Killer Yeast: Uncovering the evolutionary history and environmental/genetic underliers to the antimicrobial activity of three core metabolic enzymes in Saccharomyces cerevisiae
Authors: Hannah Kania 1,2; Mohammad Siddiq 1,2; Nick Brown 3; Patricia Wittkopp 1,2
Affiliations: 1) Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI; 2) Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI; 3) College of Literature, Science, and the Arts, University of Michigan, Ann Arbor, MI
Keywords: Experimental evolution
Some proteins contribute to multiple functions within a cell, and these functions can vary drastically. The GAPDH homologs in Saccharomyces cerevisiae, TDH1, TDH2, and TDH3, encoding core enzymes used in glycolysis, have been identified as precursors to antimicrobial peptides with which S. cerevisiae uses to kill off other yeast species in mixed culture, synthetic grape juice (SGJ) fermentations. This discovery identifies a novel, secondary function of these metabolic genes that is an intriguing example of co-option.
We aim to better understand the environmental and genetic causes that underlie the propensity of S. cerevisiae to kill other yeast in mixed cultures by characterizing how and when the TDH genes were recruited into fungal warfare. Our experiments seek to uncover environmental factors affecting the antimicrobial phenotype, identify the genetic contributions of each TDH gene to S. cerevisiae fungicidal capabilities, and characterize when the TDH-derived antimicrobial property evolved on the yeast phylogeny. To characterize how environment affects S. cerevisiae fungicidal behavior, we grew wild-type S. cerevisiae and Hanseniaspora guilliermondii, a victim species of S. cerevisiae, in single and mixed cultures in different types of liquid media and quantified their abundance. We find a striking effect of growth environment on antimicrobial activity: in SGJ S. cerevisiae completely kills off its victim species, whereas in YPD S. cerevisiae has virtually no effect and is even outcompeted by H. guilliermondii. To quantify how each TDH gene affects antimicrobial activity, we are performing high resolution flow-cytometry based competition assays with H. guillermondii and engineered strains of S. cerevisiae that lack the TDH genes individually or in combination. We are also competing other species of Saccharomyces yeast against H. guillermondii to determine whether production of the TDH-based antimicrobial peptides is a unique feature of S. cerevisiae or an ancient tool of fungal warfare shared by the Saccharomyces genus.