Biosafety System AraCtive

Overview

Figure 1: Principle of electron transfer from bacteria to anode via nanowires.

The tetracyclin repressor (TetR)/ operator (TetO) originally is used by E. coli to work against the antibiotic tetracycline but in many cases it is used for regulated expression for industrial processes. When there is no tetracycline available the TetR binds with high affinity the tetracycline operator. When tetracycline is available the TetR switches his conformation and so it comes to a dissolution of the TetR and the TetO. Because of this the polymerase isn’t enhanced anymore and is able to express the genes which lies behind the TetO. In our system the TetR is under the control of a rhamnose promotor (rha-promotor) which only works in the presence of rhamnose. When the bacteria would break out of the MFC there wouldn’t be enough rhamnose in the environment to activate the promotor in a way that enough TetR would be produced to block the polymerase by binding at the TetO. Therefore the polymerase binds to the promotor of TetO and it comes to the expression of RNase Ba and the degradation of the DNA.

Genetic Approach

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.

Alanine Racemase

The alanine-racemase alr (EC 5.1.1.1) from the gram-negative enteric bacteria Escherichia coli is a racemase, which catalyses the reversible reaction from L-alanine into the enantiomer D-alanine. For this reaction the cofactor pyridoxal-5'-phosphate (PLP) is typically needed. The constitutive alanine-racemase (alr) is naturally responsible for the accumulation of D-Alanin, which is an essential component of the bacterial cell wall, because it is used for the crosslinkage of the peptidoglykan. The use of D-Alanin instead of a typically L-amino acids prevents the cleavage by peptdidases, but a lack of D-Alanin leeds to a bacteristatic characteristic. So in the absence of D‑Alanine dividing cells will lyse rapidly. So if the expression of the Alanin-Racemase is repressed and there is no D-Alanine-Supplementation in the media, the cells would not increase.

Figure x: The alanine-racemase from E. coli catalyses the reversible reaction from L-alanine to D-alanine.

Results

References

• Autoren (Jahr) Titel [Link|Paper Ausgabe: Seiten].