(Here is an interesting cartoon we made, showing the general idea of our project.)
Atrazine is one of the most heavily used herbicides and it is used to control the growth of weeds. Atrazine is also a persistent environmental pollutant, it can cause problems like suppressing the growth of some other plants, inducing complete feminization and chemical castration in male frogs, and disrupting the human body's internal systems. Widespread contamination of groundwater has been reported in the United States. As such, there are increasing concerns over the toxicity of atazine in the environment [1, 2].
Considering the fact that atrazine can hardly be degraded naturally in soil and water, we designed and constructed a system in E.coli to make them move towards atrazine simultaneously and absorb it, degrade it into a harmless chemical substance.
For a start, to equip the bacteria with the ability to recognize atrazine, we utilized a smart ribosome switch to recognize the presence of atrazine. In the absence of atrazine, the secondary structure of the ribosome switch forms a pseudoknot, sequestering the ribosome-binding site. In this way, the expression of downstream genes is inhibited. However, in the presence of atrazine, the conformation of the switch changes, the ribosome-binding site is therefore exposed, so the genes downstream can be expressed [1].
When our bacteria can detect the presence of atrazine, we improved their performance by inserting quorum sensing (QS) system into the circuits. When they smell the signal of atrazine, they immediately send out acyl-homoserine lactone (AHL) signal to recruit more team members to gather around the atrazine pollution [3].
Once enough atrazine gather around the atrazine pollution, the density of bacteria pulls the trigger of Plsr, which starts to drive the expression of downstream genes, and the bacteria are therefore able to secrete the super degrading enzyme, TrzN.
However, the low transportation efficiency of atrazine from the outside to the inside of the bacteria posed a problem to us. Luckily, an amazing transporter TRM provided us with an answer. With HPLC, we surprisingly found that TRM can distinctively transport atrazine into our bacteria so the entire system can work more sensitively.
What’s more, in order to acquire a better performance, we modified some of our parts, such as TrzN and CI-tag, to make them function even better.
At the same time, we also used the computer calculation to simulate several systems, and we finally located on the best one which can make the bacteria move, gather and degrade faster.
For the last two months, we have completed some great achievements. A happy and united team was formed and we have successfully constructed 7 brilliant biobrick parts. To take a further step, we improved some parts’ functions with scientific modification. Our human practices spread the concept and notion of synthetic biology as well as our project to many advanced teenagers across the nation.
We know exactly that our work still has a long way to go to get near to industrialization and commercialization, but we do believe that this hope can be eventually realized. Just think about the fascinating progress from the first computer to the PC, iPad and iPhone today, our research perhaps is still lingering in the “old times”, but we have enough confidence that it will shock the world one day, providing us with a final answer to the pollution of atrazine.
Reference
[1] Sinha J, et al. Reprogramming bacteria to seek and destroy a herbicide. Nature chemical biology, 2010, 6 (6): 464-470.
[2] Hayes TB, et al. Atrazine induces complete feminization and chemical castration in male African clawed frogs (Xenopus laevis). Proceedings of the National Academy of Sciences, 2010, 107 (10): 4612-4617.
[3] Carter KK, et al. Pathway engineering via quorum sensing and sRNA riboregulators-Interconnected networks and controllers. Metabolic Engineering, 2012, 14 (3): 281-288.
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