Reprogramming the Metabolic Network in Kluyveromyces lactis with a Transcriptional Switch for De Novo Lacto-N-biose Synthesis

Lacto-N-biose (LNB) is a member of the human milk oligosaccharide (HMO) family and is synthesized via an enzymatic reaction in vitro with N-acetylglucosamine (GlcNAc) and cofactors. In this study, LNB was synthesized using a cell factory for the first time. First, three modules were constructed in Kluyveromyces lactis for producing LNB from lactose and GlcNAc without the addition of cofactors. Second, a de novo pathway was constructed in K. lactis for producing LNB from lactose without adding GlcNAc. Finally, a transcriptional switch was introduced into K. lactis to reprogram its metabolic network for improving the flux from GlcNAc-6-P to GlcNAc in the de novo pathway. Subsequently, a final LNB yield of 10.41 g/L, similar to the salvage pathway yield, was achieved through the de novo pathway. The engineered K. lactis provides a promising technology platform for the industrial scale production of LNB.