Fermentative production of oligosaccharides by total fermentation utilizing a mixed feedstock

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.