Imposed Environmental Stresses Facilitate Cell-free Nanoparticle Formation by Deinococcus radiodurans.

by Chen, A; Contreras, LM; Keitz, BK

Applied and Environmental Microbiology; Jul 7 2017; doi: 10.1128/AEM.00798-17

The biological synthesis of metal nanoparticles has been examined in a wide range of organisms due to increased interest in green synthesis and environmental remediation applications involving heavy metal ion contamination. Deinococcus radiodurans is particularly attractive for environmental remediation involving metal reduction due to its high resistance to radiation and other environmental stresses. However, few studies have thoroughly examined the relationship between environmental stresses and their resulting effect on nanoparticle biosynthesis. In this work, we demonstrate cell-free nanoparticle production and study the effect of metal stressor concentration and identity, temperature, pH, and oxygenation on the production of extracellular silver nanoparticles by D. radiodurans R1. We also report the synthesis of bimetallic silver and gold nanoparticles following addition of a metal stressor (silver or gold), highlighting how production of these particles is enabled through application of environmental stresses. Additionally, we found that both the morphology and size of monometallic and bimetallic nanoparticles are dependent on the environmental stresses imposed on the cells. The nanoparticles produced by D. radiodurans exhibit antimicrobial activity comparable to pure silver nanoparticles and display catalytic activity comparable to pure gold nanoparticles. Overall, we demonstrate that biosynthesized nanoparticle properties can be partially controlled through tuning of applied environmental stresses and provide insight into how their application may impact nanoparticle production in D. radiodurans during bioremediation.IMPORTANCE Biosynthetic production of nanoparticles has recently gained prominence as a solution to rising concerns regarding increased bacterial resistance to antibiotics and a desire for environmentally-friendly methods of bioremediation and chemical synthesis. To date, a range of organisms have been utilized for nanoparticle formation. The extremophile D. radiodurans, which can withstand significant environmental stresses and is therefore more robust for metal reduction applications, has yet to be exploited for this purpose. Thus, this work improves our understanding of the impact of environmental stresses on biogenic nanoparticle morphology and composition during metal reduction processes in this organism. This work also contributes towards enhancing the controlled synthesis of nanoparticles with specific attributes and functions using biological systems.

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