Everyone loves the scent of freshly baked bread. Or perhaps you’re more partial to the smells coming from your favorite brewery. Either way, bread and beer have one important tiny organism in common – yeast! Yeast allows for the good flavors to be released in both rising dough and brewing beer. Saccharomyces cerevisiae is the scientific name for bakers and brewers yeast; it is also one of the beneficial residents of our gut, helping with healthy digestion.
Yeast is often used in scientific studies to map cellular functions to human biology and help us better understand and treat disease. One of the reasons scientists like to use yeast in the lab is that it grows quickly and is easy to track how a population of cells can change over time.
Lydia Heasley, PhD, is a Colorado native who runs a research lab on the University of Colorado Anschutz Medical Campus in Aurora. Her research group is studying how the behaviors and functions of yeast change when their environment causes stress. We know that the ability to adapt to a changing environment is critical to survival for all forms of life, including humans and yeast. In order to adapt, mutations or changes to the genetic code – the recipe book with instructions for how to make each component of our cells – are essential.
Changes in the blueprint of life
You might hear or read the word ‘mutation’ and immediately think of a negative outcome. That’s not always the case! Mutations or changes to the genetic code do not always produce negative outcomes. Did you know that humans who enjoy milk and any other dairy products are benefiting from a commonly passed down mutation?!? This mutation allows us to digest things like ice cream. People who don’t have the mutation are lactose intolerant and are unable to easily digest milk products.
Mutations can be additions or deletions of genetic information or mistakes — kind of like misspelling a word (e.g. mistake: mistacke, misteak, mestake). Sometimes a mutation is silent, in that it doesn’t affect the outcome of the recipe – like swapping one brand of milk chocolate chips for another brand in cookies. Sometimes a mutation causes a negative change, like mistakenly putting salt instead of sugar into your cookies. Other times mutations cause new and beneficial outcomes, such as adding peanut butter into your cookie batter for a new delicious flavor.
Scientists like Lydia look at mutations in yeast to understand how a population of cells can change over time by studying which mutations they keep around (like our ability to digest milk products) and which mutations they get rid of.
Studying mutations in yeast cells
The science being done in Heasley’s lab looks at how new mutations allow yeast cells to switch between different behaviors and functions even when there is not a specific cue from their surroundings. New mutations are thought to allow the yeast cells to quickly test out many new abilities and hedge their bets so that the population of cells as a whole has a better chance to adapt to and survive in their environment no matter what new conditions come their way.
Heasley’s lab is performing experiments that use strains of yeast that have been thoroughly studied and are well understood. To learn even more about the ability of yeast cells to change and adapt, they are also studying a variety of other yeast strains that have been isolated from environments in the wild which have been subjected to different environmental stressors. The lab has compared mutations found across the different species and discovered that new abilities like changes in colony shape (see image) or surviving different drug treatments is frequently caused by large mutations which impact the number, size and shape of chromosomes – the structures that contain the genetic code.
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Yeast colony shapes change spontaneously as they grow over time – these photos were taken over a 24-hour (1-day) period!
Exciting news from this research is that the observed changes in yeast chromosomes are important for causing changes in cellular behavior and contribute to the random mutations found in wild yeast strains. These changes are suspected to help populations of cells better survive rapidly changing environments.
These studies in Heasley’s research lab on yeast are important to human health. The discoveries from her lab will help us to figure out how to combat certain fungi (also known as ‘yeast’) that infect humans. Many of these types of infections have become hard to treat because they have taken on genetic changes that have allowed them to become resistant to current drug treatments.
Heasley and her research team will continue to investigate how yeast cells change over time and how the loss or gain of genetic material might contribute to antifungal drug resistance.
Guest contributor: Lydia Heasley, PhD, is an assistant professor in the Department of Biochemistry and Molecular Genetics at the University of Colorado School of Medicine.
