Abstract：
Various genetically engineered microorganisms have been developed for the removal of heavy metal contaminants. Metal biosorption by whole-cell biosorbents can be enhanced by overproduction of metal-binding proteins/peptides in the cytoplasm or on the cell surface. However, few studies have compared the biosorption capacity of whole cells expressing intracellular or surface-displayed metal-adsorbing proteins. In this study, several constructs were prepared for expressing intracellular and surface-displayed Ochrobactrum tritici 5bvl1 ChrB in Escherichia coli BL21(DE3) cells. E. coli cells expressing surface-displayed ChrB removed more Cr(VI) from aqueous solutions than cells with cytoplasmic ChrB under the same conditions. However, intracellular ChrB was less susceptible to variation in extracellular conditions (pH and ionic strength), and more effectively removed Cr(VI) from industrial wastewater than the surface-displayed ChrB at low pH (<3). An adsorptiondesorption experiment demonstrated that compared with intracellular accumulation, cell-surface adsorption is reversible, which allows easy desorption of the adsorbed metal ions and regeneration of the bioadsorbent. In addition, an intrinsic ChrB protein fluorescence assay suggested that pH and salinity may influence the Cr(VI) adsorption capacity of ChrB-expressing E. coli cells by modulating the ChrB protein conformation. Although the characteristics of ChrB may not be universal for all metal-binding proteins, our study provides new insights into different engineering strategies for whole-cell biosorbents for removing heavy metals from industrial effluents.
摘要：
已经开发了各种基因工程微生物来去除重金属污染物。全细胞生物吸附剂的金属生物吸附可以通过在细胞质中或细胞表面上过度产生金属结合蛋白/肽来增强。然而,很少有研究比较表达细胞内或表面展示的金属吸附蛋白的全细胞的生物吸附能力。在这项研究中,制备了几种构建体，用于在大肠杆菌BL21（DE3）细胞中表达细胞内和表面展示的黑嗜血杆菌5bvl1ChrB。在相同条件下,表达表面展示的ChrB的大肠杆菌细胞比具有细胞质ChrB的细胞从水溶液中去除更多的Cr(VI)。然而,细胞内ChrB不易受细胞外条件（pH和离子强度）变化的影响，在低pH（<3）下，比表面显示的ChrB更有效地从工业废水中去除Cr（VI）。吸附解吸实验表明，与细胞内积累相比，细胞表面吸附是可逆的，这使得吸附的金属离子容易解吸和生物吸附剂的再生。此外,固有的ChrB蛋白荧光实验表明，pH和盐度可能通过调节ChrB蛋白构象来影响表达ChrB的大肠杆菌细胞的Cr（VI）吸附能力。尽管ChrB的特征可能并不适用于所有金属结合蛋白，我们的研究为全细胞生物吸附剂从工业废水中去除重金属的不同工程策略提供了新的见解。
