Exploring the relationship between 1-butanol production and the pseudohyphal response in Saccharomyces cerevisiae

1-butanol is a promising biofuel due to its energy content, ease to apply in current infrastructure, and ability to be used in a series of industrial processes. Butanol is produced naturally by bacteria of the genus Clostridia through the acetone-butanolethanol pathway, but due to the difficulties associated with clostridial fermentations, butanol production in industry-friendly hosts like Saccharomyces cerevisiae is of high interest. Hence, the aim of this project was to assess endogenous 1-butanol production of a filamentous strain of S. cerevisiae and identify potential advantages to the fermentative process found in this genetic background. Endogenous butanol production was induced by deleting the ADH1 gene in a S1278b strain. The resulting mutant displayed altered colony morphology and produced up to 114 ± 19 mg/l of butanol in anaerobic fermentation, more than an adh1d mutant of the W303-1A background. Neither deletions of PDC1 or PDC5 were able to induce butanol accumulation. When the ALD6 and ACS2 genes were overexpressed in the adh1d strains with the aim of reducing intracellular acetaldehyde accumulation, 1-butanol and acetaldehyde accumulation were hindered in the S1278b strain, and completely abolished in the W303-1A strain, suggesting a close relationship between both. RNA-seq analysis of the adh1d and ALD6/ACS2 adh1d strains revealed a correlation between the induction of glutathione biosynthesis genes, and the repression of aerobic respiration and ergosterol biosynthesis with the ability to produce 1-butanol via the endogenous pathways. The results obtained in this project suggest a role for the glutathione-mediated acetaldehyde stress response in facilitating 1-butanol production when ADH1 is deleted, as evidenced by the yields of the S1278b strain. However, further research will be required to better understand how these cellular mechanisms interact and result in accumulation of butanol in S. cerevisiae.