BIOSORPTION OF HEAVY METALS BY A MODEL BACTERIAL VIRUS, ESHERICHIA COLI BACTERIOPHAGE T4

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 – 300 µM at 24°C). The Freundlich isotherm reasonably describes the sorption data, with an R-square of 0.97. Here, the value of n is less than 1. This indicates that the sorption sites on the surface of phage T4 are heterogeneous, with varied sorption energies for zinc. This is supported by the identification of the Hoc and Soc proteins on the surface of the capsid. These 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. Phage decay can alter the available surface area for metal adsorption. Interestingly, the presence of 100 µM Zn²⁺ significantly increased infectivity relative to unamended controls (ANOVA p<0.05), which indicates that Zn²⁺ 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.