Use of Multi-parameter Flow Cytometry as Tool to Monitor the Impact of Formic Acid on Saccharomyces carlsbergensis Batch Ethanol Fermentations

The use of lignocellulosic materials as substrate for bioethanol production is considered a cost-effective approach to make the biofuel production process economically sustainable. However, lignocellulosic hydrolysis releases toxic compounds such as weak acids which inhibit microorganism growth and ethanol production. In order to understand the physiological response of Saccharomyces carlsbergensis when fermenting glucose in the presence of formic acid (HF), the yeast growth was monitored by multi-parameter flow cytometry. Cytoplasmic membrane potential decreased as the HF concentration increased and as the yeast culture reached the stationary phase. However, the proportion of cells with permeabilized membrane did not increase with the HF concentration increase. The accumulation of reactive oxygen species was also monitored. Control and fermentations at low HF concentrations (