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