The metabolic mechanism of Saccharomyces cerevisiae in response to formic acid stress was studied by non-targeted metabolomics based on liquid chromatography-mass spectrometry (LC-MS) in this work. The data were analyzed by multivariable statistical methods such as principal component analysis (PCA) and orthogonal partial least squares discriminate analysis (OPLS-DA). Totally 226 significantly differential metabolites (P < 0.05) with a variable importance in the projection (VIP) value greater than 1 were identified in Saccharomyces cerevisiae under formic acid stress, mainly including L-tryptophan, L-glutamine, 5-hydroxyindoleacetic acid, indoleacetaldehyde, L-phenylalanine, L-glutamate, oxidized glutathione, and 5’-phosphoribosyl-N-formylglycinamide. The analysis of differential metabolic pathways showed that formic acid stress may cause reactive oxygen species (ROS) accumulation, inducing oxidative stress and excessive ATP consumption, and ultimately inhibiting yeast cell growth. In addition, by increasing the contents of intracellular aromatic amino acids and slowing down the rate of anabolism of some amino acids and nucleotides to reduce energy consumption, yeast cells could protect themselves, thus contributing to the improvement of their tolerance to formic acid. This study provides a scientific theoretical reference for further research on methods to improve cellular tolerance to acid inhibitors.

To evaluate the toxic effect of formic acid on Saccharomyces cerevisiae GGSF16, the influence of fomic acid at different concentrations on the growth and metabolism of S. cerevisiae were determined. The results showed that formic acid at 1.8 g/L significantly inhibited the growth of yeast cells, reduced ethanol production, and extended cell fermentation cycle. The contents of extracellular nucleic acid, protein and malondialdehyde, and the activity of intracellular hexokinase in the treated cells were 1.4, 1.67, 5.3 and 3.95 (P < 0.05) times as high as those in the control group, respectively. Scanning electron microscopic (SEM) images showed that a large number of wrinkles and cavities appeared on the surface of intact and smooth yeast cells, and that and cell-cell adhesion was observed. Fourier transform infrared spectra demonstrated that formic acid could destroy the cell wall and increase the permeability of the cell membrane, thus leading to the leakage of cellular contents and cell death finally.