Functional overexpression of genes involved in erythritol synthesis in the yeast .

BACKGROUND

Erythritol, a four-carbon polyol synthesized by microorganisms as an osmoprotectant, is a natural sweetener produced on an industrial scale for decades. Despite the fact that the yeast has been reported since the 1970s as an erythritol producer, the metabolic pathway of this polyol has never been characterized. It was shown that erythritol synthesis in yeast occurs via the pentose phosphate pathway (PPP). The oleaginous yeast is a good host for converting inexpensive glycerol into a value-added product such as erythritol. Glycerol is a renewable feedstock which is produced on a large scale as a waste product by many branches of industry.

RESULTS

In this study, we functionally overexpressed four genes involved in the pentose phosphate pathway (PPP): gene g encoding transketolase (), gene g encoding transaldolase (), gene g encoding glucose-6-phosphate dehydrogenase (), and gene g encoding 6-phosphogluconate dehydrogenase (). Here, we show that the crucial gene for erythritol synthesis in is transketolase. Overexpression of this gene results in a twofold improvement in erythritol synthesis during a shake-flask experiment (58 g/L). Moreover, overexpression of allows for efficient production of erythritol independently from the supplied dissolved oxygen. Fermentation conducted in a 5-L bioreactor at low agitation results in almost 70% higher titer of erythritol over the control strain.

CONCLUSION

This work presents the importance of the PPP in erythritol synthesis and the feasibility for economic production of erythritol from glycerol by the yeast .