title: A chloride-inducible gene expression cassette and its use in induced lysis of Lactococcus lactis.
abstract: A chloride-inducible promoter previously isolated from the chromosome of Lactococcus lactis (J. W. Sanders, G. Venema, J. Kok, and K. Leenhouts, Mol. Gen. Genet., in press) was exploited for the inducible expression of homologous and heterologous genes. An expression cassette consisting of the positive-regulator gene gadR, the chloride-inducible promoter Pgad, and the translation initiation signals of gadC was amplified by PCR. The cassette was cloned upstream of Escherichia coli lacZ, the holin-lysin cassette (lytPR) of the lactococcal bacteriophage r1t, and the autolysin gene of L. lactis, acmA. Basal activity of Pgad resulted in a low level of expression of all three proteins. Growth in the presence of 0.5 M NaCl of a strain containing the gadC::lacZ fusion resulted in a 1,500-fold increase of beta-galactosidase activity. The background activity levels of LytPR and AcmA had no deleterious effects on cell growth, but induction of lysin expression by addition of 0.5 M NaCl resulted in inhibition of growth. Lysis was monitored by following the release of the cytoplasmic marker enzyme PepX. Released PepX activity was maximal at 1 day after induction of lytPR expression with 0.1 M NaCl. Induction of acmA expression resulted in slower release of PepX from the cells. The presence of the inducing agent NaCl resulted in the stabilization of osmotically fragile cells.
authors.affiliation: Department of Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.
authors.forename: J W
authors.initials: JW
authors.lastname: Sanders
authors.forename: G
authors.initials: G
authors.lastname: Venema
authors.forename: J
authors.initials: J
authors.lastname: Kok
mesh_terms: D019677:Artificial Gene Fusion; D001435:Bacteriophages / Q000235:genetics; D001483:Base Sequence; D002473:Cell Wall / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D017931:DNA Primers / Q000235:genetics; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005516:Food Microbiology; D005524:Food Technology; D015870:Gene Expression / Q000187:drug effects; D005798:Genes, Bacterial; D005819:Genetic Markers; D013294:Lactococcus lactis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D009996:Osmotic Fragility; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic
chemical_list: D002712:Chlorides; D017931:DNA Primers; D005819:Genetic Markers; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; C098392:PepX dipeptidyl aminopeptidase