Holly Senebandith

Mentor: Dr. Joshua Shapiro

Department of Biology


Isolation and Identification of Wild Yeast in Southeastern Pennsylvania


For millennia, humans have used yeast, in particular Saccharomyces cerevisiae, to produce many types of alcoholic beverages as well as other culinary delights.  Because of S. cerevisiae’s extensive use in the domestic sphere, it is commonly referred to as “baker’s yeast.” For a while, it was unclear whether or not the S. cerevisiae found in nature actually existed as wild strains or had simply escaped from domestically used strains.  However, research has shown S. cerevisiae to exist in the wild, especially in the soil and bark of oak trees.  Despite the length of time humans have utilized yeast, many questions still remain about the nature of wild S. cerevisiae


This research will begin to skim the surface of these unanswered questions by determining how common wild S. cerevisiae is relative to other species of wild yeast that grow in the same environment, and also how the population of wild S. cerevisiae changes yearly and throughout the different seasons. 


By collecting samples primarily from oak tree soil, we will attempt to isolate wild yeast using two different enrichment media in order to survey the species (and genetic) diversity of wild yeast at Bryn Mawr College.  These media, one with high sugar content and one with high alcohol content, will both select for yeast.  The former medium will allow the yeasts to outcompete other microorganisms, such as bacteria, because of yeasts’ ability to break down sugars.  The latter medium, containing high alcohol content, will select for yeasts because of their ability to survive in environments of high alcohol content.  Using these two media, we will be looking to see if one medium selects more or less effectively for wild yeast species than the other medium. 


After isolating wild yeasts, we will be identifying the different yeast species by sequencing the internal transcribed spacer (ITS) region.  The ITS region is located between the genes that code for the ribosomal subunits.  Because ribosomes are essential for translation of genes, the ribosomal genes are very well conserved between yeast species.  However, since the ITS region is nonessential, it has diverged between yeast species over time.  By sequencing the ITS region, we will be able to accurately identify the species of the wild yeast we collect in order to observe the species composition as well as the genetic diversity of the wild yeast at Bryn Mawr College.