Enhancement of cell growth and glycolic acid production by overexpression of membrane-bound alcohol dehydrogenase in Gluconobacter oxydans DSM 2003

Abstract

Membrane-bound alcohol dehydrogenase (mADH) was overexpressed in Gluconobacter oxydans DSM 2003, and the effects on cell growth and glycolic acid production were investigated. The transcription levels of two terminal ubiquinol oxidases (bo3 and bd) in the respiratory chain of the engineered strain G. oxydans-adhABS were up-regulated by 13.4- and 3.8-fold, respectively, which effectively enhanced the oxygen uptake rate, resulting in higher resistance to acid. The cell biomass of G. oxydans-adhABS could increase by 26%–33% when cultivated in a 7L bioreactor. The activities of other major membrane-bound dehydrogenases were also increased to some extent, particularly membrane-bound aldehyde dehydrogenase (mALDH), which is involved in the catalytic oxidation of aldehydes to the corresponding acids and was 1.26-fold higher. Relying on the advantages of the above, G. oxydans-adhABS could produce 73.3gl−1 glycolic acid after 45h of bioconversion with resting cells, with a molar yield 93.5% and a space-time yield of 1.63gl−1h−1. Glycolic acid production could be further improved by fed-batch fermentation. After 45h of culture, 113.8gl−1 glycolic acid was accumulated, with a molar yield of 92.9% and a space-time yield of 2.53gl−1h−1, which is the highest reported glycolic acid yield to date.