Dairy liquid waste as substrate to obtain biotechnological chondroitin: A circular economy approach

Microbial polysaccharides have been gaining growing interest often as alternative to animal derived products or as sources of novel features for biotechnological applications. Process production costs, however, are still high. A possible solution to that exploits agri-food and dairy industrial byproducts as fermentation substrates. This approach also reduces the need for cost-intensive disposal treatments for these waste sources and supports green and circular economy policies. Therefore, as for other microbial glucuronic acid-based biopolymers (e.g. hyaluronic acid, alginate), in this perspective, wild type and engineered E. coli K4 were used in this work as cell factories to produce K4 capsular polysaccharide (CPS) from renewable sources. The backbone of the K4 CPS, chondroitin, is the precursor of chondroitin sulfate (CS), a glycosaminoglycan found in animal tissues that is extensively used for curing osteoarthritis and studied for several other emerging biomedical applications. Interestingly, also chondroitin showed promising bioactivity in vitro and in vivo. Due to its high availability from local companies, second cheese whey (SCW), a worldwide copious and polluting liquid waste, was used as fermentation substrate in this work. Results showed that SCW fully supports growth of wild type and recombinant E. coli K4 strains, and demonstrate, for the first time up to date, the production of K4 CPS from liquid waste as proof of principle. Batch processes in 3 L fermenters indicated a 100 % improvement of the polysaccharide yield and allowed the production of 1.1 +/- 0.1 g/L of product from the recombinant strain with very low accumulation of acetic acid, demonstrating that SCW by itself fully supports polysaccharide production.