Presence of proline has a protective effect on weak acid stressed Saccharomyces cerevisiae

Fermentation of sugars released from lignocellulosic biomass (LCMs) is a sustainable option for the production of bioethanol. LCMs release fermentable hexose sugars and the currently non-fermentable pentose sugars; ethanol yield from lignocellulosic residues is dependent on the efficient conversion of available sugars to ethanol, a side-product of the process is acetic acid production. Presence of acetic acid reduced metabolic output and growth when compared with controls; however, it was observed that incubation with proline had a protective effect, which was proline specific and concentration dependent; the protective effect did not extend to furan or phenolic stressed yeast cells. Proline accumulating strains displayed tolerance to acetic acid when compared with background strains, whereas, strains with a compromised proline metabolism displayed sensitivity. Sensitivity to weak acids appears to be reduced with the addition of proline; proline is an imino acid freely available as a nitrogen source in the aerobic phase of fermentations. Yeast strains with higher intracellular proline concentrations would be desirable for industrial bioethanol fermentations.