Chemotaxis coefficient

In the second case, single population growth of a chemotactic species, B additionally depends upon 6, the ratio of the chemotaxis coefficient to the random motility coefficient (see Figure 9). B increases as 6 increases, because chemotaxis counteracts the random dispersal of cells away from the nutrient-rich zone (see Figure 10 ) The effect of chemotaxis becomes significant only when 6 becomes greater than about 10 1. These computations were done using a perturbation method, so that results for 6> 1 are merely extrapolations. Numerical computations have shown the perturbation results to be accurate up to at least 6 =... 

Ford, R.M., Phillips, B.R., Quinn, J.A. and Lauffenburger, D.A. (1991). Measurement of bacterial random motihly and chemotaxis coefficients. 1. Stopped-flow diffusion chamber assay. Biotechnol. Bioengineer. 37, 647-660. 

This assay is a variation of the cellulose filter assay that uses multiple arrangements of chemoattractant above and below the filter to distinguish chemokinesis and chemotaxis. In addition, the depth to which the cells penetrate the filter is determined. These features allow calculation of population parameters x, the random motility coefficient and X, a chemotaxis coefficient. 

TranquiUo, R.T., Zigmond, S.H. and Lauffenburger, D.A. (1988). Measurement of the chemotaxis coefficient for human neutrophils in the under-agarose migration assay. Cell Motil. Cytoskeleton 11, 1-15. 

We generally assess the protein concentration of new chemokine stock solutions by OD280 using the appropriate extinction coefficient for each chemokine or by Bradford assay. Although this is not often practical when very small quantities of chemokine are purchased because 10-20% of the material may be sacrificed for an accurate determination, we have found that the actual protein concentration may vary by as much as 2CM-0% between lots which can significantly effect the reproducibility of chemotaxis assays. 

Based on the quantifled images, the chemotaxis partition coef-flcient (CPC) and the chemotaxis migration coefficient (CMC) can be calculated as described in (51). If a cell is detected on the high-concentration side (it migrates to the right), it is given a value of +1, whereas a cell detected on the low-concentration... 

Fig. 7. Quantification of co//RP437 chemotaxis in laFlow devices. Bacterial responses to gradients of 0-100 riM L-aspartate and 0-225 riM NiSO were quantified using image analysis. The data were used to calculate the chemotaxis partition coefficient (CPC) and chemotaxis migration coefficient (CMC). The CPC and CMC values shown correspond to the images shown in Fig. 4c and d.

If D is constant, (2.9) reduces to (2.3) in the one-dimensional case. In some models for insect populations, models for bacterial chemotaxis, or for animal grouping due to social aggregation, the diffusion coefficient can be an explicit function of the particle density or a function of other chemical components. 

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