At neutral pH the chronological lifespan of Hansenula polymorpha increases upon enhancing the carbon source concentration

Dietary restriction is generally assumed to increase the lifespan in most eukaryotes, including the simple model organism Saccharomyces cere- visiae. However, recent data questioned whether this phenomenon is indeed true for yeast. We studied the effect of reduction of the carbon source con- centration on the chronological lifespan of the yeast Hansenula polymorpha using four different carbon sources. Our data indicate that reduction of the carbon source concentration has a negative (glucose, ethanol, methanol) or positive (glycerol) effect on the chronological lifespan. We show that the ac- tual effect of carbon source concentrations largely depends on extracellular factor(s). We provide evidence that H. polymorpha acidifies the medium and that a low pH of the medium alone is sufficient to significantly decrease the chronological lifespan. However, glucose-grown cells are less sensitive to low pH compared to glycerol-grown cells, explaining why only the reduction of the glycerol-concentration (which leads to less medium acidification) has a posi- tive effect on the chronological lifespan. Instead, the positive effect of en- hancing the glucose concentrations is much larger than the negative effect of the medium acidification at these conditions, explaining the increased lifespan with increasing glucose concentrations. Importantly, at neutral pH, the chronological lifespan also decreases with a reduction in glycerol concen- trations. We show that for glycerol cultures this effect is related to acidifica- tion independent changes in the composition of the spent medium. Altogeth- er, our data indicate that in H. polymorpha at neutral pH the chronological lifespan invariably extends upon increasing the carbon source concentration