SUNDAY, 21 MAY 2006The competition involved 13 universities from around the globe. The challenge was to engineer living bacteria that could perform a specific task. Each team was given a ‘toolkit’ of standard, interchangeable parts called ‘BioBricks’. Each BioBrick is a DNA sequence with a known function; the DNA may code for genes or regulatory components (for example gene promoters). The teams were to design a simple biological system using BioBrick components and then implement their design in the laboratory using genetic engineering techniques. Tried and tested BioBricks are maintained in an online Registry of Standard Biological Parts (http://parts.mit.edu), a kind of virtual Lego box.
To construct a bacterial temperature sensor, you can simply order the appropriate components from the Registry and put them together in a bacterial cell. Each BioBrick DNA sequence is flanked by four sites at which specific restriction enzymes can cut. This means that by following a series of simple laboratory protocols, BioBricks can be assembled together on a plasmid (a circular piece of DNA that can replicate independently of the bacterial chromosome) and this can then be transformed into a bacterial cell to test the BioBricks for functionality. Our team decided to explore the feasibility of controlling the movement of bacterial cells (we used Escherichia coli as our model system).
We began by looking at the sugar maltose, which is both an energy source and a chemoattractant (certain bacterial strains are attracted to maltose, and will actively move towards areas where it is in high concentration). Thus, we hoped that by controlling the cell’s response to maltose, we could control the movement of E. coli towards maltose. To exert a degree of control over the movement of E. coli cells via a natural pathway,we needed to be able to establish on and off switches for chemotaxis (the directed motion of an organism toward favourable environmental conditions, and away from those deemed unfavourable). We achieved this by adapting a ‘genetic switch’ to control the expression of the bacterial gene malE, which encodes the sequence information for Maltose Binding Protein (MBP). MBP is required for the detection of maltose and is essential for directed movement towards the sugar.
To switch on MBP production we used a genetic switch, which utilised DNA recombination, that enabled the malE gene to be expressed in response to a specific chemical stimulus—isopropylbeta- D-thiogalactopyranoside (IPTG). Designing the ‘off’ switch for chemotaxis proved to be more difficult, as MBP takes a long time to degrade once it has been produced. This means that after removal of the chemical stimulus (IPTG), MBP is still present and able to detect maltose. Following further investigation, we discovered a malE mutant that produced an unstable form of MBP that disappears within 45 minutes (a relatively short time period in terms of protein lifespan). Incorporating the malE mutant will be the next stage of the project. Our complete genetic circuit is shown in the box below (where some of the detail behind the circuit is also explained). The ‘wet lab’ phase of the project was a great experience for us all, especially the engineers who had never even used a pipette before. Unfortunately the end of the summer came all too soon, and we had to travel to Cambridge, Massachusetts to present our work at the Massachusetts Institute of Technology.
All the competing teams congregated to present their projects in front of some of the biggest names in the field. It was truly amazing to see what each team, mostly or solely comprised of undergraduates, could develop in such a short time, with the quality of the work often rivalling that seen in published journals. After the presentations came the awards ceremony. The Cambridge team walked away with some of the most valued awards, including ‘Most Effective Approach’,‘Best Data and Data Visuals’ and, last but not least, the ‘Best Uniform’ award! www.plantsci.cam.ac.uk/Haseloff/iGEM2005
James Godman is a third year Natural Scientist specializing in Plant Sciences; Alice Young is a third year Natural Scientist specializing in Zoology; James Brown is a fourth year Engineer