Uncoupling reproduction from metabolism extends chronological lifespan in yeast

Abstract

Studies of replicative and chronological lifespan in Saccharomyces cerevisiae have advanced understanding of longevity in all eukaryotes. Chronological lifespan in this species is defined as the agedependent viability of nondividing cells. To date this parameter has only been estimated under calorie restriction, mimicked by starvation. Because postmitotic cells in higher eukaryotes often do not starve, we developed a model yeast system to study cells as they age in the absence of calorie restriction. Yeast cells were encapsulated in a matrix consisting of calcium alginate to form ∼3 mm beads that were packed into bioreactors and fed ad libitum. Under these conditions cells ceased to divide, became heat shock and zymolyase resistant, yet retained high fermentative capacity. Over the course of 17 d, immobilized yeast cells maintained >95% viability, whereas the viability of starving, freely suspended (planktonic) cells decreased to <10%. Immobilized cells exhibited a stable pattern of gene expression that differed markedly from growing or starving planktonic cells, highly expressing genes in glycolysis, cell wall remodeling, and stress resistance, but decreasing transcription of genes in the tricarboxylic acid cycle, and genes that regulate the cell cycle, including master cyclins CDC28 and CLN1. Stress resistance transcription factor MSN4 and its upstream effector RIM15 are conspicuously up-regulated in the immobilized state, and an immobilized rim15 knockout strain fails to exhibit the long-lived, growth-arrested phenotype, suggesting that altered regulation of the Rim15-mediated nutrient-sensing pathway plays an important role in extending yeast chronological lifespan under calorie-unrestricted conditions. cell longevity | Ca-alginate encapsulation U nicellular microbes senesce and die (for reviews, see refs.

Matrices (re)loaded: Durability, viability, and fermentative capacity of yeast encapsulated in beads of different composition during long‐term fed‐batch culture

“…Planktonic S. cerevisiae cultured in nutrient-limited retentostats retain 80% viability after 22 days,99 and alginate-encapsulated yeast continuously fed ad libitum exhibited >90% viability after almost 3 weeks continuous culture 42. The lower viability reported here may stem from cells being subjected to repeated cycles of feast and famine, each of which F I G U R E 4 Cell escape over time.…”

“…42 Increased heat resistance displayed by encapsulated cells was once attributed to nutrient deficiency in cells close to the core of the bead, triggering a stress response similar to that observed for cells entering stationary phase. 115 Encapsulated cells are demonstrably heat-shock tolerant ( Figure 6) 42,116 ; others have shown that as much as 25% of this phenotype can be attributed to protection by the matrix itself. 115 Encapsulated cells are demonstrably heat-shock tolerant ( Figure 6) 42,116 ; others have shown that as much as 25% of this phenotype can be attributed to protection by the matrix itself.…”

Physiological and Transcriptional Responses of Different Industrial Microbes at Near-Zero Specific Growth Rates

“…Growth limitation by a nonenergy substrate can be explored, provided that overflow metabolism and reduced efficiency of energy source utilization under such energy excess conditions (90,91) can be prevented. Moreover, cell division can be uncoupled from metabolic activity under glucose excess by continuous cultivation of S. cerevisiae in alginate beads (92).…”

Live fast, die soon: cell cycle progression and lifespan in yeast cells

“…Under these unrestricted nutrient conditions, yeast ceases to divide, remains metabolically active, and exhibits no decline in viability over 2 weeks of continuous culture, a condition that produces proliferation arrest in the presence of nutrients. This effect is totally lost in a rim15 ∆ yeast strain 21. Thus, it appears that when the cell cycle is arrested or compromised, for whatever the reason, CLS increases.…”