Biosorption of Heavy Metals onto the Surface of Bacteriophage T4

Authors

Zheng Huan Tan, University of Nebraska-LincolnFollow

Date of this Version

Spring 4-25-2014

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Biological Sciences, Under the Supervision of Professor Karrie A. Weber. Lincoln, Nebraska: May, 2014

Copyright (c) 2014 Zheng Huan Tan

Abstract

Biosorption of heavy metals by bacterial and eukaryotic cell surfaces and the subsequent transport in aqueous environments is well recognized. However, very little is known about the roles viruses play in biosorption. Viruses outnumber prokaryotes and eukaryotes in environmental systems. These organisms represent abundant nanoparticulate organic colloids with reactive surfaces. Here we conducted a series of experiments to assess the biosorption potential of Escherichia coli bacteriophage T4. Adsorption of a heavy metal, Zn²⁺, to the surface of phage T4 was tested in a series of purified phage/metal solutions (0 µM – 1000 µM at 23°C). The Langmuir isotherm reasonably describes the sorption data, with an R-square of 0.8116. The Langmuir constant was determined to be 0.01265 which demonstrates that the adsorption of zinc onto the surface of phage T4 does occur, but not at a rapid rate. Studies have shown that the phage T4 capsid proteins possess negatively charged binding sites, which are the C-terminus for Soc and the N-terminus for Hoc. These two sites were proven to be biologically active and are able to bind certain proteins and antibodies. Thus, it is likely that these sites adsorb cations. Zeta potential analysis demonstrated phage T4 (10¹⁰ VLPs mL^-1) not exposed to zinc at pH 7.0 to be approximately -11.48 ± 1.16 mV. These results demonstrate the surface of phage T4 is naturally electronegative, which supports the capability of the surface of phage T4 to adsorb metal cations. This was subsequently demonstrated when the zeta potential shifted to -2.96 ± 1.60mV at pH 7.0 and exposure of 10¹⁰ VLPs mL^-1 to 150µM Zn²⁺, which suggests that adsorption of Zn²⁺ ions onto the phage resulted in the neutralization of negative charges on the phage surface. The effects of pH have been determined to have an effect on the adsorption of Zn²⁺ onto the surface of phage T4. Zn²⁺ adsorption is at a minimum when exposed to acidic pH and the amount of Zn²⁺ adsorbed increases with the rise of pH until a pH of 7.5, where precipitation of zinc hydroxide begins to occur and interferes with the adsorption process. Phage decay can alter the available surface area for metal adsorption. Interestingly, the presence of 150 µM Zn²⁺ significantly increased infectivity relative to unamended controls (ANOVA p2+ enhances phage T4 infectivity. Together, the results suggest that the sorption of metals to the surface of viruses could not only contribute to nanoparticulate metal transport but also enhance infectivity that contributes to cell lysis in environmental systems.

Advisor: Karrie A. Weber