UnLeish
In this project, we aim to engineer a bacteria (which we've named UnLeish! ) which will be taken up by immune cells like the macrophage and dendritic cells using phagocytic processes. Once inside a macrophage, the bacterium will sense whether the macrophage is infected by Leishmania or not, by sensing its microenvironment (i.e. nitric oxide level) inside the phagolysosome and in response to this, it will conditionally start the expression of iron chelating compounds (Aerobactin). This will serve two purposes - firstly, these iron chelating compounds will deprive the Leishmania, which grows slower than our bacterial chassis, of much-needed iron which is required for its replication, by depleting the labile iron pool inside the phagolysosome.
Secondly, it also acts as a temporary survival factor (because the bacteria can use the iron bound to aerobactin to accelerate their own growth) for the bacteria, which prolongs their life inside the Leishmania-infected macrophage. This is to ensure that the bacteria survives for a long enough time, to effectively compete with Leishmania for iron inside the phagolysosome. On the other hand, in uninfected macrophages, our bacterium can be easily killed due to greater immune response in the absence of Leishmania, and also due to the lack of aerobactin expression leading to iron-depleted conditions. Moreover, since the growth rate of bacteria is much faster than that of Leishmania, the number of bacteria inside the phagolysosome will increase. At a certain population density of bacteria, the bacteria will start the expression of pyruvate oxygenase, an enzyme which produces a reactive oxygen species, using a quorum sensor-based induction circuit. This ROS burst will effectively kill both the remaining Leishmania parasite and our engineered bacteria inside the phagolysosome. |
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