Biotechnological production of chondroitin

1. A process for the preparation of chondroitin from a bacterial capsular polysaccharidic precursor comprising

growing and amplifying a bacterium transformed with multiple copies of an expression cassette comprising a nucleotide sequence encoding an rfaH protein, said rfaH protein-coding sequence comprising the nucleotide sequence of SEQ ID NO: 9, SEQ ID NO: 13 or SEQ ID NO: 20, wherein said bacterium is Escherichia coli , selected from strains: K5, K4, and K30 having as polysaccharide precursor a K5, K4 and K30 capsular polysaccharide, respectively, or said bacterium is Pasteurella multocida ; and wherein said growing and amplifying step comprises a first batch phase, a second fed-batch phase and a microfiltration regimen;

recovering a cell-free concentrated supernatant via ultrafiltration;

hydrolyzing the cell-free concentrated solution; and

recovering said chondroitin from said cell-free concentrated solution.

2. The process according to claim 1 , wherein the bacterium is Escherichia coli strain K4 having as capsular polysaccharide chondroitin fructosylated on position 3 of glucuronic acid residues.

3. The process according to claim 2 , wherein the E. coli K4 strain is selected from the group consisting of: strain having deposit number ATCC 23502 (American Type Culture Collection—USA), strain Bi 8337/41 (International Escherichia Centre—Denmark), strain NCTC 9005 (National Collection of Type Cultures—UK) and strain U1-41 2616 (Freiburg Collection).

4. The process according to claim 1 , wherein said expression cassette comprises chromosomal DNA, plasmid elements or transposable elements.

5. The process according to claim 4 , wherein said plasmid element comprises the nucleotide sequences of SEQ ID NO: 1 and SEQ ID NO: 6.

6. The process according to claim 1 , wherein the expression cassette comprises a constitutive promoter.

7. The process according to claim 1 , wherein bacterial growth and amplification are carried out during said batch phase and wherein, at the end of the batch phase, as nutrients decrease, fermentation is carried on in the fed-batch phase by addition of a nutrient solution.

8. The process according to claim 7 , wherein:

a) the batch phase is carried out for a time ranging from 6 to 8 hours and biomass concentration expressed as wet weight ranges from 0.6 to 1%;

b) the fed batch phase is initiated after 7-8 h of fermentation and is carried out for a time ranging from 6 to 12 hours and biomass concentration expressed as wet weight ranges from 15 to 40gL −1 ;

wherein the fed batch phase b) is integrated with microfiltration and wherein fermentation volume is kept constant by addition of saline with a composition compatible with that used in the fermentation broth.

9. The process according to claim 8 , wherein the microfiltration is carried out with flat configuration membranes or hollow fiber membranes, with a cut-off between 0.1 and 0.5 μm, said membranes operating with a tangential flow of 80-120 L(min·m 2 ) −1 .

10. The process according to claim 9 , wherein the cut-off is between 0.1 and 0.2 μm said membranes operating with a tangential flow of 90-100 L(min·m 2 ) −1 .

11. The process according to claim 1 , further comprising chemically sulfating the recovered chondroitin.