Quantification of random motility and chemotaxis bacterial transport coefficients using individual‐cell and population‐scale assays

Abstract

A number of individual-cell and population-scale assays have been introduced to quantify bacterial motility and chemotaxis. The transport coefficients reported in the literature, however, span several orders of magnitude, making it difficult to ascertain to what degree variations in bacterial species/strain, growth medium, growth and experimental conditions, and experiment type contribute to the reported differences in coefficient values. We quantified the random motility of Escherichia coli AW405 using the capillary assay, stopped-flow diffusion chamber (SFDC), and tracking microscope. We obtained good agreement for the random motility coefficient between these assays when using the same bacterial strain and consistent growth and experimental conditions. Chemotaxis of E. coli toward the attractant alpha-methylaspartate was quantified using the SFDC and capillary assay. Good agreement for the chemotactic sensitivity coefficient between the SFDC and the capillary assay was obtained across a limited attractant concentration range. Three different mathematical models were considered for analyzing capillary assay data to obtain a chemotactic sensitivity coefficient. These models differed by their treatment of the bacterial concentration in the chamber and the attractant concentration at the mouth. Results from our study indicate that the capillary assay, the most commonly used bacterial random motility and chemotaxis assay, can be used to accurately quantify bacterial transport coefficients over a limited range of attractant concentrations, provided experiments are performed carefully and appropriate mathematical models are used to interpret the experimental data.

Overview of Mathematical Approaches Used to Model Bacterial Chemotaxis II: Bacterial Populations

“…The first considered a population of 1,166 cells swimming in a three-dimensional environment, while the second looked at an individually tethered cell. The single cell behavior compared well with that observed by Korobkova et al (2004) and details on the diffusion rate of the population compared well with the experimentally known values of Lewus and Ford (2001) and Berg and Turner (1993). Whilst both models have sought to determine the effect that single cell behavior has on the population scale, both models have not systematically studied the effect that individual cell characteristics, such as receptor sensitivity, excitation, adaptation, motor response, and variations in them have on the population scale.…”

“…The bacteria were then observed to move up the tube in the direction of the attractant gradient forming bands as they did so. This assay has since become one of the most widely used methods for studying the response of bacterial populations to chemoattractants and in testing and validating mathematical models developed to describe bacterial chemotaxis (Lewus and Ford, 2001). A considerable amount of theoretical work has focused on understanding the formation of bacterial bands as detailed in Section 2.2.…”

Processes in microbial transport in the natural subsurface

“…In addition, the chemotactic capability of a given organism can vary depending on the nutrient to which it is being attracted. However, only a small fraction of the many organismnutrient systems found in natural subsurface conditions and bioremediation schemes have been studied (see Lewis and Ford [68] for a compilation of random motility and chemotactic sensitivity coefficients that have been reported for a few different organisms and nutrients). Therefore, these organism-specific and nutrient-specific transport characteristics have not been incorporated into predictive models of microbial transport applicable for field-scale hydrogeological applications.…”

Continuous-Flow Capillary Assay for Measuring Bacterial Chemotaxis

“…Poorly defined conditions in the pool can occur as a result of poorly defined convective flow that disturbs chemical and bacterial gradients (72) and/or by sedimentation of bacteria (14,58). Simplifications of the bacterial and chemoattractant concentrations at the capillary mouth (31) can be made so that only the capillary needs to be modeled, but the simplifications can have a significant impact on estimates of motility parameters, such as chemotactic sensitivity (46,49). The continuous-flow capillary assay eliminates consideration of the pool of bacteria because constant-concentration conditions at the mouth of the capillary are created by the flowing bacterial suspension.…”

“…This expression has been used successfully to simulate chemotactic migration of bacteria (46,50). The chemotactic sensitivity coefficient was quantified using a finite-difference numerical model (50) with constant-concentration conditions at the mouth of the capillary.…”