Data from: The use of a mercury biosensor to evaluate the bioavailability of mercury-thiol complexes and mechanisms of mercury uptake in bacteria

As mercury (Hg) biosensors are sensitive to only intracellular Hg, they are useful in the investigation of Hg uptake mechanisms and the effects of speciation on Hg bioavailability to microbes. In this study, bacterial biosensors were used to evaluate the roles that several transporters such as the glutathione, cystine/cysteine, and Mer transporters play in the uptake of Hg from Hg-thiol complexes by comparing uptake rates in strains with functioning transport systems to strains where these transporters had been knocked out by deletion of key genes. The Hg uptake into the biosensors was quantified based on the intracellular conversion of inorganic mercury (Hg(II)) to elemental mercury (Hg(0)) by the enzyme MerA. It was found that uptake of Hg from Hg-cysteine (Hg(CYS)2) and Hg-glutathione (Hg(GSH)2) complexes occurred at the same rate as that of inorganic complexes of Hg(II) into Escherichia coli strains with and without intact Mer transport systems. However, higher rates of Hg uptake were observed in the strain with a functioning Mer transport system. These results demonstrate that thiol-bound Hg is bioavailable to E. coli and that this bioavailability is higher in Hg-resistant bacteria with a complete Mer system than in non-resistant strains. No difference in the uptake rate of Hg from Hg(GSH)2 was observed in E. coli strains with or without functioning glutathione transport systems. There was also no difference in uptake rates between a wildtype Bacillus subtilis strain with a functioning cystine/cysteine transport system, and a mutant strain where this transport system had been knocked out. These results cast doubt on the viability of the hypothesis that the entire Hg-thiol complex is taken up into the cell by a thiol transporter. It is more likely that the Hg in the Hg-thiol complex is transferred to a transport protein on the cell membrane and is subsequently internalized.

由于汞（mercury, Hg）生物传感器仅对细胞内的汞具有响应，因此可用于研究汞的摄取机制以及形态变化对微生物摄取汞的生物可利用性的影响。本研究采用细菌生物传感器，通过对比具有完整转运系统的菌株与通过敲除关键基因使上述转运系统失活的菌株的汞摄取速率，评估了谷胱甘肽、胱氨酸/半胱氨酸以及Mer转运蛋白等多种转运系统在汞-硫醇复合物摄取汞过程中所发挥的作用。生物传感器对汞的摄取量可通过酶MerA介导的无机汞（Hg(II)）向元素汞（Hg(0)）的细胞内转化过程进行定量分析。研究发现，无论大肠杆菌（Escherichia coli）菌株是否具有完整的Mer转运系统，从汞-半胱氨酸（Hg(CYS)₂）与汞-谷胱甘肽（Hg(GSH)₂）复合物中摄取汞的速率，均与Hg(II)无机复合物的摄取速率一致，但在具有完整Mer转运系统的菌株中，汞摄取速率显著更高。上述结果表明，大肠杆菌可利用结合硫醇的汞，且带有完整Mer系统的抗汞细菌对这类汞的生物可利用性高于非抗性菌株。在带有或缺失功能性谷胱甘肽转运系统的大肠杆菌菌株中，从Hg(GSH)₂中摄取汞的速率并无显著差异。带有功能性胱氨酸/半胱氨酸转运系统的野生型枯草芽孢杆菌（Bacillus subtilis）菌株与该转运系统被敲除的突变菌株之间，汞摄取速率同样无显著差异。上述结果对‘完整的汞-硫醇复合物可通过硫醇转运蛋白被细胞摄取’这一假说的可行性提出了质疑，更合理的推测是，汞-硫醇复合物中的汞会先转移至细胞膜上的转运蛋白，随后再被内化进入细胞。