Abstract
Great amounts of carbon dioxide generated by Pseudomonas denitrificans during high aerobic vitamin B12 fermentation, while the influence of CO2 concentration on vitamin B12 production remains unclear. In this paper, we present parallel experiments to investigate various levels of inlet CO2 fractions on the physiological metabolism of P. denitrificans in laboratory scale fermentation. The results demonstrated that the oxygen transfer rate, cell growth and glucose consumption were inhibited with CO2 fraction elevated from 0.03% to 8.86 ± 0.24%, while the most exciting results showed that the specific vitamin B12 production rate and the yield to glucose were greatly stimulated when dissolved CO2 increased to 8.86 ± 0.24%. Therefore, the optimal exhausted CO2 fraction control strategy in 120 m3 fermenter was established. With the exhaust CO2 concentration was well controlled at 7.5 ± 0.25% on-line, vitamin B12 production greatly improved to 223.7 ± 3.7 mg/L, which was 11.2% higher than that of control. This strategy was proved to be significant necessary and effective for successfully scale up optimization in industrial vitamin B12 fermentation.
Highlights
Vitamin B12 is an important growth factor and has many applications in medicine and nutrition
Researches of Gill and Lacoursiere had revealed that cell growth and metabolism of Pseudomonas fluorescens and Escherichia coli could be stimulated at low dissolved CO2 level not more than 100 mm Hg pressure or 5% inlet gas phase respectively, while it could be greatly inhibited by the increased CO2 concentration [4,5]
Many other reports demonstrated that CO2 could have positive effect on the metabolism of some microorganisms [10], in which existed high CO2fix pathway activity, the anaplerotic reactions were very important for replenishing the metabolites generated from tricarboxylic acid cycle’s pool, Researches had shown that enhanced CO2 could stimulate the activity of key enzymes for the anaplerotic reaction in Corynebacterium glutamicum [11,12] and succinate-producing strain [13] by accelerating the accumulation of glutamate and succinate
Summary
Vitamin B12 is an important growth factor and has many applications in medicine and nutrition. Many other reports demonstrated that CO2 could have positive effect on the metabolism of some microorganisms [10], in which existed high CO2fix pathway activity, the anaplerotic reactions were very important for replenishing the metabolites generated from tricarboxylic acid cycle’s pool, Researches had shown that enhanced CO2 could stimulate the activity of key enzymes for the anaplerotic reaction in Corynebacterium glutamicum [11,12] and succinate-producing strain [13] by accelerating the accumulation of glutamate and succinate The former studies on industrial vitamin B12 fermentation have shown that P. denitrificans has high affinity to oxygen, and accompanied with higher CO2 evolution rate during fermentation [14]. At present, there was not clearly understood of the effect of CO2 on metabolism of vitamin B12 biosynthesis
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