Cloning and over-expression of NAD+-dependent xylitol dehydrogenase (XDH) in thermotolerant Gluconobacter frateurii THD32

Abstract

Gene locus of GOX0865 amplified from Gluconobacter oxydans IFO 12528 was expressed in Escherichia
coli. The result revealed the high activity of NAD-dependent dehydrogenase with xylitol as a substrate indicating
that it encoded for xylitol dehydrogease (XDH). The shuttle vector containing this gene was then constructed and
transformed into thermotolerant G. frateurii THD32 of which two types of membrane-bound dehydrogenases
responsible for D-sorbitol (SLDHs) oxidation was inactivated. The transformants exhibited increasing of the XDH
activity almost 10 times. However, these over-expressed strains showed a slight increase of keto-hexose production
from D-sorbitol and the resulting product was identified as L-sorbose. These results suggested that these strains
may require the effective redox balance. On the other hand, they might prefer to accumulate L-sorbose.