John Brooks is investigating how mammals’ internal clocks affect microbes that live in the gut. The mix of microbial species in these communities oscillates throughout the day. Scientists have linked these swings to the circadian clock, the biochemical timekeeper that governs everything from appetite to sleep. Brooks plans to unravel how the circadian clock works with the innate immune system to regulate microbe metabolism. His results could expose how the clock/microbiota interplay shapes the health of the host.