Integration and Enhancement of 2-Keto-L-Gulonic Acid Synthesis Pathway in Gluconobactero xydans from Ketogulonicigenium vulgare

Abstract:

Vitamin C （VC），as a kind of vitamins and antioxidants，is widely used in pharmaceutical，food，beverage，and feed industries.2-keto-L-gulonic acid （2-KLG） is the precursor of vitamin C. Recently，the two-step fermentation is used as the main route for vitamin C production. However，this route involves three microorganisms and requires an additional second sterilization process，which significantly increases the cost of both raw materials and energy requirement. Therefore，a one-step fermentation process is considered to be more cost-effective and revolutionary in VC industry. In order to overcome the disadvantages of plasmid overexpression，while the plasmid may be lost and need to add antibiotics in medium，the recombinant strain G. oxydans-ss was constructed by integrating sorbose dehydrogenase gene（sdh） and sorbosone dehydrogenase gene（sndh） from K.vulgare WSH-001 into the genome of G.oxydans WSH-003. This recombinant strain produced 37.6 g/L of 2-KLG after 72 h in 1 L fermentor. The overexpression of pyrroloquinolinequinone （PQQ），a cofactor of SDH and SNDH，has increased the yield of 2-KLG up to 44.5 g/L after 84 h. These results indicated the significant progress in vitamin C industry and show the possibility of development of one-step fermentation for 2-KLG production in future.