Mercury resistance and accumulation in Escherichia coli with cell surface expression of fish metallothionein

Abstract

Recombinant tilapia (Oreochromis mossambicus) fish metallothionein (MT) was used as a surface biosorbent for mercury removal in Escherichia coli. Fish MT conferred better resistance than did mouse or human MT. When tilapia MT (tMT) was fused with an outer-membrane protein, outer membrane protein C (OmpC), the membrane-targeted fusion protein, OmpC-tMT, gave enhanced resistance compared with cytoplasmic tMT expressed in the same host cell. The cytoplasmically expressed tMT showed high mercury adsorption (4.3 +/- 0.4 mg/g cell dry weight). The cell surface that expressed E. coli showed about 25% higher adsorption ability (5.6 +/- 0.4 mg/g) than the cells expressing cytoplasmic MT, attaining almost twice the level of adsorption of the control plasmid (3.0 +/- 0.4 mg/g). As MTs are also known for their ability to scavenge hydroxyl-free radicals, it was also shown that tMT exhibited better radical-scavenging activities than glutathione. These results suggest that fish MT has potential for the development of a bioremediation system for mercury removal that protects the harboring E. coli host by free-radical scavenging.

Improvement of n-butanol tolerance in Escherichia coliby membrane-targeted tilapia metallothionein

“…This could also be explained by its osmoregulation ability. Interestingly, the tolerances of MMT performed better than TMT in furfural (Figure 4a), Our previous studies [26], we found MT display different scavenging capacity between two kinds of radicals (ABTS ●+ and DPPH ● ). We suggested that MMT prefers to scavenge the type of ROS generated from furfural.…”

“…In this study, it was hypothesized that the increased alcohol tolerance in engineered E. coli strains was due to the ability of MTs, particularly the TMT strains, to possess higher scavenging efficiencies as previously reported [26]. Overall, both membrane-targeted MMT and TMT strains were found contributing to 3 times n- butanol (0.5% to 1.5%) and 1.25 times ethanol (4% to 5%) greater tolerances, respectively, than the control E. coli strains (pET30a).…”

“…For example, the tilapia fish ( Oreochromis mossambicus ), which serves as a biomarker for the contamination level of aqueous environments, has the ability to survive in a highly polluted environment because of its MTs function [24,25]. Furthermore, purified tilapia MT (TMT) has been shown to have a higher ability than glutathione (GSH) to scavenge both 2-diphenyil-1-picrylhydrazyl (DPPH ● ) and 2,2-azinobis (3-ethylbenzothiazoline- 6-sulfonic acid) diammonium salt (ABTS ●+ ) [26]. These observations have prompted us to postulate that TMT may serve as a good candidate for the purposes of metal absorption and free radicals scavenging in microorganisms during bio-fuel production.…”

A glutathione S-transferase from Proteus mirabilis involved in heavy metal resistance and its potential application in removal of Hg2+

“…Its adsorption efficiency was 7-fold higher than the control Top10/pBAT1, with 100% of Hg 2+ ranging from 0.1 to 100 nM adsorbed. This adsorption efficiency was higher than the genetically engineered bacteria E. coli strains overexpressed a single membrane component from a Bacillus mer operon (BMerP) and a tilapia metallothionein (tMT), which showed 27 and 25% increase in Hg 2+ adsorption efficiency [47,48]. Since no cysteine presented in the amino acid sequence, Gst Pm -4 may adsorb Hg 2+ via several charged surface functional groups like carboxyl, amino, carbonyl and hydroxyl that could interact with Hg 2+ through ion exchange and complex formation [42,49].…”

A Synthetic Circuit for Mercury Bioremediation Using Self-Assembling Functional Amyloids

“…10 However, it was found that the addition of a Hg 2+ transport system, encoded by the merT and merP genes, were essential for mercury sequestration. An alternative strategy uses cell-surface displayed mercury-binding proteins, such as a metallothioneins, 11 phytochelatins, 12 or the MerR metal binding domain, 13 to create engineered cellular biosorbents. These examples of engineered bacterial circuits for sensing and absorption of mercury demonstrate the exciting potential of green biological strategies for mercury remediation of contaminated environments.…”