Typically the chronological life span of yeast is measured by growing cells to saturation, plating a subset of the culture onto nutrient-rich YEPD plates, and counting the resulting colony forming units (CFUs) over time. We have developed a novel high-throughput method for measuring the chronological life span of the yeast Saccharomyces cerevisia that calculates viability of aged cells by measuring the shift in growth curves over a set time course. This method retains the same accuracy in measuring viability as the CFU method does while greatly increasing the potential data output. You can read more about our method here. In addition, we are in the process of creating a website open for anyone to use that greatly simplifies data analysis when using this method.
Using this method, we recently found that growth in standard synthetic defined medium results in an acidification of the culture supernatant which correlates with a reduction in the chronological life span of the budding yeast Saccharomyces cerevisia. Dietary restriction, growth in a non-fermentable carbon source such as glycerol, or transferring the cells to water results in lower levels of acidic byproducts in the yeast cultures. Further tests identified acetic acid as a cell-extrinsic mediator of cell death during the life span (see figure, taken from Burtner et al., Cell Cycle, 2009). In addition, several long-lived mutant s including sch9Δ and ras2Δ cells showed an increased resistance to acetic acid. These results indicate the extracellular environment plays a significant role in determining the chronological life span of yeast.
To follow up on this idea, we have performed a screen of the ORF deletion collection to identify single gene deletion mutants that do not acidify their supernatant to the same degree as wild-type cells. Several mutants have been found that have a higher culture pH as well as being significantly longer lived than wild-type cells and are being investigated further.
People: Chris Murakami