System S in the MFC: In this case the mikroorganism is in the MFC with sufficient L-rhamnose. It comes to an expression of araC which blocks the arabinose-promoter by binding and alr which switches L-alanine to D-alanine. Because of the fact that araC blocks the arabinose-promoter the RNase Ba can't expressed.
System S outside of the MFC: In this case the mikroorganism could get out of the MFC by damage or incorrect handling. Outside of the MFC there isn't enough L-rhamnose. So araC doesn't block the arabinose-promotor any more and RNase Ba can be expressed.E.coli dies.
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