Direct lactic acid production from beech wood by transgenic white-rot fungus Phanerochaete sordida YK-624

•Phanerochaete sordida YK-624 acquired lactic acid (LA) fermentation ability by transformation with bacterial ldh.•Knock-down of the endogenous pyruvate decarboxylase-encoding gene improved LA productivity of the ldh transformant.•Consecutive biological delignification and fermentation using a transgenic white-rot fungus provided direct LA production from wood.•Inclusion of exogenous cellulase in the medium significantly improved LA production by the transgenic fungus.

A lactic acid (LA)-producing strain of the hyper-lignin-degrading fungus Phanerochaete sordida YK-624 with the lactate dehydrogenase-encoding gene from Bifidobacterium longum (Blldh) was constructed. When the endogenous pyruvate decarboxylase gene-knocked down and Blldh-expressing transformant was cultured with beech wood meal, the transformant was able to successively delignify and ferment the substrate. Supplementation of calcium carbonate into the culture medium, significantly increased the level of LA accumulation. Direct LA production (at 0.29 g/l) from wood was confirmed, and additional inclusion of exogenous cellulase in this fermentation yielded significant further improvement in LA accumulation (up to 1.44 g/l). This study provides the first report of direct production of LA by fermentation from woody biomass by a single microorganism, and indicates that transgenic white-rot fungi have a potential use for development of simple/easy applications for wood biorefinery.