Biosynthesis of human milk oligosaccharides in engineered bacteria

An isolated E. coli bacterium comprising

• (i) an exogenous β-galactosidase encoded by an engineered β-galactosidase gene insert, said E. coli comprising a detectable level of β-galactosidase activity that is reduced compared to that of a wild-type E. coli bacterium, wherein the level of β-galactosidase activity comprises between 0.05 and 200 units;
• (ii) an inactivating mutation in a colanic acid synthesis gene;
• (iii) an exogenous fucosyltransferase gene;
• and
• (iv) a functional lactose permease gene,
• wherein the endogenous LacZ gene of said E. coli is deleted or functionally inactivated.