A metabolic pathway engineered Escherichia coli strain (superbug) containing one plasmid harboring an artificial gene cluster encoding all the five enzymes in the biosynthetic pathway of Galalpha l,3Lac through galactose metabolism has been developed. The plasmid contains a lambda promoter, a c1857 repressor gene, an ampicillin resistance gene, and a T7 terminator. Each gene was preceded by a Shine - Dalgarno sequence for ribosome binding. In a reaction catalyzed by the recombinant E. coli strain, Galalpha 1,3Lac trisaccharide accumulated at concentrations of 14.2 mM (7.2 gL(-1)) in a reaction mixture containing galactose, glucose, lactose, and a catalytic amount of uridine 5'-diphosphoglucose. This work demonstrates that large-scale synthesis of complex oligosaccharides can be achieved economically and efficiently through a single, biosynthetic pathway engineered microorganism.

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