title: Experimental verification of the behavioral foundation of bacterial transport parameters using microfluidics.
abstract: We present novel microfluidic experiments to quantify population-scale transport parameters (chemotactic sensitivity chi(0) and random motility mu) of a population of bacteria. Previously, transport parameters have been derived theoretically from single-cell swimming behavior using probabilistic models, yet the mechanistic foundations of this upscaling process have not been verified experimentally. We designed a microfluidic capillary assay to generate and accurately measure gradients of chemoattractant (alpha-methylaspartate) while simultaneously capturing the swimming trajectories of individual Escherichia coli bacteria using videomicroscopy and cell tracking. By measuring swimming speed and bias in the swimming direction of single cells for a range of chemoattractant concentrations and concentration gradients, we directly computed the chemotactic velocity VC and the associated chemotactic sensitivity chi(0). We then show how mu can also be readily determined using microfluidics but that a population-scale microfluidic approach is experimentally more convenient than a single-cell analysis in this case. Measured values of both chi(0) [(12.4 +/- 2.0) x 10(-4) cm(2) s(-1)] and mu [(3.3 +/- 0.8) x 10(-6) cm(2) s(-1)] are comparable to literature results. This microscale approach to bacterial chemotaxis lends experimental support to theoretical derivations of population-scale transport parameters from single-cell behavior. Furthermore, this study shows that microfluidic platforms can go beyond traditional chemotaxis assays and enable the quantification of bacterial transport parameters.
authors.affiliation: Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Tanvir
authors.initials: T
authors.lastname: Ahmed
authors.forename: Roman
authors.initials: R
authors.lastname: Stocker
mesh_terms: D002630:Chemotactic Factors / Q000494:pharmacology; D002633:Chemotaxis / Q000187:drug effects; D004926:Escherichia coli / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D046210:Microfluidic Analytical Techniques; D013997:Time Factors
chemical_list: D002630:Chemotactic Factors