Chemotaxis is the movement of an organism in response to an external chemical stimulus.
Many single-cell and multicellular organisms use chemotaxis to navigate their immediate environment.

The E. coli chemotaxis system is considered a model system that illustrates some of the core principles of chemotactic movement (1). It allows the cell to sense and quickly respond to nearby nutrients – attractants, and dangerous chemicals – repellents.

A detailed explanation on the chemotaxis system and the intercellular processes involved can be found here.

Fig. 1: Chemotaxis concept (1).

Bacterial chemotaxis is mediated by chemoreceptors. The purpose of these membrane proteins is to bind a certain chemoeffector, and transduce the signal to the downstream proteins.

The specificity of a chemoreceptor is determined by its ligand binding domain – the transmembrane region of the receptor. We have chosen this domain as the focus of our project.

Fig. 2: Chemoreceptor structure illustration.

Project Super Tar - S.Tar in short, is designed to be a novel broadband platform for chemical detection technology using controlled chemotaxis. The base of our project is the E. coli Tar chemoreceptor or more specifically, its ligand binding domain (LBD).
We show that by mutating the native Tar LBD (2) or by interchanging it with that of other receptors (3), the E. coli chemotaxis system can be programmed to respond to completely new ligands.

Fig. 3: S.Tar project - Programming the chemoreceptors to respond to new ligands by modifying the ligand binding domain.

To demonstrate the potential of our system, we performed two experiments:
1. We replaced the Tar LBD with that of the PctA chemoreceptor and demonstrated a chemotactic response to its repellent – TCE, a substance which the native Tar cannot recognize.
2. We used computational biology to redesign the native Tar receptor to bind Histamine instead of its original ligand- Aspartate. We demonstrated a chemotactic response from the mutated receptor.

Using S.Tar, scientists will be able to control the movement of bacteria and direct them towards or away from a target material. This system can have vast applications in bioremediation and, as we show in our project, detection.

As an application of our system, we designed an easy-to-use detection system, which utilizes the high sensitivity of the chemotactic response. FlashLab (link to flashlab page) is a simple and cheap platform for the detection of any chemoeffector, using S.Tar bacteria.

Fig. 4: Flash Lab - our designed detection chip.