**6. Metabolic Engineering**

Bacterial cells exhibit a wide diversity of capsular polysaccharides that constitute the cell surface of the outer membrane and that mediate interactions with the environment. The capsules are often composed of GAG-like polymers. The structural similarity of microbial capsular polysaccharides to these biomolecules makes these ideal bacteria candidates for non-animal GAG-derived products. It is true that the capsular polysaccharide of *Escherichia coli* K4, the chondroitin synthase polymerase, KfoC, synthesizes a chondroitinlike polysaccharide. While exploring novel methods and conditions to produce chondroitin via metabolic engineering, Leroux and her colleagues expressed KofC in a recombinant strain of *Escherichia coli* deprived of 4-epimerase activity [19]. They realized that KfoC could polymerize a GalNAc-free polysaccharide, giving rise to a novel GAG that they call chondbiuronan.
