Development of Saccharomyces cerevisiae isobutanol production strain from osmotolerant and ethanol-producing industrial isolated yeast

Isobutanol is a promising advanced biofuel alternative to ethanol for advanced biofuels and can be converted into sustainable aviation fuel (SAF) via the alcohol-to-jet (ATJ) process. Recent studies attempted to improve isobutanol production from S. cerevisiae by metabolic engineering; nevertheless, engineered strains, mostly derived from laboratory strains, often encountered difficulties in industrial-scale production. Herein, this present study aims to develop an industrially viable isobutanol-producing strain of S. cerevisiae D3C (isolate G2-3-2, identified in the previous study) with minimal genetic modification. Isolate G2-3-2 was subjected to conventional mutagenesis, resulting in the development of an isobutanol-tolerant strain, IbOH-1. The genomic DNA analysis of IbOH-1 revealed numerous mutations in genes associated with nitrogen starvation response, cell wall biosynthesis and integrity, stress resistance-related amino acid biosynthesis and the HOG pathway, all of which may collectively enhance tolerance to isobutanol toxicity. The BAT1 gene was afterwards knocked out by CRISPR/Cas9 to improve isobutanol yield. The isobutanol production from IbOH-1bat1∆ strain was investigated in both nutrient-rich and nutrient-moderate fermentation media, with particular emphasis on optimizing glucose concentration. The highest concentration of isobutanol attained was 2.016 g/L, utilizing nutrient-moderate yeast nitrogenous base (YNB) fermentation conditions containing 150 g/L of glucose, supplemented with 8 g/L of peptone, 3 g/L of (NH4)2SO4, 1 g/L of KH2PO4, 0.5 g/L of MgSO4·7H2O, and 0.05 g/L of FeSO4·7H2O. This study provides new insights into improving isobutanol production in S. cerevisiae, highlighting its potential applicability in industrial biofuel processes.