Construction and characterization of a Lactococcus lactis strain deficient in intracellular ClpP and extracellular HtrA proteases

Abstract

ALactococcus lactisstrain deficient in both its major proteases, intracellular (ClpP) and extracellular (HtrA), was constructed and characterized. This strain, hereafter calledclpP-htrA, could be obtained only by conjugation between aclpPdonor strain and anhtrArecipient strain in the NZ9000 context, allowing heterologous gene expression under the control of the NICE (nisin-controlled expression) system. TheclpP-htrAdouble mutant showed both higher stress tolerance (e.g. high temperature and ethanol resistance) and higher viability than singleclpPorhtrAmutant strains. In addition, the secretion rate of two heterologous proteins (staphylococcal nuclease Nuc and Nuc-E7) was also higher inclpP-htrAthan in the wild-type strain. This strain should be a useful host for high-level production and quality of stable heterologous proteins.