Expression of the Staphylococcus hyicus lipase in Lactococcus lactis

The extracellular Staphylococcus hyicus lipase was expressed under the cont rol of different promoters in Lactococcus lactis and Bacillus subtilis. Its expression at high and moderate levels is toxic for the former and the lat ter hosts, respectively. In L. lactis, the lipase was expressed at a high l evel, up to 30% of the total cellular proteins, under the control of the in ducible promoter PnisA. About 80% of the lipase remained associated with th e cells. Close to half of this amount remained associated with the inner si de of the cytoplasmic membrane as unprocessed pre-pro-lipase. The other hal f was trapped by the cell wall and partially degraded at the N-terminal end . This result suggests that extracellular proteases degrade the lipase. Sur prisingly, the kinetics and the pattern of lipase degradation were differen t in the two L. lactis subspecies, L. lactis subsp. cremoris and L. lactis subsp. lactis. The extracellular proteolytic systems that degrade lipase ar e thus different in these closely related subspecies. The incorrect export of the lipase is not due to an inappropriate leader peptide but may be due to an inefficiency of several steps of lipase secretion. We propose that (i ) the S. hyicus lipase may require a special accessory system to be correct ly exported or (ii) the kinetics of lipase synthesis may be a critical fact or for proper folding.