Information processing subsystems are crucial for designing reliable and efficient synthetic biological devices. While growing demand for detection of low-level signals (e.g. traces of heavy metals or other contaminants) makes systems capable of signal amplification highly desirable, they may also be used to increase protein xpression after induction of a relatively weak promoter dependent on a commercially available nontoxic inducer, e.g. rhamnose. We have developed a synthetic bacterial memory based on previously described transctiptors [1, 2, 3], biological analogs of transistors using serine recombinases for specific DNA edition. Detection of an inducer results in discretization of the input signal and its storage across hundreds of E. coli generations. As glucose has been shown to inhibit expression in systems dependent on promoters containing a Crp binding site , it was possible to use a promoter that would be induced by a sugar inducer and strongly repressed by glucose, ensuring tight control over the input signal. In order to make the system more reliable and less noise-sensitive, the promoter was coupled with a synthetic RNA thermometer based on a previously described U10 thermometer [5, 6], modified to become compatible with the BioBrick standard. Secondary structures and free energies of designed candidate thermometers have been predicted using mfold web server [7, 8]. Resulting promoter forms a biological AND logic gate, demanding a certain inducer to enable transcription, and a certain temperature to enable translation of a target recombinase. If those two conditions are satisfied, high expression of an output protein is enabled. The functioning of the system has been assessed using his-tagged superfolder GFP as a reporter.
Bartoszewicz J., Nowicka, M., Krzynowek, W., Rżosińska, K., Abramowski, S., Nuc, P., Amplifying bacterial memory controlled by a synthetic RNA thermometer and a nontoxic inducer.