A recombinant strain of baker's yeast has been constructed which can assimi
late lactose efficiently. This strain has been designed to allow its propag
ation in whey, the byproduct resulting from cheese-making. The ability to m
etabolize lactose is conferred by the functional expression of two genes fr
om Kluyveromyces lactis, LAC12 and LAC4, which encode a lactose permease an
d a beta-galactosidase, respectively. To make the recombinant strain more a
cceptable for its use in bread-making, the genetic transformation of the ho
st baker's yeast was carried out with linear fragments of DNA of defined se
quence, carrying as the only heterologous material the coding regions of th
e two K. lactis genes. Growth of the new strain on cheese whey affected nei
ther the quality of bread nor the yeast gassing power. The significance of
the newly developed strain is two-fold: it affords a cheap alternative to t
he procedure generally used for the propagation of baker's yeast, and it of
fers a profitable use for cheese whey. Copyright (C) 1999 John Wiley & Sons
, Ltd.