Construction of a flocculating yeast for fuel ethanol production

The expression vector pYX212 harboring the flocculation gene FLO1 from S. cerevisiae W303-1A and the G418 resistance gene kanMX was transformed into S. cerevisiae ZWA46. The transformant ZWA46-F2 was obtained and showed strong and stable flocculation ability. Other properties of the recombinant strain were also studied. The results demonstrated that the onset flocculation was in the early-stationary phase, not coincident with glucose depletion in the culture medium. Moreover, the flocculation ability of the transformant showed no difference at initial pH ranging from 2.5 to 6.0, and could achieve the maximum ethanol concentration of 8.6% (vol.) with an ethanol yield on glucose of 89.8% of the theoretical value. The flocculation property of the transformant ZWA46-F2 seemed to have potential application in the fuel ethanol industry due to the easiness to separate and reuse yeast cells.