Formic acid resistance in Saccharomyces cerevisiae strains: the role of SAT4 in a proposed molecular model

Saccharomyces cerevisiae's ability to withstand formic acid, the most impactful weak acid on yeast growth and fermentation commonly encountered in lignocellulosic bioethanol, is decisive towards industrial applications. Nevertheless, the mechanisms of formic acid resistance inS. cerevisiaeremain poorly understood. This study explored the transcriptional and metabolic responses of three strains - two resistant (YI30 and CESPLG05), and the sensitive DSM 70449 - to 4.0 g/L formic acid for defining the first model of formic acid resistance in S. cerevisiae. Resistance was linked to the upregulation of SAT4, a regulator of TRK1, a putative formic acid transporter, and FDH1, which detoxifies formic acid. Upregulation of GPD2 and GPP2 highlighted an adaptive glycerol metabolism that supported osmotic stress adaptation and intracellular NAD+ regeneration. Notably, resistant strains showed significantly lower external glycerol concentrations, indicating a finely tuned glycerol pathway. S. cerevisiae strains YI30 and CESPLG05 demonstrated superior ethanol production, producing 23.64 and 22.65 g/L, respectively, from 50 g/L of glucose. Remarkably, this was accomplished in the presence of 4.0 g/L formic acid, reaching 93 and 89 % of the theoretical, respectively. This study provides novel insights into formic acid resistance in S. cerevisiae, offering potential genes candidates for engineering yeast strains for highly tolerant formic acid phenotypes towards their applications in lignocellulosic bioethanol.