From 2007.igem.org

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Self-differentiated Bacterial Assembly Line

Our projects concerns with the ability for bacterial cells to differentiate out of homogeneous conditions to achieve the division of labor. We want to design devices conferring host cells with the ability to spontaneously form cooperating groups and to take consecutive step even when the genetic background and environmental inputs are identical. To break the mirror in such homogeneous condition, we need two devices respectively responsible for temporal and spatial differentiation. The implementation and application of such devices will lead to a picture of future bioengineering where complex programs consisted of sequential steps (structure oriented programs) and cooperating agencies (forked instances of a single class, object and event oriented) can be embedded in a single genome. The expression of such a genome pre-programmed both temporally and spatially both resembles the differentiation process of multicellular organism and a assembly plant built out of a blueprint.

Hop Count with Conjugation

Hop counting is a cell-cell communication system in which the signals transfered among the cells record the number of times of transfer. we have adapted natural conjugation systems as the communication device, and the conjugative plasmids as the vector for the transfered signal. Concerning the special feature of the rolling-cycle replication of DNA during conjugation, we plan to insert independent tandem oriT (BBa_J01002 and more) pairs into the same plasmids, which lost one tandem region at one single conjugation event, thus record the number of conjugation on the presence/absence of regions on the plasmid of arbitrary length . Sequential conjugation and deletion of the different oriT pairs can be achieved by fine control of the expression of the cis-acting elements of the independent conjugation systems. In fact, we inserted the relaxases responsible for the initiation of conjugative DNA replication between the corresponding oriTs, rendering the independent conjugative systems functioning at specified order.

Push-on-push-off Switch

Push-on-push-off switches are binary switches flipping to different direction under the same impulses, depending on the previous states it resides. It differed from a toggle switch that the forces flip the switch back and force are exactly the same. We have designed a gene regulatory circuit that senses Ultra-Violet light (UV) irradiation as input signal. Under intermittent irradiation, two reporter genes are to be induced alternately. The circuit can be divided into two associated parts: a bistable switch and a NOR gate. The bistable switch resembles a toggle switch where the NOR gate is controlled by the bistable switch and the input signal. On the other hand, the output of the NOR gate can switch the bistable state from one to the other. Thus far, we have constructed and tested a series of NOR gates and one bistable switch, successfully obtaining the desired dynamics for our function.