Allopurinol supplementation of the growth medium enhances the fermentation of lignocellulosic hydrolysates to ethanol by Saccharomyces cerevisiae

To fully harness lignocellulosic sugars as fermentation substrates for the production of biofuels and fine chemicals, the tolerance of fermenting microbes to lignocellulose-derived microbial inhibitory compounds (LDMICs) must be improved. Towards this goal, we exploited the ability of allopurinol, a xanthine dehydrogenase/oxidase inhibitor, to promote purine salvage and nucleic acid biosynthesis to alleviate LDMIC-induced DNA damage, thereby improving the LDMIC tolerance of Saccharomyces cerevisiae NRRL Y-566 during the fermentation of lignocellulosic sugars to ethanol. By supplementing LDMIC-replete wheat straw and corn stover hydrolysates (CSH) with 0.5-8 mM allopurinol, a concentration-dependent increase in ethanol production was observed. Also, by pulse-feeding allopurinol to a model sugar-LDMIC mixture and switching fermentation from aerobic to microaerophilic condition at the exponential growth phase of S. cerevisiae NRRL Y-566, cell growth, ethanol concentration, productivity, and yield improved by 12.0%, 53.1%, 54.0%, and 50.0%, respectively, when compared to the allopurinol-unsupplemented control. Similarly, when 100% (v/v) CSH was used as carbon source, S. cerevisiae NRRL Y-566 growth, ethanol titer, productivity, and yield increased by 19%, 21%, 20% and 24%, respectively. Additionally, allopurinol reduced the onset of stationary growth phase of S. cerevisiae by 12 h and extended its chronological lifespan by 16 h during growth in100% CSH. These results underscore the feasibility of exploiting allopurinol-mediated increase in LDMIC tolerance by S. cerevisiae for the fermentation of lignocellulosic-derived sugars to ethanol.