The disclosure is in the technical field of synthetic biology and metabolic engineering. More particularly, the disclosure is in the technical field of metabolically engineered cells and use of the cells in a cultivation or fermentation. The disclosure describes a cell and a method for production of a di- and/or oligosaccharide. The cell comprises a pathway for production of the di- and/or oligosaccharide and is genetically modified for expression and/or overexpression of at least one set of multiple coding DNA sequences wherein the multiple coding DNA sequences within one set differ in nucleotide sequence and each encode a polypeptide, wherein the polypeptides have the same function and/or activity of interest. Furthermore, the disclosure provides for purification of the di- and/or oligosaccharide from the cultivation.

Provided herein are methods for preparing a glycan product containing legionaminic acid moieties and other nonulosonic acids. Also provided herein are legionaminic acid transferase fusion proteins and vaccine compositions containing glycan products prepared according to the described methods.