Genetically engineered strains with reduced byproduct formation

A genetically engineered gram-negative bacterial cell comprising:

• a recombinant nucleic acid sequence that encodes a glycosyltransferase, wherein the glycosyltransferase is selected from the group consisting of:
• β-1,3-N-acetyl-glucosaminyltransferase, β-1,3-galactosyltransferase and β-1,4-galactosyltransferase;
• and
• a deleted or dysfunctional endogenous opgB gene or a deleted or dysfunctional endogenous opgE gene,
• wherein the endogenous deleted or dysfunctional opgB gene natively encodes a protein having an amino acid sequence comprising the amino acids of positions 165 to 763 of SEQ ID NO:
• 3 or a protein having an amino acid sequence with at least 95% sequence identity to the amino acids of positions 165 to 763 of SEQ ID NO:
• 3;
• wherein the endogenous deleted or dysfunctional opgE gene natively encodes a protein having an amino acid sequence comprising the amino acid sequence set forth in SEQ ID NO:
• 4, or a protein having an amino acid sequence with at least 95% sequence identity to SEQ ID NO:
• 4;
• wherein the deleted or dysfunctional endogenous opgB gene results in a decreased or total loss of function of phosphoglycerol transferase I and II, and the deleted or dysfunctional endogenous opgE gene results in a decreased or total loss of function of phosphoethanolamine transferase;
• and
• wherein the gram-negative bacterial cell produces one or more heterologous oligosaccharides under fermentative conditions and is selected from the group consisting of:
• Escherichia sp., Klebsiella sp., Salmonella sp. and Shigella sp.