The metabolic characteristicsof high-production vitamin B sub(12) by Pseudomonas denitrificans under dissolved oxygen step-wise reduction

BACKGROUND Previous research proved that fermentation via dissolved oxygen (DO) step-wise reduction was favorable for vitamin B sub(12) productivity by Pseudomonas denitrificans , but the high-production mechanism is still unclear. Based on this fact, P. denitrificans metabolic characteristics under different DO supply models were investigated in a 5L fermenter by assaying the activities of the key enzymes involved in central carbon metabolism and the vitamin B sub(12) biosynthetic pathway. RESULTS Compared with fermentation processes under the DO-stat strategy and DO step-wise increase, it was found that DO step-wise reduction for P. denitrificans fermentation could significantly strengthen the Embden-Meyerhof-Parnas flux and weaken the tricarboxylic acid cycle and hexose monophosphate pathway, but also facilitate the activities of delta -aminolevulinic acid synthase and porphobilinogen synthase. CONCLUSIONS When P. denitrificans fermentation was implemented using DO step-wise reduction, the metabolic characteristics indicated that more precursors for vitamin B sub(12) biosynthesis could be generated. As a result, a significant improvement in vitamin B sub(12) productivity was achieved (69.09 plus or minus 4.48mgL super(-1)). copyright 2013 Society of Chemical Industry