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. 2022 Apr 13;13:846524. doi: 10.3389/fmicb.2022.846524

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Copyright © 2022 Hui, Guo, Li, Chen and Yi.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Genetic organization of dual-sensing biosensor for detecting bioavailable Hg(II) and Cd(II). (A) Schematic representation of plasmid constructs used in the study. Two kinds of fluorescent reporter modules were placed under the control of Hg(II) sensory element or Cd(II) sensory element to assemble various single-sensing constructs. The Cd(II) biosensing system and the Hg(II) biosensing system were integrated into one genetic construct in two different directions. The DNA sequence and biological annotation of inserted fragments are shown in Supplementary Figure 1. (B) Molecular mechanisms of fluorometric determination of bioavailable cadmium and mercury. Dimeric metalloregulator CadR bound to the divergent cad promoter activates expression of the red fluorescence protein mCherry in the presence of Cd(II), and dimeric metalloregulator MerR acts as a transcription repressor without Hg(II) exposure (schematic in red box). Dimeric metalloregulator MerR bound to the divergent mer promoter activates production of the green fluorescence protein eGFP in the presence of Hg(II) (schematic in green box). When Cd(II) and Hg(II) appear in the cytoplasm simultaneously, the dual-sensing biosensor can differentially detect Cd(II) and Hg(II) with double-color fluorescence output (overlap between the red and green boxes).