4. Conclusions
In this study, we demonstrated that an engineered cellobiosefermenting
yeast strain, EJ2, expressing cdt-1 and gh1-1 from N.
crassa is also capable of fermenting lactose. This result suggests
that the cellobiose transporter, CDT-1, can transport lactose and
the -glucosidase, GH1-1, has -galactosidase activity. Additionally,
a faster lactose-fermenting strain, EJ2e8, was obtained through
laboratory evolution of the EJ2 strain on lactose. The improved lactose
fermentation capacity is ascribed to the further increased copy
numbers of cdt-1 and gh1-1, which in turn resulted in improved
cellobiose fermentations. This study provides evidence that our
engineered EJ2e8 yeast strain can be used for the production of
ethanolfromlactose. The EJ2e8 straincould also be exploited for the
production of other non-ethanol fuels and chemicals from lactose
through further metabolic engineering.