Fermentative production of oligosaccharides by total fermentation utilizing a mixed feedstock
Disclosed are genetically engineered microbial cells for the production of oligosaccharides comprising a galactose-β1,4-glucose moiety at their reducing end, wherein said microbial cells are able to produce said oligosaccharides in the absence of exogenously added lactose, and a method of producing said oligosaccharides using said microbial cells.
1. A genetically engineered microbial cell for the production of lactose or an oligosaccharide of interest which comprises a galactose-β1,4-glucose moiety at its reducing end, wherein said microbial cell is an Escheria coli cell and comprises:
at least one glucose transporter for translocating glucose from the culture medium into the microbial cell's cytoplasm such that free glucose becomes available for intracellular biosynthesis of lactose, wherein the at least one glucose transporter is selected from the group consisting of glucose facilitated diffusion proteins and glucose translocating permeases;
an UDP-galactose biosynthesis pathway comprising the activities of at least a phosphoglucomutase, an UTP-glucose-1-phosphate-uridyltransferase and an UDP-glucose-4-epimerase activity;
at least one β-1,4-galactosyltransferase being able to galactosylate free glucose to intracellularly produce lactose, wherein the β-1,4-galactosyltransferase is encoded by a gene selected from Neisseria meningitidis lgtB, Aggregatibacter aphrophilus lex-1, Pasteurella multocida galTpm 1141; and
wherein the glucokinase gene(s) of the microbial cell have been deleted or functionally inactivated.
2. The genetically engineered microbial cell according to claim 1 , wherein said microbial cell expresses or overexpresses at least one gene encoding the glucose transporter.
3. The genetically engineered microbial cell according to claim 1 , wherein said microbial cell comprises at least one additional glycosyltransferase.
4. The genetically engineered microbial cell according to claim 1 , wherein the microbial cell comprises a glucose-translocating phosphotransferase system.
5. The genetically engineered microbial cell according to claim 1 , wherein said microbial cell further comprises a fructose transporter.
6. The genetically engineered microbial cell according to claim 1 , wherein the microbial cell comprises a fructose specific phosphotransferase system, and wherein the microbial cell further comprises 1-phosphofructokinase.
7. The genetically engineered microbial cell according to claim 5 , wherein said microbial cell comprises fructokinase-6 activity and 6-phosphofructokinase-1 activity.
8. The genetically engineered microbial cell according to claim 6 , wherein the microbial cell comprises a fructose-1,6-bisphosphatase.
9. The genetically engineered microbial cell according to claim 6 , wherein said microbial cell comprises a deletion or functional inactivation of its glucose-6-phosphate isomerase.
10. The genetically engineered microbial cell according to claim 3 , wherein the additional glycosyltransferase is a fucosyltransferase, and wherein said microbial cell comprises a mannose-6-phosphate isomerase, a phosphomannomutase, a mannose-1-phosphate-guanylyltransferase, a GDP-mannose-4,6-dehydratase, and a GDP-L-fucose synthase.
11. The genetically engineered microbial cell according to claim 1 , wherein said microbial cell comprises an exporter protein or a permease exporting the oligosaccharide of interest from the cell.
12. A product comprising a genetically engineered microbial cell according to claim 1 , for production of lactose or an oligosaccharide of interest, wherein the lactose or oligosaccharide of interest comprises a galactose-β1,4-glucose moiety at its reducing end.
13. The genetically engineered microbial cell according to claim 1 , wherein the oligosaccharide of interest is a human milk oligosaccharide selected from 2′-fucosyl-latose, 3-fucosyllactose, 2′,3-difucosyllactose, 3′-sialyllactose, 6′-sialyllactose, 3-fucosyl-3′-sialyllactose, lacto-N-tetraose, lacto-N-neotetraose, lacto-N-fucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N-fucopentaose V, lacto-N-difucosylhexose I, lacto-N-difucosylhexaose II, lacto-N-sialylpentaose LSTa, LSTb, and LSTc.
14. The genetically engineered microbial cell according to claim 2 , wherein the at least one gene encoding the glucose transporter is selected from glf, galP and functional variants thereof.
15. The genetically engineered microbial cell according to claim 3 , wherein the at least one additional glycosyltransferase is selected from fucosyltransferases, sialyltransferases, glucosaminyltransferases, and galactosyltransferases.
16. The genetically engineered microbial cell according to claim 11 , wherein the exporter protein or permease exporting the oligosaccharide of interest from the cell is a sugar efflux transporter.