Isolates were cultured from a Saccharomyces cerevisiae strain evolved to grow and ferment high solids loading of loblolly pine, Pinus taeda, in the presence of inhibitory compounds from a sulfur-dioxide catalyzed steam explosion pretreatment. To assess the phenotypic stability of growth in the presence of inhibitory compounds, the isolates were cultured in rich media with and without the stress of an inhibitory compound cocktail and then inoculated into high solids loading pretreated pine wood fermentations to observe and compare fermentation performance. The result was two divergent profiles in performance: some isolates were able to successfully ferment and produce ethanol in both culturing conditions while other isolates were able to perform only when cultured with the selective pressure of inhibitory compounds. To investigate the factors involved in performance differences, whole transcriptome sequencing was conducted on an isolate from each performance profile for both conditions (with or without inhibitory compounds) in the culturing media. Potentially important genes were identified that could account for the ability to perform in fermentations of high concentrations of pretreated pine wood suggesting changes in metabolic pathways, fatty acid synthesis and degradation, transport, membrane stability, and organelles, along with stress responses.
Keywords: Pine, ethanol, Saccharomyces, inhibitors, transcriptomics