J Environ Qual. 2019 Jan;48(1):199-204. doi: 10.2134/jeq2018.10.0352.
Whole-cell bacterial biosensors (bioreporters) are commonly applied for determination of metal toxicity and bioavailability in environmental samples. This is accomplished using a standard procedure whereby the sample is mixed with bioreporter cells suspended in a buffered medium at a fixed pH (set-point pH assay). This experimental approach can alter the sample pH. We therefore hypothesized that metal speciation artifacts compromising our ability to use bioreporters for determination of the "true" metal bioavailability in environmental samples may be introduced. Using the copper-specific bioreporter DF57-Cu15 as a model, we compared the conventional set-point pH assay to a flexible pH assay allowing for bioavailability determination at in situ sample pH. Our results demonstrate that pH-dependent metal speciation bias may occur when using the conventional set-point pH assay, and we recommend performing bioreporter measurements and calibrations at in situ sample pH. Although we only studied copper bioavailability, our results also have implications for bioreporter determination of other analytes displaying pH-dependent speciation such as other metals and some organics. We call for additional bioreporter studies of chemical speciation artifacts as this represents a problem hitherto overlooked in bioreporter literature. We thus conclude that there may be considerable scope for optimization of existing bioreporter assays for assessment of environmental pollutant bioavailability.
全细胞细菌生物传感器（生物报告器）常用于测定环境样品中的金属毒性和生物可利用性。这是通过使用标准程序来完成的，其中将样品与悬浮在缓冲介质中的生物报告器细胞混合，在固定 pH 值（设定点 pH 测定）下进行。这种实验方法可能会改变样品的 pH 值。因此，我们假设可能会引入金属形态分析物的假象，从而影响我们使用生物报告器来测定环境样品中“真实”金属生物利用度的能力。我们使用铜特异性生物报告器 DF57-Cu15 作为模型进行研究，将传统的设定点 pH 测定法与允许在原位样品 pH 下进行生物利用度测定的灵活 pH 测定法进行了比较。我们的研究结果表明，当使用传统的设定点 pH 测定法时，可能会发生 pH 依赖性金属形态分析物的偏析，因此我们建议在原位样品 pH 下进行生物报告器测量和校准。虽然我们仅研究了铜的生物利用度，但我们的结果也对其他显示 pH 依赖性形态的生物报告器分析物（如其他金属和一些有机物）的测定具有启示意义。我们呼吁对化学形态分析物的假象进行更多的生物报告器研究，因为这是生物报告器文献中迄今被忽视的问题。因此，我们得出结论，对于评估环境污染物生物利用度的现有生物报告器测定法进行优化可能具有很大的潜力。
