There is no “I” in yeast: Studying cooperative strategies in complex yeast communities.

The origin of cooperation is a key question in evolutionary biology. We investigate this question by studying the cooperative interaction of secretion of ‘public-good’ proteins in microorganisms, proteins that serve a beneficial function for the entire community. An established model to study this interaction is the yeast invertase, a secreted enzyme that hydrolyzes sucrose into digestible monosaccharides externally. Thus its producer benefits neighboring cells and can also be exploited by ‘cheating’ non-producing cells. While the dynamics of the producer and ‘cheater’ have been studied, real-world organisms often exhibit non-dichotomous, continuously varying levels of cooperation. We are building a large synthetic library containing variants with a range of cooperative strategies, by altering their invertase secretion level. We do so by utilizing an RNA motif recently discovered in our lab that enhances protein secretion, called SECReTE. This enables us to modulate secretion levels without altering its protein sequence.

We will then compete this synthetic library of ~18,000 secretion variants in a competition assay to study the population dynamics in a complex community and reveal evolutionarily stable strategies of cooperation. In a small-scale competition assay between a wild-type strain, a variant with an increased SECReTE signal and a variant with a decreased SECReTE signal, we find the decreased SECReTE variant is able to rescue its growth defect, suggesting the strains are interacting and able to support each other with shared nutrients. In this work, we aim to further understand the dynamics of complex cooperative interactions and expand our knowledge on the recently discovered SECReTE motif.