Team:Harvard BioDesign/Description
Parts Characterization
We used the rhamnose promoter BBa_K902065 in our fimH plasmid, with the intention of controlling the amount of FimH produced. Prior research indicates that there is some question as to whether rhamnose is actually titratable. That is, when a population of cells containing plasmids with the rhamnose promoter is induced, the effect that the inducer has on the population appears to be increasing linearly with the amount of inducer. But evidence in the literature suggests that at the single cell level, each cell is either completely induced or completely uninduced. Thus while rhamnose appears to be titratable on the population level, it is possible that there is no expression over some subset of cells and 100% expression over another. We wanted to see if this was the case for BBa_K902065.
We found an existing iGEM part that contained BBa_K902065 and expressed GFP. Using this part, we induced with varying concentrations of rhamnose. We performed flow cytometry to measure the fluorescence of individual cells. Our results show the distribution of the fluorescence. Our data shows that there is an intermediate concentration of inducer for which part of the population shows the same fluorescence as the control population with no inducer added. This result confirms that the rhamnose promoter is bimodal; that is, each cell is turned either completely off or completely on when inducer is added. This result is interesting for our project because it shows that we cannot control the level of fimH production of each cell, but only that of the cell population as a whole.