Metabolic Engineering for Overproduction of Colanic Acid in <i>Escherichia coli</i> Mutant with Short Lipopolysaccharide

Abstract

Colanic acid is a major exopolysaccharide existing in most <i>Enterobacteriaceae</i> when exposed to an extreme environment. Colanic acid possesses excellent physical properties and biological activities, which makes it a candidate in the food and healthcare market. Previous strategies for colanic acid overproduction in <i>E. coli</i> mainly focus on removing the negative regulator on colanic acid biosynthesis or overexpressing the <i>rcsA</i> gene to up-regulate the <i>cps</i> operon. In this study, modifications in metabolic pathways were implemented in <i>E. coli</i> mutant strains with shortened lipopolysaccharides to improve colanic acid production. First, <i>ackA</i> was deleted to remove the byproduct acetate and the effect of accumulated acetyl-phosphate on colanic acid production was investigated. Second, 11 genes responsible for O-antigen synthesis were deleted to reduce its competition for glucose-1-phosphate and UDP-galactose with colanic acid production. Third, <i>uppS</i> was overexpressed to supply lipid carriers for synthesizing a colanic acid repeat unit. Colanic acid production in the final engineered strain WZM008/pTrcS reached 11.68 g/L in a 2.0 L bioreactor, 3.54 times the colanic acid production by the WQM001 strain. The results provide insights for further engineering <i>E. coli</i> to maximize CA production.