Oxygen toxicity in a polyamine-depleted spe2 delta mutant of Saccharomyces cerevisiae.

When a mutant of Saccharomyces cerevisiae (spe2 delta) that cannot make spermidine or spermine was incubated in a polyamine-deficient medium in oxygen, there was a rapid cessation of cell growth and associated cell death. In contrast, when the mutant cells were incubated in the polyamine-deficient medium in air or anaerobically, the culture stopped growing more gradually, and there was no significant loss of cell viability. We also found that the polyamine-deficient cells grown in air, but not those grown anaerobically, showed a permanent loss of functional mitochondria ("respiratory competency"), as evidenced by their inability to grow on glycerol as the sole carbon source. These data support the postulation that polyamines act, in part, by protecting cell components from damage resulting from oxidation. However, since the mutant cells still required spermidine or spermine for growth when incubated under strictly anaerobic conditions, polyamines must also have other essential functions.