Microorganisms have evolved to survive under adverse conditions, such as starvation, that are commonly encountered in the wild. In fact, most microorganisms are estimated to survive in a low-metabolism stationary phase under nutrient-depleted conditions (Werner-Washburne et al., 1996). In the wild, yeast organisms are likely to exit stationary phase only during the rare periods when all the nutrients required for growth become available. For this reason we perform most of our experiments in either a medium containing a limited amount of nutrients [synthetic dextrose complete (SDC)] or in water. Wild-type DBY746 or SP1 yeast grown in SDC medium survive 5 to 6 days while maintaining high metabolic rates for the majority of the life span (Figure 19.1).
When yeast grown in SDC are switched to water between days 1 and 5, metabolic rates decrease and survival is extended (Fabrizio et al., 2004a). However, since long-lived mutants isolated by incubation in SDC also live longer when incubated in water, we believe that analogous pathways and mechanisms regulate survival in both paradigms. Yeast grown and incubated in the nutrient-rich YPD medium also survive for months in a low metabolism stationary phase. However, it is not clear whether YPD medium allows some growth to occur during the supposedly "stationary" phase (see Survival in Water/YPD).
To understand how yeast age and to identify conserved pathways that regulate longevity in many eukaryotes,
Mutants, mutagenized yeast,
YKO collection &
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