S125: Production of N-acetyl-D-neuraminic acid by whole cell biocatalyst engineering

N-acetyl-D-neuraminic acid (Neu5Ac), a major species of sialic acid, plays important roles in biological, pathological, and immunological recognition processes. The physiochemical properties of Neu5Ac have made it a valuable resource with an increasing demand in both medicine and biotechnology. The resource availability of Neu5Ac is limited and costly which was insufficient in meeting the large demand of the medical and biotechnological industries. To resolve the problems, a whole-cell biocatalyst process for Neu5Ac production was developed. A metabolically engineered Escherichia coli for enhanced production of Neu5Ac was constructed by co-overexpressing genes of N-acetyl-D-glucosamine 2-epimerase (age) and N-acetyl-D-neuraminic acid aldolase (nanA) wherein some genes of competitive metabolic branch were knocked out by the lambda Red system. The engineered Escherichia coli strain was able to produce 150.6 g/liter (486.9mM) Neu5Ac. A productivity of 9.4 g l^-1 h^-1 for Neu5Ac and conversion yield of 60.9% from N-acetyl-D-glucosamine was achieved in 16 h reaction. The whole cell biocatalytic process of Neu5Ac was favorable compared with natural product extraction, chemical synthesis, or even many other biocatalytic processes. At an industrial level of production, this method can serve as a cost-effective resource for Neu5Ac, supplying enough Neu5Ac to meet the continually increasing demands of the medical, biotechnological and scientific communities.