Tuesday, April 30, 2013
Exhibit Hall
Typical lignocellulose-derived sugar platforms intended for biofuel fermentations contain significant amounts of acetic acid, an inhibitor of yeast growth. In order to isolate or construct yeast strains with increased resistance to acetic acid, it is important to better understand how acetic acid exerts deleterious effects. Here we report that a number of amino acid and pyrimidine auxotrophic mutants of Saccharomyces cerevisiae are more sensitive to growth inhibition by acetic acid than a prototrophic strain. At a concentration of 80 mM acetic acid at pH 4.8, initial uptake of leucine, uracil, lysine, histidine, tryptophan, phosphate, and glucose by a prototrophic strain decreased relative to a non-acetic acid-treated control. We have identified two potential mechanisms by which nutrient uptake may be inhibited by acetic acid. Intracellular ATP levels are severely decreased upon acetic acid treatment, which likely affects ATP-dependent proton symport. In addition, the expression of genes encoding some nutrient transporters was found to be repressed by acetic acid, including HXT1 and HXT2 that encode glucose transporters that operate by facilitated diffusion, not proton symport. In total, these results suggest that compromised nutrient uptake may contribute to growth inhibition by acetic acid.