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Revision as of 09:52, 4 August 2005

Intro & principle

A predator-prey behavior should be mimicked by two similar (but not identical) bacterial populations which will "hunt" each other periodically. This will be visually detectable as an obscillating change in fluorescence from green to red, like a sort of traffic light...

Approach

The two populations will be periodically exchanging the roles of predator and prey , by mutually activating a toxic gene. Timing should be controlled by concentration levels of inducers and, obviously, of the toxin.

The features

Population Red:

• constitutively expresses RFP.
• gene A: coding for quorum sensing factor A (e.g. AHL). Expression induced through external stimulus + auto-induction.
• gene toxR: encoding a toxic protein (ccdB?). Expression induced by C.
• gene C: coding for transcriptional activator C. Expression indirectly induced by B (activates phosphorelay).

Population Green:

• constitutively expresses GFP.
• gene B: encoding transcriptional activator B, constitutively expressed.
• gene toxG: encoding a toxic protein (ccdB?). Expression induced by a threshold concentration of A.

The idea

The predator-prey behavior will be elicited by an external stimulus (e.g. IPTG or wathever), which will activate the transcription of the quorum sensing factor A in the red population. As soon as a threshold concentration of A is achieved, this will trigger transcription of a toxG gene in the green population. The tox gene encodes for a toxin,which will kill green cells to some extent (they should not all be killed). Moreover, the green population was constitutively expressing B, which can not cross the membrane unless the cells are dead... Therefore, death of green cells will lead to the release of B, and a threshold concentration of B will activate expression of C in the red population, which in turn will induce transcription of the toxR gene. Then will cell density of the red population decrease, and a lower concentration of A will be present, so that the green survivors can begin to re-grow, etc etc etc etc etc etc.

The ???????

• Quite complicated, will it possibliy work???
• Which toxin can be used to lower the population OD/cell count without killing the whole pop? Could CcdB be useful for this task?
• Will populations actually oscillate? Or will they soon reach a steady state?
• Literature shows that, after a while, prey population acquire resistance to the predator. Would that be possible in this case? Since populations are both prey and predator, would this plastic adaptation end up in a "draw"?
• Will bistability be a problem?

Discussion

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