Chemotaxis of Escherichia coli to controlled gradients of attractants : Experiments and Mathematical modeling

Chemotaxis is a phenomenon in which a microorganism or multi-cellular organisms are able to direct their movements in the presence of certain chemicals in their environment. This could be either towards favorable chemicals called chemoattractants or away from unfavorable chemicals called chemorepellents. The understanding of this phenomena is important in many biological processes including immune response, embryo-genesis, wound healing, bio-film formation and bio-remediation of subsurface contaminants. The objective of this thesis is to study the response of microorganisms in the presence of controlled gradients of chemoattractants using a micro-capillary. This would involve developing mathematical models that describe the chemotaxis pathway in a chemotactic cell and to relate the kinetics to the motion of cell in the presence of chemoattractants. The predictions of the model will be compared with experiments where the motion of cell in the presence of chemoattractants will be tracked. The previous studies have reported average drift velocities for a given gradient and do not measure drift velocities as a function of time and space. To address this issue, a novel experimental technique was developed to quantify the motion of E. coli cells to varying concentrations and gradients of chemoattractant so as to capture the spatial and temporal variation of the drift velocity. The statistics of single cell motions such as cell velocity, tumbling frequency, rotational diffusion, drift velocity and translational diffusivity are obtained independently. An existing two state receptor model of Barkai and Leibler (1997) was used for the intracellular pathway and into this the extra-cellular influence such as ligand concentration and Brownian motion was incorporated to predict the response for the experimental conditions. The model predicted the ex-