Dissolved organic matter (DOM) strongly influences the geochemical mobility of metal ions, yet little is known about the mechanism of lead (Pb) binding to DOM in the presence of copper (Cu) and zinc (Zn). This research used different types of ultraviolet–visible (UV–vis) spectroscopy analysis technologies, including differential log-transformed spectra coupled with spectral slope calculation, and two-dimensional correlation spectroscopy (2D-COS) analysis to investigate the binding characteristics between Pb and DOM in the presence of Zn and Cu, respectively. The results indicate that the addition both of Zn 2+ or Cu 2+ can reduce the binding of DOM to Pb 2+ , with the effect of Cu 2+ being the most obvious. Specifically, significant changes were evident in the differential log-transformed absorbance at higher Zn 2+ /Cu 2+ concentrations, including modified spectral shapes, absorption wavelength fluctuation, and differential absorption intensity changes. The differential log-transformed absorbance spectral slopes (∆S 350-400 ) exhibited a positive correlation with the predicted NICA-Donnan model value in a wavelength range of 350–400 nm. This suggested that ∆S 350-400 served as an indicator for assessing the complexation characteristics of Pb and DOM binding in the presence of Zn 2+ and Cu 2+ , respectively. The 2D-COS spectral results showed that the presence of Zn 2+ /Cu 2+ changed the binding order of the DOM functional groups in response to Pb 2+ . This study revealed that Zn 2+ and Cu 2+ competed with Pb 2+ for complex sites on the DOM surface in different ways, altering the ability of Pb 2+ to bind with DOM. The results suggest that using differential log-transformed spectroscopy combined with ∆S 350-400 and 2D-COS analyses is a promising approach to understanding the mechanisms of Zn 2+ /Cu 2+ effects on Pb-DOM interactions, which may provide new insights into the prevention, control, and remediation of environmental Pb pollution.
Objectives To improve the Pb 2+ biosorption capacity of the potential E. coli biosorbent, a putative Pb 2+ binding domain (PbBD) derived from PbrR was efficiently displayed on to the E. coli cell surface. Results The PbBD was obtained by truncating the N-terminal DNA-binding domain and C-terminal redundant amino acid residues of the Pb 2+ -sensing transcriptional factor PbrR. Whole-cell sorbents were constructed with the full-length PbrR and PbBD of PbrR genetically engineered onto the surface of E. coli cells using Lpp-OmpA as the anchor. Followed by a 1.71-fold higher display of PbBD than PbrR, the presence of PbBD on the surface of E. coli cells enabled a 1.92-fold higher Pb 2+ biosorption than that found in PbrR-displayed cells. Specific Pb 2+ binding via PbBD was the same as Pb 2+ binding via the full-length PbrR, with no observable decline even in the presence of Zn 2+ and Cd 2+ . Conclusions Since surface-engineered E. coli cells with PbBD increased the Pb 2+ binding capacity and did not affect the adsorption selectivity, this suggests that surface display of the metal binding domain derived from MerR-like proteins may be used for the bioremediation of specific toxic heavy metals.
In vitro Lead (Pb 2+ ) binding capacity of two probiotic bacteria strains, namely Bifidobacterium longum BB79 and Lactobacillus pentosus ITA23, was assessed following incubation with the intestinal contents (IC) of laying hens. Results of this study demonstrated that IC treatment significantly enhanced ( P <0.01) Pb 2+ binding capacity of both bacterial strains. Fourier transform infrared analysis indicated that several functional groups (O-H or N-H, C-H, C˭O, C-O, and C-O-C) on the bacteria cell wall involved in metal ion binding were altered after IC incubation, and new groups appeared between the 3700 cm −1 and 4000 cm −1 bands. Transmission electron microscopy demonstrated that after incubation with IC, unidentified IC components created new binding sites on the bacterial cell surface. These particles also changed the mechanism of Pb 2+ binding of the two strains from intracellular accumulation to extracellular adsorption.
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