Environ Sci Technol. 2015 Jan 20;49(2):990-8. doi: 10.1021/es505049f.
Bioavailability of trace metals is a key parameter for assessment of toxicity on living organisms. Proper evaluation of metal bioavailability requires monitoring the various interfacial processes that control metal partitioning dynamics at the biointerface, which includes metal transport from solution to cell membrane, adsorption at the biosurface, internalization, and possible excretion. In this work, a methodology is proposed to quantitatively describe the dynamics of Cd(II) uptake by Pseudomonas putida. The analysis is based on the kinetic measurement of Cd(II) depletion from bulk solution at various initial cell concentrations using electroanalytical probes. On the basis of a recent formalism on the dynamics of metal uptake by complex biointerphases, the cell concentration-dependent depletion time scales and plateau values reached by metal concentrations at long exposure times (>3 h) are successfully rationalized in terms of limiting metal uptake flux, rate of excretion, and metal affinity to internalization sites. The analysis shows the limits of approximate depletion models valid in the extremes of high and weak metal affinities. The contribution of conductive diffusion transfer of metals from the solution to the cell membrane in governing the rate of Cd(II) uptake is further discussed on the basis of estimated resistances for metal membrane transfer and extracellular mass transport.
金属的生物利用度是评估生物毒性的关键参数。要正确评估金属的生物利用度，需要监测控制生物界面金属分配动力学的各种界面过程，其中包括金属从溶液向细胞膜的传输、在生物表面的吸附、内化和可能的排泄。在这项工作中，提出了一种定量描述铜绿假单胞菌摄取 Cd(II)动力学的方法。该分析基于使用电化学探针在不同初始细胞浓度下从体相溶液中定量测定 Cd(II)耗竭的动力学测量。基于最近关于复杂生物界面金属摄取动力学的形式理论，根据限制金属摄取通量、排泄速率和金属与内化位点的亲和力，成功地解释了在长时间暴露 (>3 h) 后金属浓度的细胞浓度依赖性耗竭时间尺度和达到的平台值。该分析表明了在高金属亲和性和弱金属亲和性极端情况下近似耗竭模型的局限性。还根据估计的金属膜传递和细胞外质量传递的电阻，进一步讨论了从溶液到细胞膜的金属导电扩散传递对 Cd(II)摄取速率的控制作用。
