgNPs are incorporated in apparel, footwear, paints, wound dressings, appliances, cosmetics and plastics (Sharma et al. 2009; Li et al. 2010). In spite of the an
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