Improvement of fermentation performance of Gluconobacter oxydans by combination of enhanced oxygen mass transfer in compressed-oxygen-supplied sealed system and cell-recycle technique

Oxygen supply for microbial cultures is often identified as a limiting factor for aerobic fermentation. Through implementation of an integrated oxygen control strategy, the high oxygen mass transfer rate satisfied cellular metabolic demands. Gluconobacter oxydans NL71 fermentation of xylose to xylonic acid was improved remarkably. Finally, the productivity of xylonic acid from xylose by biooxidation was markedly increased to 32.5 +/- 3.1 g/L/h compared to production levels using conventional laboratory-scale bioreactors. By improving microbial fermentative vitality, we successfully bio-converted 1800 g xylose to 1813 +/- 36 g xylonic acid by combination of a fed-batch addition of xylose substrate as well as a cell-recycling strategy. Bioconversion results demonstrated a highly efficient fermentation model that performs continuous bioreaction, assisting the effort to industrialize microbial xylonic acid production.