Heterogeneity of stress gene expression and stress resistance among individual cells of Saccharomyces cerevisiae

Abstract

Knowledge of gene expression and cellular responses in microorganisms is derived from analyses of populations consisting of millions of cells. Analytical techniques that provide data as population averages fail to inform of culture heterogeneity. Flow cytometry and fluorescence techniques were used to provide information on the heterogeneity of stress‐responsive gene expression and stress tolerance in individual cells within populations. A sequence of DNA encoding the heat shock and stress response elements of the Saccharomyces cerevisiae HSP104 gene was used to express enhanced green fluorescent protein (EGFP). When integrated into the genome of yeast strain W303‐1A, intrinsic expression of EGFP increased about twofold as cells progressed from growth on glucose to ethanol utilization in aerobic batch cultures. Staining of cells with orange/red fluorescent propidium iodide (PI), which only enters cells that have compromised membrane integrity, revealed that the population became more tolerant to 52°C heat stress as it progressed from growth on glucose and through the ethanol utilization phase of aerobic batch culture. Exposure of cultures growing on glucose to a mild heat shock (shift from 25°C to 37°C) resulted in significantly increased expression of EGFP in the population. However, there was heterogeneity in the intensity of fluorescence of individual cells from heat‐shocked cultures, indicating variability in the strength of stress response in the clonal population. Detailed analysis of the heterogeneity showed a clear positive trend between intensity of stress response and individual cell resistance, measured in terms of PI exclusion, to heat stress at 52°C. Further experiments indicated that, although the mean gene expression by a population is influenced by the genetic background, the heterogeneity among individual cells in clonal populations is largely physiologically based.

Two Subpopulations of Listeria monocytogenes Occur at Subinhibitory Concentrations of Leucocin 4010 and Nisin

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“…This has been a highly active area of basic research in recent years, with some ground-breaking work revealing the underlying mechanisms and consequences of this property. Indeed, phenotypic heterogeneity even within clonal cell populations is a well-observed phenomenon in a wide range of cell types including bacteria (Avery 2005), yeast (Attfield et al 2001), and mammalian cells, making the term "clonal heterogeneity" less an oxymoron and more a statement of an inescapable fact of biological systems. This clonal phenotypic heterogeneity can be explained by a combination of local micro-variations in the culture environment, random partitioning of organelles into daughter cells at cell division, and the stochastic "bursting" nature of gene transcription (Molina et al 2013;Raj and van Oudenaarden 2008;Raj et al 2006).…”

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