Abstract
BACKGROUND: Propionibacterium freudenreichii is used in biotechnological applications to produce vitamin B(12). Although cultured mainly in anaerobic conditions, microaerobic conditions can greatly enhance biomass formation in P. freudenreichii. Since B(12) yields may be coupled to biomass formation, microaerobic conditions show great potential for increasing B(12) 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 B(12) titer compared to anaerobic conditions, showing potential for propionate and pyruvate as carbon sources for B(12) 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 B(12). Vitamin yields increased from 0.3 [Formula: see text] B(12) per mmol lactate in anaerobic conditions to 2.4 [Formula: see text] B(12) per mmol lactate and 8.4 [Formula: see text] B(12) per mmol propionate in microaerobic conditions. Yield per cell dry weight (CDW) increased from 41 [Formula: see text] per g CDW in anaerobic conditions on lactate to 92 [Formula: see text] per g CDW on lactate and 184 [Formula: see text] per g CDW on propionate in microaerobic conditions. CONCLUSIONS: Here we have shown both B(12) 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 B(12) by P. freudenreichii.