Coupled engineering strategy of CYB2 deletion and ACS1 overexpression improves cellulosic lactic acid production by Saccharomyces cerevisiae

Lactic acid plays a significant role in the food industry as a natural preservative and serves as a platform chemical for the production of biodegradable poly-lactic acid. While its sustainable production through fermentation using cellulosic biomass instead of traditional sugar and starch raw materials shows promise, there remains limited information available on this method. In this study, a xylose-fermenting and lactic acid-tolerant Saccharomyces cerevisiae strain (BK01) was engineered for improved cellulosic lactic acid production using the promising energy crop, kenaf. Specifically, CYB2 was deleted to inhibit lactic acid consumption (BK02), which was further engineered by ACS1 overexpression to remove the cytotoxic acetate derived from cellulosic biomass (BK03). The BK03 produced 3.25-fold more lactic acid from kenaf pulp hydrolysate than the parental strain (BK01). During pH-controlled fermentation, lactic acid production by BK03 reached a titer of 31 g/L and a productivity of 1.30 g/L-h, the highest value reported so far. This is one of the few studies on yeast-based lactic acid production from lignocellulose.