FIGURE 1.

Attractant degradation increases the range and concentration robustness of chemotaxis. (A) Simulations of a gradient chamber assay with and without attractant degradation after 1 h at low (0–300 nM gradient vs uniform 300 nM), intermediate (0–3 μM vs uniform 3 μM), and high concentrations (0–30 μM vs uniform 30 μM). (B) Fraction of cells (response score) passing 400 μm after 1 h across a range of concentrations with (red) and without (black) attractant degradation. (C) Example long range chemotaxis of self-generated gradient across three orders of magnitude. At 1 μM, the gradient produced by cells eventually becomes too shallow for optimal chemotaxis. At 10 μM, the gradient remains steep and the wave of cells remains cohesive. At 100 μM, the cells are at first unable to degrade attractant as rapidly as diffusion delivers it to them, causing a delay before the leading wave of cells forms. Though this wave performs well once formed, it covers less distance over the allotted time due to this delay effect. Shown below is the response to a linear gradient of 0–10 μM over the same distance. (D) Distance covered by the leading 10 cells at 2, 4, and 6 h by a self-generated gradient at various concentrations. (E) Time taken for 100 cells to pass 1 mm across many saturating concentrations. The graph has distinct linear and non-linear regions, showing that, after a certain point, twice the attractant leads to (approximately) twice the delay before a wave develops.