Expression of LIP1 and LIP2 genes from Geotrichum species in baker's yeaststrains and their application to the bread-making process

Lipolytic baker's yeast strains able to produce extracellular active lipase have been constructed by transformation with plasmids containing the LIP1 and LIP2 genes from Geotrichum sp. under the control of the Saccharomyces c erevisiae actin promoter (pACT1). Lipase productivity differed between both constructs, YEpACT-LIP1-t and YEpACT-LIP2-t, being higher for the strain b earing the LIP2 gene in all culture media tested. This result appeared not to be the consequence of a defect in the transcription of the LIP1 gene as revealed by Northern blot analysis. Replacing the signal sequence of LIP1 b y that of LIP2 in the YEpACT-LIP1-t plasmid enhanced significantly the secr etion of lipase 1, but the levels of lipase activity were still lower than those found for the YEpACT-LIP2-t transformant. Recombinant lipase 2 protei n produced by baker's yeast exhibited biochemical properties similar to tho se of the natural enzyme. Fermented dough prepared with YEpACT-LIP2-t-carry ing cells rendered a bread with a higher loaf volume and a more uniform cru mb structure than that prepared with control yeast. These effects were stro nger by the addition in the bread dough formulas of a preferment enriched i n recombinant lipase 2.