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From 2011.igem.org

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Module 1: Phyto-Route

Chemotaxis is the movement of bacteria based on attraction or repulsion of chemicals. Roots secrete a variety of compounds that E. coli are not attracted to naturally. Accordingly, we engineered a chemoreceptor into our chassis that can sense malate, a common root exudate, so that it can swim towards the root. Additionally, E. coli are actively taken up by plant roots, which will allow targeted IAA delivery into roots by our system.

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Specifications

1. The bacteria should actively move towards roots.

• For this, the bacteria need to be able to sense a common root exudate. We have chosen E. coli chemotaxis to be rewired towards malic acid (also referred to as malate), a compound found in the TCA cycle. It is released from the roots at low concentrations.

2. Uptake of bacteria into roots.

• We want the bacteria to get taken up into the plant roots to ensure that the concentration of indole-3-acetic acid (IAA) in the plant is increased. If the bacteria remained outside the roots, this goal may also be reached but it may be harder to increase internal IAA concentration. In addition, uptake of bacteria into the roots followed by secretion of chemicals presents a novel platform for modifying plants without genetically modifying the plant genomes.

3. The construct must be as modular as possible.

• Early on in our project we discovered (thanks to the modellers) that different concentrations of chemoreceptors on the surface of the cell allows the chemotaxis pathway to be saturated at different concentrations of malate. This means that we might be able to control the exact distance at which the chassis will stop making a bias walk towards the plant. Therefore, allowing us to test this construct with different promoters might allow us to study this phenomenon.