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Future Directions

Though the iGEM 2012 is coming to an end,we plan to do further research to make our research accomplished and endue it with new functions. In the future, with enough time and abundant knowledge, these meaningful designs will be realized.

1.Plasmid Keeping System

Mechanism of the hok/sok system in bacteria in the presence of R1 plasmid DNA
Mechanism of the hok/sok system in bacteria in the absence of R1 plasmid DNA

We plan to construct a plasmid keeping system to avoid plasmid loss. In phage-free situations, the bacteria is likely to lose the anti-phage plasmid, therefore a plasmid keeping system is necessary. We choose the hok/sok system to achieve this. It belongs to type I toxin-antitoxin system. The cell will die if the cell lost the plasmid containing the system. Thus, only those cells contain survives. Besides, the type I toxin-antitoxin system is an RNA based system, therefore it won't spend too much energy.

2.Quorum Sensing

Structure of sugar translocation, also called LamB, the receptor site for lambda phage
Ideal function of the aptamer in our future work
Ideal function of the aptamer in our future work

Actually, in the primary plan of our project, our design was that when the suicide gene works, the host would use quorum sensing to alarm the bacteria around and make them prepare for the defense. We don't hope the bacteria spend a lot of energy on the defense when no phage invades. To this end, we design that the defense action will be taken only when the bacteria receive the quorum sensing signal, which is sent by the host. The reason for giving up this feature is that we haven't found any effective defense method. The defense method in our plan was blocking the phage’s binding site on the membrane of bacteria. We learned that a sugar transporter called LamB (the structure is showed below) may be the phage’s binding site and we planned to use aptamer to block this site.

Proposed model for the folding of LamB in the outer membrane.
Proposed model for the folding of LamB in the outer membrane.

But unfortunately, there are too many difficulties we have to face. For example, we haven't find a method to make the aptamer get through the inner membrane of E.coli. What’s more, LamB is so complex that it will be quite difficult for us to get an aptamer that works.(see the proposed model for the folding of LamB in the outer membrane.).

Therefore in the future,we will raise some new ideas complete the quorum sensing part.

3.Application To Fermentation Industry

We plan to apply this method to other fermentation industries. In general, our circuit in the engineered bacteria will work if we replace the promoter pRM with a specific one. We will also select a suicide gene which is biocompatible with the target and can also promote the quorum sensing.

4.Cure For Viral Diseases

If possible, we will make some medical research with this method, because this anti-virus method is universal. It will be a possible way on therapies against viral diseases, such as the HIV and the Flu.