Consolidated bioprocessing of cassava starch into microbial lipid for biodiesel production by the amylolytic yeast Lipomyces starkeyi

Direct conversion of starch materials into lipid has been rarely reported as most oleaginous species are unable to efficiently produce amylolytic enzymes. Herein, consolidated bioprocessing (CBP) of cassava starch was described efficiently for lipogenesis by Lipomyces starkeyi. Lipid concentration and yield reached 13.99 g/L and 0.187 g/g, respectively, from 75 g/L cassava starch under optimal conditions. The CBP strategy featured zero enzyme cost, simpler process, and higher oleaginicity compared with the separate hydrolysis and fermentation (SHF) strategy. Amylolytic enzymes with α-amylase, maltase and glucoamylase activities were secreted into extracellular space and the amylase activity reached 3.65 U/mL as maximum. The genome of L. starkeyi was sequenced and a small-scale metabolic model was established. The mechanism of starch hydrolysis for lipogenesis by L. starkeyi was estimated accordingly. The estimated biodiesel parameters of the CBP-derived lipid samples indicated high-quality fuel properties. The CBP strategy provides a highly integrated and techno-economic route for starch-to-lipid conversion.