Microaerobic metabolism of lactate and propionate enhances vitamin B12 production in Propionibacterium freudenreichii

Background: Propionibacterium freudenreichii is used in biotechnological applications to produce vitamin B12. Although cultured mainly in anaerobic conditions, microaerobic conditions can greatly enhance biomass formation in P. freudenreichii. Since B12 yields may be coupled to biomass formation, microaerobic conditions show great potential for increasing B12 yields in P. freudenreichii. Results: Here we show biomass formation increases 2.7 times for P. freudenreichii grown in microaerobic conditions on lactate versus anaerobic conditions (1.87 g/L vs 0.70 g/L). Consumption of lactate in microaerobic conditions resulted first in production of pyruvate, propionate and acetate. When lactate was depleted, pyruvate and propionate were oxidised with a concomitant sixfold increase in the B12 titer compared to anaerobic conditions, showing potential for propionate and pyruvate as carbon sources for B12 production. Consequently, a fed-batch reactor with anaerobically precultured lactate-grown cells was fed propionate in microaerobic conditions resulting in biomass increase and production of B12. Vitamin yields increased from 0.3 μg B12 per mmol lactate in anaerobic conditions to 2.4 μg B12 per mmol lactate and 8.4 μg B12 per mmol propionate in microaerobic conditions. Yield per cell dry weight (CDW) increased from 41 μg per g CDW in anaerobic conditions on lactate to 92 μg per g CDW on lactate and 184 μg per g CDW on propionate in microaerobic conditions. Conclusions: Here we have shown both B12 yield per substrate and per CDW were highest on cells oxidising propionate in microaerobic conditions, showing the potential of propionate for biotechnological production of vitamin B12 by P. freudenreichii.