Genus-Wide Physicochemical Evidence of Extracellular Crystalline Silver Nanoparticles Biosynthesis by Morganella spp. Rasesh Y. Parikh 1 , Rajesh Ramanathan 2 , Peter J. Coloe 2 , Suresh K. Bhargava 2 , Milind S. Patole 1 , Yogesh S. Shouche 1 *, Vipul Bansal 2 * 1 National Centre for Cell Science, Pune University Campus, Pune, India, 2 School of Applied Sciences, RMIT University, Melbourne, Victoria, Australia Abstract This study was performed to determine whether extracellular silver nanoparticles (AgNPs) production is a genus-wide phenotype associated with all the members of genus Morganella, or only Morganella morganii RP-42 isolate is able to synthesize extracellular Ag nanoparticles. To undertake this study, all the available Morganella isolates were exposed to Ag + ions, and the obtained nanoproducts were thoroughly analyzed using physico-chemical characterization tools such as transmission electron microscopy (TEM), UV-visible spectrophotometry (UV-vis), and X-ray diffraction (XRD) analysis. It was identified that extracellular biosynthesis of crystalline silver nanoparticles is a unique biochemical character of all the members of genus Morganella, which was found independent of environmental changes. Significantly, the inability of other closely related members of the family Enterobacteriaceae towards AgNPs synthesis strongly suggests that AgNPs synthesis in the presence of Ag + ions is a phenotypic character that is uniquely associated with genus Morganella. Citation: Parikh RY, Ramanathan R, Coloe PJ, Bhargava SK, Patole MS, et al. (2011) Genus-Wide Physicochemical Evidence of Extracellular Crystalline Silver Nanoparticles Biosynthesis by Morganella spp.. PLoS ONE 6(6): e21401. doi:10.1371/journal.pone.0021401 Editor: Dimitris Fatouros, Aristotle University of Thessaloniki, Greece Received October 20, 2010; Accepted June 1, 2011; Published June 21, 2011 Copyright: ß 2011 Parikh et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported in part by the Australian Research Council (ARC) Discovery grant and an APD Fellowship to V.B. (DP0988099), and an Endeavour Research Award to R.Y.P. from the Department of Education, Employment and Workplace Relations (DEEWR), Commonwealth of Australia to pursue this work at RMIT University, Australia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: yogesh@nccs.res.in (YSS); vipul.bansal@rmit.edu.au (VB) Introduction As nanotechnology is emerging as an interdisciplinary field with potential to influence various aspects of human life through a myriad of applications, biological synthesis of nanomaterials is gaining particular attention as a rapidly growing discipline of Bio- nanotechnology with an enormous application potential in the coming future [1,2]. There has been a strong interest in developing environmentally benign protocols for biological synthesis of nanomaterials that do not involve toxic chemicals in synthesis process. As demonstrated previously by our group and others [1–4], this has been successfully achieved by biological synthesis of various metal (Au [5–7], Ag [8–12], and Pt [13]), metal oxide (silica [14–18], titania [17], zirconia [19], magnetite [20–21] and barium titanate [22]), and metal sulphide (CdS [23], and Fe 2 S 3 [21]) nanoparticles by using prokaryotic as well as eukaryotic organisms including bacteria [4–5,9–10,12,21,23], fungi [7–8,14–17,19–20,22], and plants [6,11,13]. However, among various organisms studied until to date, prokaryotes remain the choice of organism for biological synthesis of nanomaterials [4–5,9–10,12,21,23]. This is predominantly be- cause prokaryotes offer well-defined advantages over eukaryotic organisms such as easy handling, ease of downstream processing and ease of genetic manipulation. However, the full potential of prokaryotic organisms for biological synthesis of nanoparticles can only be realized when plausible biochemical mechanism of nanoparticle synthesis is clearly understood. Among synthesis of different nanoparticles by various microorganisms, bacterial synthesis of silver nanoparticles (AgNPs) is particularly attractive from microbiology perspective due to existence of well-known silver resistance machinery in few silver resistant bacterial species, thus making their study significantly important for biomedical applications [10]. Moreover, silver nanoparticles have remained an attractive choice of nanomaterial because of their ability of encompassing broad application area from electronics to medicine to food technology [3–4,24–30]. Recently, in an attempt to understand the biomolecular mechanism of extracellular AgNPs synthesis, we demonstrated that Morganella morganii strain RP-42 isolate [10] was capable of synthesizing AgNPs extracellularly, and explored the phenotypic and genotypic characters of putative silver resistant machinery in Morganella sp. RP-42 [10]. It, however, remains an established fact that microbial physiology tends to evolve rapidly to the environmental changes to increase the chances of survival. To understand AgNPs synthesis by Morganella in a more clear way, it was found significantly important to evaluate whether the AgNPs synthesis was an adaptive physiology of Morganella sp. strain RP-42 as a result of environmental factors or it was independent to that [12]. In the present study, we aim to further strengthen the understanding of AgNPs synthesis in Morganella, and validate whether extracellular AgNPs synthesis in the presence of Ag + ions is a genus-wide phenotype in Morganella spp. This has been achieved by performing a detailed time-dependent UV-visible absorption spectroscopy study with respect to AgNPs synthesis PLoS ONE | www.plosone.org 1 June 2011 | Volume 6 | Issue 6 | e21401