LAUSR

When lignocellulosic biomass is utilized as a fermentative substrate to produce biochemicals, the presence of a yeast strain that is resistant to inhibitory chemical compounds (ICCs) released from the biomass is essential for success. In this study, Saccharomyces yeast strains obtained from a NBRC yeast culture collection were evaluated in two different media with ICCs that mimic one another but resemble the hydrolysate of real biomass. When this strain was cultured in the presence of these ICCs, cell wall hydrophobicity increased significantly in octane and dropped when the ICCs were depleted, which demonstrated the contribution of cell-surface hydrophobicity as an adaptive response against the ICCs. The cells with the highest cell wall hydrophobicity displayed progressively stronger flocculation, indicating that the F118 strain is resilient under ICC stress. Gene expression perturbation analysis revealed that regulatory Mot3p from the F118 strain was expressed in response to the concentration of ICCs and controlled expression of the ygp1 gene. The Mot3p of the F118 strain features a unique insertion and deletion of nucleotides that encode glutamine or asparagine residues by comparison with the Mot3p of the S288c strain, which used as a control strain in the present study. The cell wall hydrophobicity of the S288c strain was greatly enhanced and became ICC-responsive after gene swapping with the mot3 gene from the F118 strain. The gene-swapped S288c strain was confirmed to be fermenting 6-fold faster than the wild-type strain, producing 14.5 g/L of ethanol from 30 g/L of glucose consumed in 24 h in a medium containing the afore-mentioned ICCs. These modifications to Mot3p in certain locations in its sequence changed the expression of a gene involved in cell wall hydrophobicity control and boosted the flocculation response to ICC stress, allowing for the acquisition of robustness.