Fig. 1.

Seawater bacteria respond to ephemeral DOM gradients from phytoplankton. (A–C) Swimming trajectories (white) of bacteria demonstrate ephemeral accumulations or ‟clusters” around natural phytoplankton including Chaetoceros sp. (aqua outline), Ceratium sp. (red), Asterionella sp. (green), and Skeletonema sp. (orange). The image at each time point is the maximum intensity projection from a movie (Movie S1). (D) Chemotactic cluster formation around the cultured diatom C. affinis. Contours show the enhancement of motile bacteria over background concentration during the 30 s immediately following cell lysis (Fig. S4). White tracks are bacterial trajectories over 2 s.