Engineering robust yeast for neutralizing-agent-free production of lactic acid from sugarcane bagasse hydrolysate

From a sustainability standpoint, utilizing lignocellulose-based material for lactic acid production is highly advantageous. By-products generated by pre-treatment of biomass, however, tend to exhibit an inhibitory effect on microbial hosts. Supplementation of neutralizing agents also produces harmful waste for the environment. Here, we report a rapid and non-neutralized fermentation by an original strain, Saccharomyces cerevisiae BTCC3. This robust host was metabolically engineered by the double disruption of PDC1/5 and the introduction of L-LDH. Within only 15 h, 51% of glucose from sugarcane bagasse (SCB) hydrolysate was converted to lactic acid (productivity at 1.69 g·L-1·h-1) without neutralizing agent supplementation at any stage of fermentation. Cultivation using YPD medium under similar conditions achieved productivity of 3.68 g·L-1·h-1 and the strain could still generate lactic acid after several glucose-feeding treatment without neutralization. This study is the first report of lactic acid production from SCB using a genetically modified host in a process that requires neither detoxification nor neutralization. Overall, this method offers an alternative to tolerance engineering that involves extensive genetic manipulations.