ALT Pictured is a composite image showing trajectories of the green algae Chlamydomonas reinhardtii and the distribution of the bacterium Bacillus subtilis. Praneet Prakash, Yasa Baig, et al. created a system in which a shaft of visible light illuminates a thin fluid chamber containing a flagella-less mutant of C. reinhardtii and yellow fluorescently labelled B. subtilis. The illuminated algae photosynthetically produce oxygen, while bacteria chemotactically move inwards, and then, strikingly, the algae are expelled from the illuminated region along with a fraction of the bacteria, which form a thin annulus at the light/dark boundary.