**1. Introduction**

Bacterial chondroitin is a natural capsular component of some pathogenic strains such as the Gram negative *Escherichia coli* K4 [1], *Pasteurella multocida* type F [2,3], and *Avibacterium paragallinarium* [4]. Chondroitin belongs to the glycosaminoglycan (GAG) family which is found in animal extracellular matrices. Unlike in bacteria, animal chondroitin is normally sulfated and several types of chondroitin sulfate have been reported, depending of sulfation patterns [5]. There is a growing interest in the use of bacterial GAG synthases at the academic and industrial levels in order to produce high yield, structurally well-defined and animal contaminant free products. Synthesis can be achieved either chemo-enzymatically using purified enzymes, or through their expression in suitable, harmless, well known recombinant bacteria. For those purposes, it is critical to characterize and understand the behaviour of available enzymes.

Chondroitin synthase (CS) KfoC has been extensively studied and its tri-dimensional structure has been solved [6]. It is composed of a N-terminal domain A1 which catalyses GalNAc transfer, and a C-terminal domain A2 which catalyses GlcA transfer [7]. KfoC is being used in the engineering of bacterial strains to produce chondroitin at industrial scale [8,9]. Several studies addressed catalytic properties and specificity of KfoC regarding nucleotide-sugars and various acceptors [10–12]. However, studies have never been conducted regarding its behaviour in presence of UDP-galactose.

Here, we report the property of KfoC to incorporate galactose in the absence of UDP-GalNAc in vivo. The ability of some degrading enzymes to cut [β3Gal-β4GlcA]<sup>n</sup> polysaccharide we called "chondbiuronan" is also investigated.
