High density fermentation of probiotic E. coli Nissle1917 towards heparosan production, characterization, and modification

Abstract

Heparosan is a naturally occurring non-sulfated glycosaminoglycan. Heparosan serves as the substrate for chemoenzymatic synthesis of biopharmaceutically important heparan sulfate and heparin. Heparosan is biologically inert molecule, non-toxic, and non-immunogenic and these qualities of heparosan make it an ideal drug delivery vehicle. The critical-to-quality (CTQ) attributes for heparosan applications include composition of heparosan, absence of any unnatural moieties, and heparosan molecular weight size and unimodal distribution. Probiotic bacteria E. coli Nissle 1917 (EcN) is a natural producer of heparosan. The current work explores production of EcN heparosan and process parameters that may impact the heparosan CTQ attributes. Results show that EcN could be grown to high cell densities (OD600 160-180) in a chemically defined media. The fermentation process is successfully scaled from 5-L to 100-L bioreactor. The chemical composition of heparosan from EcN was confirmed using nuclear magnetic resonance. Results demonstrate that heparosan molecular weight distribution may be influenced by fermentation and purification conditions. Size exclusion chromatography analysis shows that the heparosan purified from fermentation broth results in bimodal distribution, and cell-free supernatant results in unimodal distribution (average molecular weight 68,000 Da). The yield of EcN-derived heparosan was 3 g/L of cell free supernatant. We further evaluated the application of Nissle 1917 heparosan for chemical modification to prepare N-sulfo heparosan (NSH), the first intermediate precursor for heparin and heparan sulfate. KEY POINTS: • High cell density fermentation, using a chemically defined fermentation media for the growth of probiotic bacteria EcN (E. coli Nissle 1917, a natural producer of heparosan) is reported. • Process parameters towards the production of monodispersed heparosan using probiotic bacteria EcN (Nissle 1917) has been explored and discussed. • The media composition and the protocol (SOPs and batch records) have been successfully transferred to contract manufacturing facilities and industrial partners.