Function of trehalose and glycogen in cell cycle progression and cell viability in Saccharomyces cerevisiae

Trehalose and glycogen accumulate in Saccharomyces cerevisiae when growth c onditions deteriorate. It has been suggested that aside from functioning as storage factors and stress protectants, these carbohydrates may he require d for cell cycle progression at low growth rates under carbon limitation. B y using a mutant unable to synthesize trehalose and glycogen, we have inves tigated this requirement of trehalose and glycogen under carbon-limited con ditions in continuous cultures. Trehalose and glycogen levels increased wit h decreasing growth rates in the wild-type strain, whereas no trehalose or glycogen was detected in the mutant. However, the mutant was still able to grow and divide at low growth rates with doubling times similar to those fo r the wild-type strain, indicating that trehalose and glycogen are not esse ntial for cell cycle progression. Nevertheless, upon a slight increase of e xtracellular carbohydrates, the wild-type strain degraded its reserve carbo hydrates and was able to enter a cell division cycle faster than the mutant . In addition, wild-type cells survived much longer than the mutant cells w hen extracellular carbon was exhausted. Thus, trehalose and glycogen have a dual role under these conditions, serving as storage factors during carbon starvation and providing quickly a higher carbon and ATP flux when conditi ons improve, Interestingly, the CO, production rate and hence the ATP flux were higher in the mutant than in the wild-type strain at low growth rates. The possibility that the mutant strain requires this steady higher glycoly tic flux at low growth rates for passage through Start is discussed.