Enhanced erythritol production by a Snf1-deficient Yarrowia lipolytica strain under nitrogen-enriched fermentation condition

Abstract

Erythritol is a new polyol used as a bulk sweetener in food industries, and the bioconversion of agricultural or industrial wastes to erythritol by Yarrowia lipolytica at high productivity is of great cost-effectiveness. In the Yarrowia-erythritol procedure, erythritol synthesis is triggered only under nitrogen starvation condition (or a high carbon-to-nitrogen ratio, C/N), causing an inefficient product yield and the unavailability of nitrogen-rich wastes. Sucrose non-fermenting protein kinase (Snf1) plays an important role in the nitrogen starvation-triggered process. In this study, a Snf1-deficient strain Y. lipolytica M53-S was obtained, and the calculated carbon source uptake (Qs) and erythritol formation (QEry) rates were respectively increased by 46% and 49% when a lower C/N ratio of 20/1 was imposed on M53-S cells than that during nitrogen limitation (C/N=250/1). Moreover, loss of Snf1 abolished the reliance on high osmotic pressure and supplemental nutrition. Results of qRT-PCR suggested that the metabolic enzymes in M53-S were u P-R egulated at transcriptional level under low C/N ratio. The increased enzyme activitiesf also suggested a carbon overflow into the erythritol biosynthetic pathway. During the scaled-up fermentation process, 72.5g/L of erythritol was produced by M53-S within a greatly shortened period. This work confirms the critical role of Snf1 in coupling between nitrogen starvation and product synthesis, which also presents a new perspective in developing a cost-effective process for efficient production of secondary metabolites from nitrogen-rich wastes.