Disclosed are methods for the fermentative production of a sialylated saccharide and genetically engineered microbial cells for use in said method, wherein the genetically engineered microbial cells comprise (i) a sialic acid biosynthesis pathway comprising a glucosamine-6-phosphate N-acetyltransferase, (ii) a cytidine 5'-monophospho- (CMP)-N-acetylneuraminic acid synthetase； and (iii) a sialyltransferase, for producing sialylated saccharides, as well as the use of said sialylated oligosaccharides for providing nutritional compositions.
