Rare earth elements, especially how to capture them, have attracted numerous scholars to explore. They have successfully developed some functional sensors for some rare earth elements. However, the lanthanide elements, one of the important and wealthy rare earth elements, are not included, so our team plans to follow some researches in this field.
We have designed an intelligent system, which would not react unless the concentration of lanthanide ions reaches the threshold.
To reach our goal, we need a smart sensing circuit. Fortunately, we found a two-component system called PmrA/PmrB aimed at detecting iron ions. If we can find some appropriate sequences encoding particular proteins to adsorb lanthanide ions, we can replace the iron-binding sequence with them to achieve our goal.
Consulting a great amount of literature, we made it! And we learned that the most efficient lanthanide binder is lanthanide-binding tag, abbreviated as LBT. After we change the iron binding site to LBT, the sensing system would work as the followings: when a lanthanide ion bind to PmrB(LBT), PmrA would be phosphorylated. Then the phosphorylated PmrA will activate promoter PmrC. After that, GFP will be expressed, reporting the concentration of lanthanide ions nearby.
Ions sensing is just the first step, then we need to capture them. In this part, we also use LBT——our good lanthanide hunter.
In order to capture Tb3+ more efficiently, we connect 3 LBTs by GS linker on the membrane.
Now our bacteria have captured a lot of lanthanide ions. What we need to do at last is just collecting our cells. So we designed the Si-tag, which enables the bacteria to combine with silica net, so that we can recycle the cells to ensure the safety.
The circuit below can illustrate our project better:
