Quantification of chemotaxis to naphthalene by Pseudomonas putida G7

The capillary assay was used to quantify the chemotactic response of Pseudomonas putida G7 to naphthalene. Experiments were conducted in which the cell concentration in the assay chamber, the naphthalene concentration in the capillary, or the incubation time was varied. Data from these experiments were evaluated with a model that accounted for the effect of diffusion on the distribution of substrate and the transport of cells from the chamber through the capillary orifice. By fitting a numerical solution of this model to the data, it was possible to determine the chemotactic sensitivity coefficient, chi0. The mean of the best-fit values for chi0 from the three types of experiments was 7.2 x 10(-5) cm2/s. A less computationally intensive model based on earlier approaches that ignore cell transport in the chamber resulted in chi0 values that were approximately three times higher. The models evaluated in the present study could simulate the results of capillary assays only at low chamber cell concentrations, for which the effect of consumption on the distribution of substrate was negligible. Results from this work suggest that it is possible to use the capillary assay to quantify taxis towards environmentally relevant chemoeffectors that have low aqueous solubility.