Team:Imperial College London/M3

• The aim of Module 3 is to remove all the genetic material after encapsulation has taken place.

A key design consideration when developing The E.ncapsulator was that the E. coli should be dead upon ingestion. This will prevent any transfer of genetic material between bacterium and host, and will also help to allay fears that people may have with regards to ingesting live bacteria.

However, a killing mechanism had to be designed whereby the bacterial membrane is left in tact so as not to disrupt the structure of the colanic acid layer. Any killing mechanism that completely destroys the bacterium would defeat the purpose of having a self-encapsulating drug production and delivery system. With this in mind, a strategy was devised that takes advantage of restriction enzymes DpnII and TaqI and the native E. coli dam methylase protection against these restriction enzymes. The dam methylation provides to protect the bacterium during drug production and encapsulation stages.

The killing mechanism is only to be triggered once encapsulation is complete. This caveat brings with it certain restrictions in terms of trigger mechanisms that could be adopted in our system; the presence of the colanic acid capsule means chemical or light triggers would not be as efficient as when the capsule is lacking. To overcome this, induction of genomic neutralisation by heat was decided upon.

The λcI gene inhibits the λcI promoter under which DpnII and TaqI are controlled. Upon increasing temperature to 37°C - 40°C the λcI gene undergoes a conformational change and is no longer able to bind the λcI promoter. The promoter is then free to transcribe DpnII and TaqI and cleavage of the E. coli genome is induced, rendering the bacterium no more than an inanimate shell containing our protein drug of choice.