Localization Effect on the Metal Biosorption Capability of Recombinant Mammalian and Fish Metallothioneins in Escherichia coli

Abstract

In this study, we examined the expression of mammalian and fish metallothioneins (MTs) in Escherichia coli as a strategy to enhance metal biosorption efficiency of bacterial biosorbents for lead (Pb), copper (Cu), cadmium (Cd), and zinc (Zn). In addition, MT proteins were expressed in either the cytoplasmic or periplasmic compartment of host cells to explore the localization effect on metal biosorption. The results showed that MT expression led to a significant increase (5-210%) in overall biosorption efficiency (eta(ads)), especially for biosorption of Cd. The MT-driven improvement in metal biosorption relied more on the increase in the biosorption rates (r(2), a kinetic property) than on the equilibrium biosorption capacities (q(max), a thermodynamic property), despite a 10-45% and 30-80% increase in q(max) of Cd and Zn, respectively. Periplasmic expression of MTs appeared to be more effective in facilitating the metal-binding ability than the cytoplasmlic MT expression. Notably, disparity of the impacts on biosorption ability was observed for the origin of MT proteins, as human MT (MT1A) was the most effective biosorption stimulator compared to MTs originating from mouse (MT1) and fish (OmMT). Moreover, the overall biosorption efficiency (eta(ads)) of the MT-expressing recombinant biosorbents was found to be adsorbate-dependent: the eta(ads) values decreased in the order of Cd > Cu > Zn > Pb.

Bioaccumulation of Arsenic in recombinant Escherichia coli expressing human metallothionein

“…Besides, it needs no trans-membrane transportation of the heavy metals. Expression of MT in E.coli as fusions to membrane proteins was reported on Cd bioaccumulation [29,30]. A more than 5 fold increase of Cd binding capacity was obtained [31].…”

Gene Cloning, Protein Expression and Functional Analysis of a type 3 Metallothionein with Bioaccumulation Potential from Sonneratia alba

“…A reported method was used to analyze the bioaccumulation capacity of E. coli expressing SaMT3 [16]. After induction with 500 μM IPTG for 12 h, E. coli were centrifuged at 5,000 g for 10 min.…”

“…Similarly, exogenous expression KcMT2a from Kandelia candel also improved the metal tolerance ability of E. coli cells and metal-binding activities [33]. In order to better compare the bioaccumulation capacity of His and His fused SaMT3 protein, reported concentrations (250 μM, 500 μM, and 1,000 μM) and different time points were used (24 h, 48 h) [16]. These concentrations were frequently used in analyzing the metal-binding capacities of MTs [20].…”

Biosorption of nickel, chromium and zinc by MerP-expressing recombinant Escherichia coli

“…3 g dry weight/L) for the biosorption experiments. All the glassware used in the biosorption operations was treated with concentrated HNO 3 solution prior to each experiment to avoid possible adsorption of heavy metals on the surface of glass containers [2,4,32].…”

“…Recent work showed that expressing mer operon genes encoding for cysteine-containing mercuric ion transport proteins (such as periplasmic protein MerP or inner membrane protein MerT) [2,30,31] on Escherichia coli hosts could make them very effective biosorbents for heavy metals removal. In addition, several other metal-binding proteins, such as metallothioneins (MTs) [32,33], phytochelatins (PCs) [34], and metal-binding peptides [2] were also expressed on E. coli to create powerful biosorbents. Although MerP protein is a target for the development of genetically engineered biosorbents [35], there is little information on utilizing MerP-expressing biosorbents to remove heavy metals (especially for metals other than mercury) [2].…”