Production of oligosaccharides

1. A process for producing a desired oligosaccharide in a host microorganism, wherein the desired oligosaccharide is not naturally occurring in said host microorganism, the process comprising the steps of:

a) cultivating the host microorganism that produces the desired oligosaccharide under conditions and in a fermentation medium suitable for the production of the desired oligosaccharide, thereby producing the desired oligosaccharide and undesired biosynthetic saccharide intermediates, wherein the desired oligosaccharide is a human milk oligosaccharide selected from the group consisting of 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-difucosylhexaose I, Lacto-N-difucosylhexaose II, Lacto-N-sialylpentaose LSTa, LSTb, LSTc, Lacto-N-triose II, Lacto-N-neofucopentaose I, Lacto-N-neofucopentaose V, 6′-Galactosyllactose, 3′-Galactosyllactose, Lacto-N-hexaose, Lacto-N-neohexaose, para-Lacto-N-hexaose, para-Lacto-N-neohexaose, Difucosyl-lacto-N-neohexaose, Fucosyl-lacto-N-sialylpentaose a, Fucosyl-lacto-N-sialylpentaose b, Fucosyl-lacto-N-sialylpentaose c, Disialyl-lacto-N-tetraose, Disialyl-lacto-N-fucopentaose, 3-Fucosyl-6′-sialyllactose, Lacto-N-neodifucohexaose I;

b) directly adding an exogenous beta-galactosidase enzyme to the fermentation medium at the end of the cultivation of a) to degrade unused saccharide substrates and/or undesired biosynthetic saccharide intermediates and/or saccharide side products generated during production of the desired oligosaccharide in step a), and

c) recovering the desired oligosaccharide.

2. The process of claim 1 , further comprising centrifuging the cultivated host microorganism to obtain a supernatant and a host microorganism pellet, and recovering the desired oligosaccharide from the supernatant.

3. The process of claim 1 , wherein the host microorganism is a bacterium or a yeast.

4. The process of claim 3 , wherein the host microorganism is an Escherichia coli strain, a Lactobacillus species, a Corynebacterium glutamicum strain, or a Saccharomyces sp. strain.

5. The process of claim 1 , wherein the host microorganism is a wild-type microorganism modified to overexpress proteins for a galactose catabolic pathway under the control of an inducible promoter.

6. A method for purifying a desired oligosaccharide of interest from a mixture containing the desired oligosaccharide and

a) non-desired oligosaccharides or metabolic saccharide products generated during production of the desired oligosaccharide, and/or

b) unused saccharide substrates used in the production of the desired oligosaccharide,

wherein the desired oligosaccharide is a human milk oligosaccharide selected from the group consisting of 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-difucosylhexaose I, Lacto-N-difucosylhexaose II, Lacto-N-sialylpentaose LSTa, LSTb, LSTc, Lacto-N-triose II, Lacto-N-neofucopentaose I, Lacto-N-neofucopentaose V, 6′-Galactosyllactose, 3′-Galactosyllactose, Lacto-N-hexaose, Lacto-N-neohexaose, para-Lacto-N-hexaose, para-Lacto-N-neohexaose, Difucosyl-lacto-N-neohexaose, Fucosyl-lacto-N-sialylpentaose a, Fucosyl-lacto-N-sialylpentaose b, Fucosyl-lacto-N-sialylpentaose c, Disialyl-lacto-N-tetraose, Disialyl-lacto-N-fucopentaose, 3-Fucosyl-6′-sialyllactose, and Lacto-N-neodifucohexaose I,

the method comprising adding beta-galactosidase to the mixture to degrade the non-desired oligosaccharides or metabolic saccharide products or unused substrates; and recovering the desired oligosaccharide from the mixture.

7. The method of claim 6 , wherein the desired oligosaccharide is produced by in vitro oligosaccharide synthesis, by chemical synthesis, or by combinations thereof.

8. The method of claim 6 , wherein the desired oligosaccharide is a non-naturally occurring oligosaccharide in a host microorganism expressing a beta-galactosidase, and wherein the desired oligosaccharide is produced by a microbial fermentation process in the host microorganism.

9. A process for producing a desired oligosaccharide in a host microorganism, wherein the desired oligosaccharide is not naturally occurring in said host microorganism, the process comprising the steps of:

a) cultivating a host microorganism that can produce the desired oligosaccharide under conditions and in a medium suitable for the production of the desired oligosaccharide, thereby producing the desired oligosaccharide and-undesired biosynthetic saccharide intermediates, wherein the desired oligosaccharide is a human milk oligosaccharide selected from the group consisting of 3-Fucosyllactose, 2′3-Di-fucosyllactose, 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-difucosylhexaose I, Lacto-N-difucosylhexaose II, Lacto-N-sialylpentaose LSTa, LSTb, LSTc, Lacto-N-triose II, Lacto-N-neofucopentaose I, Lacto-N-neofucopentaose V, 6′-Galactosyllactose, 3′-Galactosyllactose, Lacto-N-hexaose, Lacto-N-neohexaose, para-Lacto-N-hexaose, para-Lacto-N-neohexaose, Difucosyl-lacto-N-neohexaose, Fucosyl-lacto-N-sialylpentaose a, Fucosyl-lacto-N-sialylpentaose b, Fucosyl-lacto-N-sialylpentaose c, Disialyl-lacto-N-tetraose, Disialyl-lacto-N-fucopentaose, 3-Fucosyl-6′-sialyllactose, Lacto-N-neodifucohexaose I;

b) externally adding a beta-galactosidase to the medium following production of the desired oligosaccharide in step a) to degrade unused saccharide substrates and/or undesired biosynthetic saccharide intermediates and/or saccharide side products generated during production of the desired oligosaccharide in step a); and

c) recovering the desired oligosaccharide;

wherein the unused saccharide substrate is lactose.

10. The method of claim 1 , wherein the host microorganism does not endogenously produce the beta-galactosidase.

11. The method of claim 9 , wherein the host microorganism does not endogenously produce the beta-galactosidase.