Understanding Functional Roles of Native Pentose-Specific Transporters for Activating Dormant Pentose Metabolism inYarrowia lipolytica
Authors: Ryu Seunghyun , Trinh Cong T. 
Published: September 2017

Pentoses including xylose and arabinose are the second-most prevalent sugars of lignocellulosic biomass that can be harnessed for biological conversion. AlthoughYarrowia lipolyticahas emerged as a promising industrial microorganism for production of high-value chemicals and biofuels, its native pentose metabolism is poorly understood. Our previous study demonstrated thatY. lipolytica(ATCC MYA-2613) has endogenous enzymes for D-xylose assimilation, but inefficient xylitol dehydrogenase causesY. lipolyticato assimilate xylose poorly. In this study, we investigated the functional roles of native sugar-specific transporters for activating the dormant pentose metabolism inY. lipolytica.By screening a comprehensive set of 16 putative pentose-specific transporters, we identified two candidates, YALI0C04730p and YALI0B00396p, that enhanced xylose assimilation. The engineered mutants YlSR207 and YlSR223, overexpressing YALI0C04730p and YALI0B00396p, respectively, improved xylose assimilation approximately 23% and 50% in comparison to YlSR102, a parent engineered strain overexpressing solely the native xylitol dehydrogenase gene. Further, we activated and elucidated a widely unknown, native L-arabinose-assimilating pathway inY. lipolyticathrough transcriptomic and metabolic analyses. We discovered thatY. lipolyticacan co-consume xylose and arabinose, where arabinose utilization shares transporters and metabolic enzymes of some intermediate steps of the xylose-assimilating pathway. Arabinose assimilation was synergistically enhanced in the presence of xylose while xylose assimilation was competitively inhibited by arabinose. L-arabitol dehydrogenase is the rate-limiting step responsible for poor arabinose utilization inY. lipolytica. Overall, this study sheds light on the cryptic pentose metabolism ofY. lipolyticaand further helps guide strain engineering ofY. lipolyticafor enhanced assimilation of pentose sugars.

IMPORTANCE

The oleaginous yeastYarrowia lipolyticais a promising industrial platform microorganism for production of high-value chemicals and fuels. For decades since its isolation,Y. lipolyticahas often been known to be incapable of assimilating pentose sugars, xylose and arabinose, that are dominantly present in lignocellulosic biomass. Through bioinformatic, transcriptomic and enzymatic studies, we have uncovered the dormant pentose metabolism ofY. lipolytica. Remarkably, unlike most yeast strains that share the same transporters for importing hexose and pentose sugars, we discovered thatY. lipolyticapossess the native pentose-specific transporters. By overexpressing these transporters together with the rate-limiting D-xylitol and L-arabitol dehydrogenases, we activated the dormant pentose metabolism ofY. lipolytica. Overall, this study provides a fundamental understanding of the dormant pentose metabolism ofY. lipolyticaand guides future metabolic engineering ofY. lipolyticafor enhanced conversion of pentose sugars to high-value chemicals and fuels.