Improved propionic acid and 5,6-dimethylbenzimidazole control strategy for vitamin B12 fermentation by Propionibacterium freudenreichii

• Controlling propionic acid concentration could improve vitamin B12 biosynthesis.
• Feed-back inhibition occurred in intermediate biosynthesis of vitamin B12.
• Vitamin B12 biosynthesis increased upon the addition of DMB.
• Propionic acid and DMB control strategy could improve vitamin B12 biosynthesis.
• Vitamin B12 productivity of 0.59 mg/L/h was obtained by repeated batch fermentation.

An efficient fermentation-strengthening approach was developed to improve the anaerobic production of vitamin B12 by cultivation process optimization with Propionibacterium freudenreichii. The effects of the byproduct propionic acid and the precursor 5,6-dimethylbenzimidazole (DMB) on vitamin B12 biosynthesis were investigated. Byproduct inhibition experiments showed that maintaining propionic acid concentration in broth below 10–20 g/L in the early stage and 20–30 g/L in the late stage can efficiently improve vitamin B12 biosynthesis. Batch fermentation indicated the occurrence of feed-back inhibition in intracellular intermediate biosynthesis. In addition, the incorporation of the precursor DMB depended on the fermentation level of the vitamin B12 intermediate. High vitamin B12 concentration (58.8 mg/L) and production (0.37 mg/g) were obtained with an expanded bed adsorption bioreactor by using the propionic acid and DMB control method. The optimum concentration and production of 59.5 and 0.59 mg/L h for vitamin B12 production were respectively achieved after five continuous batches.