Abstract
When conditions are unfavorable, virtually all living cells have the capability of entering a resting state termed quiescence or G0. Many aspects of the quiescence program as well as the mechanisms governing the entry and exit from quiescence remain poorly understood. Previous studies using the budding yeast Saccharomyces cerevisiae have shown that upon entry into stationary phase, a quiescent cell population emerges that is heavier in density than nonquiescent cells. Here, we show that total intracellular trehalose and glycogen content exhibits substantial correlation with the density of individual cells both in stationary phase batch cultures and during continuous growth. During prolonged quiescence, trehalose stores are often maintained in favor over glycogen, perhaps to fulfill its numerous stress-protectant functions. Immediately upon exit from quiescence, cells preferentially metabolize trehalose over other fuel sources. Moreover, cells lacking trehalose initiate growth more slowly and frequently exhibit poor survivability. Together, our results support the view that trehalose, which is more stable than other carbohydrates, provides an enduring source of energy that helps drive cell cycle progression upon return to growth.