Abstract
The genus Saccharomyces currently includes eight species in addition to the model yeast Saccharomyces cerevisiae, most of which can be consistently isolated from tree bark and soil. We recently found sympatric pairs of Saccharomyces species, composed of one cryotolerant and one thermotolerant species in oak bark samples of various geographic origins. In order to contribute to explain the occurrence in sympatry of Saccharomyces species, we screened Saccharomyces genomic data for protein divergence that might be correlated to distinct growth temperature preferences of the species, using the dN/dS ratio as a measure of protein evolution rates and pair-wise species comparisons. In addition to proteins previously implicated in growth at suboptimal temperatures, we found that glycolytic enzymes were among the proteins exhibiting higher than expected divergence when one cryotolerant and one thermotolerant species are compared. By measuring glycolytic fluxes and glycolytic enzymatic activities in different species and at different temperatures, we subsequently show that the unusual divergence of glycolytic genes may be related to divergent evolution of the glycolytic pathway aligning its performance to the growth temperature profiles of the different species. In general, our results support the view that growth temperature preference is a trait that may have undergone divergent selection in the course of ecological speciation in Saccharomyces.
Highlights
The genus Saccharomyces is best known for its most emblematic member, the model and industrial yeast S. cerevisiae, but comprises in addition eight closely related species [1,2,3]
In the same study a similar situation was found for S. paradoxus and S. uvarum which were sympatric in North America
In order to test the hypothesis that temperature plays a key role in the coexistence of the two populations by contributing for niche divergence and opposing competitive exclusion, we set up a series of competition experiments between a pair of sympatric S. cerevisiae (ZP 567) and S. kudriavzevii (ZP 591) strains isolated from the same sample of oak bark in Portugal (Table S1A)
Summary
The genus Saccharomyces is best known for its most emblematic member, the model and industrial yeast S. cerevisiae, but comprises in addition eight closely related species [1,2,3]. In the comparison between S. cerevisiae and S. mikatae, which has intermediate growth temperature preferences (Figure 1) dN/dS ratios of glycolytic genes are generally lower (Table S3). These results led us to put forward the hypothesis that the glycolytic pathway may have been under selective pressure to adapt to the different growth temperature regimes during evolution of Saccharomyces species.
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