Developing a single-stage continuous process strategy for vitamin B₁₂ production with Propionibacterium freudenreichii

Background: Vitamin B₁₂ is a widely used compound in the feed and food, healthcare and medical industries that can only be produced by fermentation because of the complexity of its chemical synthesis. Besides, the use of Generally Recognized as Safe (GRAS) and Qualified Presumption of Safety (QPS) microorganisms, like Propionibacterium freudenreichii, especially non-GMO wild-type producers, are becoming an interesting alternative in markets where many final consumers have high health and ecological awareness. In this study, the production of vitamin B₁₂ using the Propionibacterium freudenreichii NBRC 12391 wild-type strain was characterized and optimized in shake flasks before assessing several scale-up strategies. Results: Initial results established that: (i) agitation during the early stages of the culture had an inhibitory effect on the volumetric production, (ii) 5,6-dimethylbenzimidazole (DMBI) addition was necessary for vitamin B₁₂ production, and (iii) kinetics of vitamin B₁₂ accumulation were dependent on the induction time when DMBI was added. When scaling up in a bioreactor, both batch and fed-batch bioprocesses proved unsuitable for obtaining high volumetric productivities mainly due to carbon source limitation and propionic acid inhibition, respectively. To overcome these drawbacks, an anaerobic single-phase continuous bioprocess strategy was developed. This culture strategy was maintained stable during more than 5 residence times in two independent cultures, resulting in 5.7-fold increase in terms of volumetric productivity compared to other scale-up strategies. Conclusion: Overall, compared to previously reported strategies aimed to reduce propionic acid inhibition, a less complex anaerobic single-phase continuous and more scalable bioprocess was achieved.