Module 6: Containment

Description | Design | Construction | Characterisation | Modelling | Results | Conclusions

Design

We have identified a single key requirement for the design of the Containment Module.

Requirement: The system must be able to effectively counter horizontal gene transfer, preventing our cells from being able to transfer their genes into wild strains of cells.

Horizontal gene transfer can occur in several ways:

(i) Bacterial conjugation - where DNA is transferred between microbes via cell-to-cell contact.

(ii) Transduction - where bacterial DNA is transferred between cells via a viral vector.

(iii) Transformation - where DNA in the environment uptakes into the cell.

In our examination of the literature, we have identified several systems that could be utilised to prevent horizontal gene transfer. A dual containment system, comprising Colicin E3, and EcoRI restriction endonuclease has been identified to be ideal for our purposes. From the literature (Torres et al. 2003), it has been determined that multi-containment systems are more effective than mono-containment systems, and as such, we have decided to do the same. Furthermore, as the expression of suicide genes may be variable in different microbial strains, multi-containment systems would significantly reduce the effects of horizontal gene transfer.

As the multi-containment system is an effective guard against bacterial conjugation, but not necessary against transformation, we have decided to incorporate an exonuclease into our containment system as well. Any DNA released due to cell lysis would be degraded by the exonuclease.

Due to the constrains of our project, we are unable to implement a system that would directly target transduction. As transduction has been suggested to be a key mechanism for horizontal gene transfer in the marine environment (Jiang et al. 1998), this would be an area that we would wish to investigate further in the future.