Fig. 2.

Chemotactic accumulation in the phycosphere lasts ∼10 min and extends ∼2 mm from the diatom. All panels (A–D) show results for a prototypical radially symmetric cluster in response to lysis of a single C. affinis diatom. (A) Bacterial concentration above background as a function of distance from the diatom center, r, for three 30-s time windows after lysis. The prelysis background is also shown. An image of the lysed diatom (bottom left) shows relative bacterial concentration (color contours) at peak accumulation (t = 1 min), with the same scale as the x axis. (B) Brightness of the diatom center (in arbitrary units) showing the moment at which lysis occurred, t = 0. (C) Bacterial enhancement relative to the background concentration, B(r,t). (D) Relative concentration of the effective chemoattractant as a function of distance and time, C(r,t), determined from a mathematical simulation.