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Team:Edinburgh/Artificial Selection
From 2011.igem.org
Suppose, like most people, you want to create E. coli that is really efficient at degrading cellulose. Rather than do a bunch of difficult genetic engineering work, why not let Darwin do the work for you? If you simply get your E. coli working at 1% efficiency, can't you just use artificial selection to get you the remaining 99% of the way?
If cellulose is the only food source available for your culture, this strategy should work. But there's a problem: if your E. coli simply secrete cellulases into the media, then a rare mutant that produces more or better cellulases will not gain much benefit, since these cellulases float away and will probably benefit other cells instead.
However, if the cellulases are attached to the cell (for example, because they are part of a fusion to Ice Nucleation Protein...) then this problem does not arise; the rare mutant gains all of the benefit, since the sugar that is created is right there beside it.
To demonstrate this, enter Team Synergy's Celluvolve computer simulation!
The rules are as follows:
- An array of bacteria exists.
- Each bacterium has a "genotype": its ability to produce cellulase.
- The genotype is a number between 0 and 255.
- Each iteration, some random bacteria are chosen.
- These bacteria have a chance to reproduce, based on their food supply.
- Food supply is defined either as:
- (LEFT) The ability of the cell to produce cellulase.
- (RIGHT) The average ability of nearby cells (including itself).
- Reproduction means:
- Overwriting a randomly chosen cell with one's own genotype.
- However, reproduction is not exact. There is "mutation".
- The offspring's genotype is a number close to the parent's.
The left half of the simulation models the case where the cellulase produced by a cell can only benefit itself. The right half models the case where the cellulase can float away and benefit neighbours instead of the cell that produced it.
Software
The program can be downloaded at File:Celluvolve.zip. It requires [http://www.libsdl.org/ Simple DirectMedia Layer] (SDL) 1.2 to work. In Ubuntu, try downloading libsdl1.2-dev using the Package Manager.
Simulation run
In this simulation, each pixel represents a bacterium. Its brightness indicates its ability to produce cellulase. In the left half of the simulation, the cellulase benefits only the producer, whereas in the right half, it floats a small distance and so also benefits 4 of the producer's neighbours.
Graph
