Expression of Arsenic Regulatory Protein in Escherichia coli for Selective Accumulation of Methylated Arsenic Species

ArsR is a metalloregulatory protein with high selectivity and affinity toward arsenic. We hereby report the expression of ArsR in Escherichia coli by cell engineering, which significantly enhances the adsorption/accumulation capacity of methylated arsenic species. The ArsR-expressed E. coli cells (denoted as E. coli-ArsR) give rise to 5.6-fold and 3.4-fold improvements on the adsorption/accumulation capacity for monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), with respect to native E. coli cells. The uptake of MMA and DMA by the E. coli-ArsR is a fast process fitting Langmuir adsorption model. It is interesting to note that the accumulation of methylated arsenic is virtually not affected by the presence of competing heavy-metal species, at least 10 times of Cd(II) and Pb(II) are tolerated for the adsorption of 1 mg L-1 methylated arsenic. In addition, an ionic strength of up to 2 g L-1 Na+ poses no obvious effect on the sorption of 1 mg L-1 MMA and DMA. Furthermore, the accumulation of MMA and DMA is less sensitive to the variation of pH value, with respect to the blank control cells. Consequently, 82.4% of MMA and 96.3% of DMA at a concentration Of 50 mu g L-1 could be readily removed from aqueous medium by 12 g of E. coli-ArsR. This illustrates a great potential for the E. coli-ArsR for selective remediation of methylated arsenic species in waters, even in the presence of a high concentration of salts.