Mechanism of fermentation performance of Zymomonas mobilis under oxygen supply in batch culture

Abstract

The mechanism of the fermentation performance of Zymomonas mobilis against oxygen supply in batch culture was investigated in detail. It was found that the decline in the metabolic activities under high oxygen supply to the broth was due to the inhibition by accumulated acetaldehyde. Acetaldehyde decreased both the maximum specific growth rate ( μ max) and the cell yield ( Y X/S). Accumulation of acetaldehyde started just after the inoculation and its accumulation rate increased with increases in the initial volumetric oxygen transfer coefficient ( k L a 0). The ratio of ethanol to acetaldehyde production was largely affected by the dissolved oxygen concentration level. By changing the oxygen supply to the broth from high to low during the culture, the cells could not recover from the inhibition but the ethanol productivity was recovered. Acetaldehyde also inhibited the specific oxygen consumption rate ( Q 02). However, the Q 02 increased back to its initial level when acetaldehyde was removed. The changes in Q 02 of washed cells were very similar and was neither affected by the k L a 0 value nor by the oxygen concentration. A mechanism of fermentation performance of the strain against oxygen supply was discussed on the basis of the results of various physiological studies.