Plasticity of death rates in stationary phase in Saccharomyces cerevisiae

Abstract

SummaryFor the species that have been most carefully studied, mortality rises with age and then plateaus or declines at advanced ages, except for yeast. Remarkably, mortality for yeast can rise, fall and rise again. In the present study we investigated (i) if this complicated shape could be modulated by environmental conditions by measuring mortality with different food media and temperature; (ii) if it is triggered by biological heterogeneity by measuring mortality in stationary phase in populations fractionated into subpopulations of young, virgin cells, and replicatively older, non-virgin cells. We also discussed the results of a staining method to measure viability instead of measuring the number of cells able to exit stationary phase and form a colony. We showed that different shapes of age-specific death rates were observed and that their appearance depended on the environmental conditions. Furthermore, biological heterogeneity explained the shapes of mortality with homogeneous populations of young, virgin cells exhibiting a simple shape of mortality in conditions under which more heterogeneous populations of older cells or unfractionated populations displayed complicated death rates. Finally, the staining method suggested that cells lost the capacity to exit stationary phase and to divide long before they died in stationary phase. These results explain a phenomenon that was puzzling because it appeared to reflect a radical departure from mortality patterns observed for other species.

Dietary Restriction Depends on Nutrient Composition to Extend Chronological Lifespan in Budding Yeast Saccharomyces cerevisiae

“…Firstly, it allows isolation of quiescent and non-quiescent cells from the stationary phase cultures grown in the YPD medium [28], [40]. Secondly, the shape of mortality curves for yeast grown in the nutrient-rich YPD medium was similar to the mortality patterns observed in multicellular eukaryotes [41]. Furthermore, yeast grown in the YPD medium containing 0.2% or 0.5% glucose lived significantly longer than that grown at 0.05%, 1% or 2% glucose [27], which suggests that the glucose level affects lifespan of yeast as observed in many higher eukaryotes.…”

Characterization of the Viable but Nonculturable (VBNC) State in Saccharomyces cerevisiae

“…The percentage of yeast recovering culturability started to decrease after few days depending on the time they were kept in VBNC state. It can be speculated that, all cells did not resuscitate because of the heterogeneity of physiological states within the yeast population [36].…”

The essence of yeast quiescence

“…It is worth noting that stationary-phase cultures (defined as 4 7 days old) exhibit a complex, heterogeneous community structure, composed of a large fraction of quiescent, long-lived (almost exclusively daughter and young mother) cells and a nonquiescent fraction of cells, which rapidly lose their ability to reproduce and gradually accumulate ROS, exhibit genomic instability, and become senescent or apoptotic (Allen et al, 2006;Aragon et al, 2008;Davidson et al, 2011). This diverse array of physiologically different cell populations with both different reproductive histories and distinct survival rates [and hence different chronological life spans (CLS)] contributes to the temporal plasticity of the mortality rate (generally determined as the relative loss of CFUs) within an aging stationary-phase culture (Minois et al, 2009). Notably, both the heterogeneity within stationary-phase cultures and the fact that some of the reproductively incompetent, living cells remain unaccounted for by CFU measurements (Minois et al, 2009) were hitherto largely overlooked in various CLS studies.…”

“…This diverse array of physiologically different cell populations with both different reproductive histories and distinct survival rates [and hence different chronological life spans (CLS)] contributes to the temporal plasticity of the mortality rate (generally determined as the relative loss of CFUs) within an aging stationary-phase culture (Minois et al, 2009). Notably, both the heterogeneity within stationary-phase cultures and the fact that some of the reproductively incompetent, living cells remain unaccounted for by CFU measurements (Minois et al, 2009) were hitherto largely overlooked in various CLS studies. Nevertheless, genetic and physiological studies of aging factors that affect CLS in yeast, a potentially valuable model for aging in postmitotic mammalian cells (Fabrizio & Longo, 2003;Kaeberlein, 2010), have identified distinct properties of quiescent cells that collectively define the essence of the quiescence program in yeast.…”