Team:Imperial College London/Project Chemotaxis Overview
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.
Figure 1: Escherichia coli cells expressing superfolder GFP (sfGFP) can be seen inside an Arabidopsis thaliana root using confocal microscopy after overnight incubation of the plants with bacteria. Roots were washed in PBS prior to imaging to avoid "false positives" of bacteria adhering to the outside of the root. For a cool 3D video of bacteria inside the roots, check out our Results page. (Data and imaging by Imperial iGEM 2011).
The Phyto-Route module mainly consists of bacterial movement towards plant roots. Following bacterial movement to the roots, the microbes are taken up into the roots themselves. The fact that bacteria are taken up into plant roots, where they are used for nutrients by the plant, is a novel finding that was only described last year when Paungfoo-Lonhienne et al.  reported the uptake of non-pathogenic Escherichia coli into the roots of Arabidopsis thaliana (watercress) and Lycopersicum esculentum (tomato plant). We have successfully replicated these findings (Figure 1). This is especially interesting for our project as the plants will be exposed to bacterial auxin inside the root cells, which significantly affects the concentration of IAA the bacteria need to produce to effect optimal root growth. In addition, Phyto-Route can potentially be used as a platform to deliver compounds, which would not naturally occur in the plant, into roots without genetically modifying the plant itself.
Our primary chassis for wet lab experiments is Escherichia coli. Chemotaxis in E. coli is well documented. These bacteria can perform two types of movement, tumbling and smooth swimming. The difference between the two is determined by flagellar movement. During tumbling movement, the flagella move clockwise. This is caused by the formation of a complex between CheY-P and FliM, one of the flagella-associated proteins. During smooth swimming, the flagella move counter-clockwise. CheY is not phosphorylated and therefore cannot associate with flagellar proteins, causing the flagella to rotate in the opposite direction.
Smooth swimming is the movement performed by bacteria towards an attractant or away from a repellent. Smooth swimming is controlled by a number of chemotaxis proteins that make up a signalling pathway, please see the demonstration below for details .
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 Paungfoo-Lonhienne C et al. (2010) Turning the table: plants consume microbes as a source of nutrients. PLoS One 5(7): e11915.
 Chelsky D and Dahlquist FW (1980) Chemotaxis in Escherichia coli: association of protein components. Biochemistry 19: 4633–4639.