Equilibrium, kinetic, and thermodynamic studies on the biosorption of lead by human metallothionein gene-cloned bacteria as a novel biosorbent.

Abstract

Heavy metals are the main pollutants in water and are an important global problem that threatens human health and ecosystems. In recent years, there has been an increasing interest in the use of genetically modified bacteria as an eco-friendly method to solve heavy metal pollution problems. The goal of this study was to generate genetically modified Escherichia coli expressing human metallothioneins (hMT2A and hMT3) and to determine their tolerance, bioaccumulation, and biosorption capacity to lead (Pb2+ ). Recombinant MT2A and MT3 strains expressing MT were successfully generated. Minimum inhibition concentrations (MIC) of Pb for MT2A and MT3 were found to be 1750 and 2000 mg L-1 , respectively. Pb2+ resistance and bioaccumulation capacity of MT3 were higher than MT2A. Therefore, only MT3 biosorbent was used in Pb2+ biosorption, and its efficiency was examined by performing experiments in a batch system. Pb2+ biosorption by MT3 was evaluated in terms of isotherms, kinetics, and thermodynamics. The results showed that Pb biosorption fits to the Langmuir isotherm model and the pseudo-first-order kinetic model, and the reaction is exothermic. The maximum Pb2+ capacity of the biosorbent was 50 mg Pb2+ g-1 . The potential of MT3 in Pb biosorption was characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM) analyses. The desorption study showed that the sorbent had up to 74% recovery and could be effectively used four times. These findings imply that this biosorbent can be applied as a promising, precise, and effective means of removing Pb2+ from contaminated waters. PRACTITIONER POINTS: In this study, the tolerance levels, bioaccumulation, and biosorption capacities of Pb in aqueous solutions were determined for the first time in recombinant MT2A and MT3 strains in which human MT2A and MT3 genes were cloned. The biosorbent of MT3, which was determined to be more effective in Pb bioaccumulation, was synthesized and used in Pb biosorption. The Pb biosorption mechanism of MT3 biosorbent was identified using isotherm modeling, kinetic modeling, and thermodynamic studies. The maximum Pb removal percentage capacity of the biosorbent was 90%, whereas the maximum biosorption capacity was up to 50 mg Pb2+ g-1 . These results indicated that MT3 biosorbent has a higher Pb biosorption capacity than existing recombinant biosorbents. MT3 biosorbent can be used as a promising and effective biosorbent for removing Pb from wastewater.