CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China.
CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China.
J Hazard Mater. 2021 Jun 15;412:125248. doi: 10.1016/j.jhazmat.2021.125248. Epub 2021 Jan 28.
Cadmium (Cd) is a typical and widely present toxic heavy metals in environments. Biomineralization of Cd ions could alleviate the toxicity and produce valuable products in certain waste streams containing selenite. However, the impact of the intrinsic Cd(II) efflux system on the biotransformation process remains unrevealed. In this work, the significance of the efflux system on Cd biomineralization was evaluated by constructing engineered Escherichia coli strains, including ΔzntA with suppressed Cd(II) efflux system and pYYDT-zntA with strengthened Cd(II) efflux system. Compared to the wild type (WT), 20% more Cd ions were accumulated in ΔzntA and 17% less were observed in pYYDT-zntA in the presence of selenite as determined by inductively coupled plasma atomic emission spectrometer. Through combination with X-ray absorption fine structure analysis, it was discovered that 50% higher production of CdSSe quantum dots (QDs) was achieved in the ΔzntA cells than that in the WT cells. Moreover, the ΔzntA cells exhibited the same viability as the WT cells and the pYYDT-zntA cells because accumulated Cd ions were transformed into biocompatible QDs. In addition, the biosynthesized QDs had a uniform particle size (3.82 ± 0.53 nm) and a long fluorescence lifetime (45.6 ns), which could potentially be utilized for bio-imaging. These results not only elucidate the significance of Cd(II) efflux system in the biotransformation of Cd ions and selenite, but also provide a promising way to recover Cd and Se as valuable products in certain waste streams.
镉（Cd）是环境中典型且广泛存在的有毒重金属之一。在含有亚硒酸盐的某些废物流中，Cd 离子的生物矿化可以减轻其毒性并产生有价值的产物。然而，内源性 Cd（II）外排系统对生物转化过程的影响仍未被揭示。在这项工作中，通过构建工程大肠杆菌菌株，包括抑制 Cd（II）外排系统的 ΔzntA 和增强 Cd（II）外排系统的 pYYDT-zntA，评估了外排系统对 Cd 生物矿化的重要性。与野生型（WT）相比，在存在亚硒酸盐的情况下，ΔzntA 中积累了 20%的更多 Cd 离子，而 pYYDT-zntA 中则观察到 17%的更少 Cd 离子，这是通过电感耦合等离子体原子发射光谱仪确定的。通过与 X 射线吸收精细结构分析相结合，发现 ΔzntA 细胞中 CdSSe 量子点（QDs）的产量比 WT 细胞高 50%。此外，由于积累的 Cd 离子被转化为生物相容性的 QDs，ΔzntA 细胞与 WT 细胞和 pYYDT-zntA 细胞具有相同的活力。此外，生物合成的 QDs 具有均匀的粒径（3.82±0.53nm）和长荧光寿命（45.6ns），可用于生物成像。这些结果不仅阐明了 Cd（II）外排系统在 Cd 离子和亚硒酸盐生物转化中的重要性，而且为在某些废物流中以有价值的产品回收 Cd 和 Se 提供了一种有前途的方法。
