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From 2012.igem.org

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Through our project, we aim to design a stable community of microorganisms which interact according to our intentions and that could be used as a standard tool in lab and industry for different purposes. Hence our main biobrick is the actual organism!

In other words, our objective is to create a system that allows the co-culture of several genetically engineered machines in defined and tunable proportions in synthetic conditions, just like different species coexist in an ecosystem in nature. In order to do this we´ve come up with several plausible circuit designs, each of them that uses a different approach to the same issue and we´ll test the easiest one in order to prove it can work.

As a starting point, we will use two auxotrophic strains, one for tryptophan and other for histidine and we will tune the amount of these aminoacids that they export so that one cannot live without the other and they regulate each other´s growth.

Therefore the system is also tunable by a externally controlled variable as it is the concentration of aminoacids, such that the A:B proportion has a defined response curve with respect to the concentration of it. The culture should reach a plateau because of the action of a built-in regulatory system, as opposed to the depletion of nutrients and accumulation of toxic waste products. The proportion of the strains should be robust against external perturbations and stochastic fluctuations, given that there is a reciprocal regulation that acts like a moderator of changes in populations parameters.

This system should control the overall optical density (OD) of the culture at levels below saturation and we´ve run several in silico simulations prior to the actual experiments in order to assess the correct concentration and starting proportion needed for the success of our project. In the philosophy of the synthetic biology field, we would like to create re-utilizable and well-characterized parts and modules. In the future this would allow for other modules to control the proportions of each strain, thus allowing dynamic and stimulus dependent changes in the abundances of each strain.

Some possible applications (from the most classic to the wildest!)

• Circuit Integration: The possibility to co-culture several strains with different circuits can be used to increase the complexity and amount of components of the overall system. Currently there seems to be an upper limit to the amount of components a device can have. Combining several strains to achieve a function can be a way to overcome this limitation and introduce a new layer of modularity and control.

• Circuit Isolation: Dividing a big circuit in two or more strains can allow to build sub-circuits that would be otherwise incompatible in the same cell. This can allow more complex designs with fewer parts, as these can be used for different functions in different strains.

• Optimization of Bioreactor Output: If the steps of a complex reaction are carried out by different strains, the overall throughput of the process can be optimized by fine-tuning the proportion of each strain. Our system would allow to easily modify these proportions.

• Synthetic Oenology: The ability to use several yeast strains in defined proportions in a fermentation process can allow new varieties of wines with unique properties to be created. This can be of interest to the local wine industry.