Oxygen-enriched fermentation of sodium gluconate by Aspergillus niger and its impact on intracellular metabolic flux distributions.

Abstract

Different concentrations of oxygen-enriched air were utilized for sodium gluconate (SG) fermentation by Aspergillus niger. The fermentation time shortened from 20 to 15.5h due to the increase of volumetric oxygen transfer coefficient (KLa) and the formation of more dispersed mycelia when inlet oxygen concentration ascended from 21 to 32%. According to metabolic flux analysis, during the growth phase, extracellular glucose for SG synthesis accounted for 79.0 and 85.3% with air and oxygen-enriched air (25%), respectively, whereas the proportions were 89.4 and 93.0% in the stationary phase. Intracellular glucose consumption decreased in oxygen-enriched fermentation, as cell respiration was more high-efficiently performed. Metabolic profiling indicated that most intermediates in TCA cycle and EMP pathway had smaller pool sizes in oxygen-enriched fermentations. Moreover, the main by-product of citric acid dramatically decreased from 1.36 to 0.34gL-1 in oxygen-enriched fermentation. And the sodium gluconate yield increased from 0.856 to 0.903molmol-1.