Circadian clocks are oscillatory systems that allow organisms to anticipate rhythmic changes in the environment. Several studies have shown that circadian clocks are connected to metabolism, but it is not generally clear whether metabolic signaling is one voice among many that influence the clock or whether metabolic cycling is the major clock synchronizer.
To address this question in cyanobacteria, researchers used a synthetic biology approach to make normally autotrophic cells capable of growth on exogenous sugar. This allowed them to manipulate metabolism independently from light and dark.
The authors found that feeding sugar to cultures blocked the clock-resetting effect of a dark pulse.
Furthermore, in the absence of light, the clock efficiently synchronizes to metabolic cycles driven by rhythmic feeding.
They conclude that metabolic activity, independent of its source, is the primary clock driver in cyanobacteria.