Quantification of bacterial chemotaxis by measurement of model parameters using the capillary assay

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Abstract
The capillary assay for quantitative characterization of bacterial motility and chemotaxis is analyzed in terms of a mathematical model for cell population migration, in order to determine values for the cell random motility coefficient, μ and the cell chemotaxis coefficient, χ. The analysis involves both analytical perturbation methods and numerical finite-difference techniques. Transient cell density profiles within the capillary tube are determined as they depend upon μ and χ, providing a means for estimating μ and χ from the common protocol measurements of cell accumulation in the tube at specified observation times. The effects of extraneous factors such as assay geometry, stimulus diffusivity, bacterial density, and observation time are thus separated from the intrinsic cell–stimulus interaction and response. This allows independent population measurements of cell chemosensory movement properties to be extrapolated to situations involving growth and competition of populations, for purposes of better understanding microbial population dynamics in systems of biotechnological and microbial ecological importance.