bioRxiv · 2026-05-23
Scientists discovered that cyanobacteria (ancient photosynthetic microbes) absolutely depend on their stored sugar (glycogen) to survive the night and restart growth at dawn. Without it, their energy systems collapse in the dark and they struggle to divide when light returns.
Glycogen-deficient mutants showed severe energy depletion at night, with reduced ATP levels and depleted central carbon metabolites, demonstrating glycogen is the primary nighttime fuel source.
During daytime, mutant cells compensated by downregulating photosynthesis genes to avoid dangerous energy overload — a stress response that limited their ability to grow normally.
After dawn, glycogen-deficient cells experienced extended lag phases and delayed cell divisions, showing they could not efficiently restart growth without overnight glycogen reserves.