Fig. 2

The heavy metal sensing mechanism of genetically engineered bacterial cells. The lacUV5 promoter controls the T7 RNA polymerase gene in the E. coli-BL21 genome. The Lac repressor binds to the Lac operator, repressing its activity. Upon the addition of IPTG inducer, the Lac repressor dissociates from the Lac operator. Subsequently, T7 polymerase is synthesized by the E. coli genome. This leads to the expression of the CadR gene by T7 polymerase, and the CadR protein binds to the PcadA operator, resulting in the repression of eGFP expression. In the presence of Cd²⁺ ions (green capsular symbol), the CadR protein undergoes a conformational change due to Cd²⁺ ion binding, causing its dissociation from the PcadA operator. This complete process allows for the expression of eGFP protein specifically in the presence of the corresponding metal ions, such as Cd²⁺ (illustrated by Cd.²⁺)