Controlling gold nanoparticle biogenesis in the bacterium enterobacter sp. Pb204

Ho, Nicholas Ryan
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Research into the synthesis of gold nanoparticles (AuNPs) has increased in the past few decades due to their wide range of potential applications, with increased emphasis placed on the greener synthesis of AuNPs. A promising method of synthesis is bacterial synthesis but one of the largest obstacles faced by this method is the large variability in the shape and size of AuNPs. To this end, the aim of this study was to improve the uniformity of AuNPs synthesised by a bacterium isolated from acid mine decant on the West Rand of Gauteng, South Africa, (26°06'26.8"S 27°43'20.2"E) (Enterobacter sp. Pb204) through alteration of reaction parameters as well as the determination of possible genetic pathways responsible for AuNP synthesis. The following reaction parameters: growth media, biocatalyst ratio, temperature, pH and gold ion concentration were altered to determine their influence on AuNP synthesis by Enterobacter sp. Pb204. The AuNPs were analysed using ultravioletvisible spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. Following the optimisation of AuNP biogenesis in Enterobacter sp. Pb204, the whole genome of the bacterium was sequenced using the Illumina Hiseq (2500, California, USA). To produce uniformed spherical AuNPs, within a size range of 2 to 15 nm, the following parameters were identified: cell biocatalyst grown LB at a pH of 3, incubated at 37 °C with a chloroauric acid concentration of 1 mM for 24 hours. The whole genome analysis of Enterobacter sp. Pb204 revealed that it is a unique strain of Enterobacter xiangfangensis LMG 27195T and was therefore named E. xiangfangensis Pb204. Further analysis of E. xiangfangensis Pb204’s genome revealed that it possessed several unique metal resistance genes not found in the type strain. The majority of these genes were found on an integrated conjugative element (ICE). The presence of the ICE element, with the extra cargo genes, in E. xiangfangensis Pb204 may play a role in AuNP synthesis.
A dissertation submitted to the Faculty of Science of the University of Witwatersrand, Johannesburg, in fullfulfilment of the requirements for the degree of Master of Science, 2018
Ho, Nicholas Ryan, (2018) Controlling gold nanoparticle biogenesis in the bacterium Enterobacter sp. Pb204, University of the Witwatersrand, Johannesburg,