Direct fermentation of Jerusalem artichoke tuber powder for production of L-lactic acid and D-lactic acid by metabolically engineered Kluyveromyces marxianus

An efficient production system for optically pure L- and D-lactic acid (LA) from Jerusalem artichoke tuber powder (JAP) was developed by metabolic engineering of Kluyveromyces marxianus. To construct LA-producing strains, the ethanol fermentation pathway of K. marxianus was redirected to LA production by disruption of KmPDC1 and expression of L- and D-lactate dehydrogenase (LDH) genes derived from Lactobacillus plantarum under the control of the K. marxianus translation elongation factor 1α promoter. To further increase the LA titer, the L-LA and D-LA consumption pathway of host strains was blocked by deletion of the oxidative LDH genes KmCYB2 and KmDLD1. The recombinant strains produced 130 g/L L-LA and 122 g/L D-LA by direct fermentation from 230 g/L JAP containing 140 g/L inulin, without pretreatment or nutrient supplementation. The conversion efficiency and optical purity were ≫>95% and ≫>99%, respectively. This system using JAP and the inulin-assimilating yeast K. marxianus could lead to a cost-effective process for the production of LA.