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Applied and Environmental Microbiology, July 2000, p. 2951-2958, Vol. 66, No. 7
Institut für Mikrobiologie, FML
Weihenstephan, Technische Universität München, D-85350
Freising,1 and Institut für
Mikrobiologie, Bundesanstalt für Milchforschung, D-24103
Kiel,2 Germany
Received 27 January 2000/Accepted 17 April 2000
Bacteriophage lysins (Ply), or endolysins, are phage-encoded cell
wall lytic enzymes which are synthesized late during virus multiplication and mediate the release of progeny virions.
Bacteriophages of the pathogen Listeria monocytogenes
encode endolysin enzymes which specifically hydrolyze the cross-linking
peptide bridges in Listeria peptidoglycan. Ply118 is a
30.8-kDa L-alanoyl-D-glutamate peptidase and
Ply511 (36.5 kDa) acts as
N-acetylmuramoyl-L-alanine amidase. In order to
establish dairy starter cultures with biopreservation properties
against L. monocytogenes contaminations, we have introduced ply118 and ply511 into Lactococcus
lactis MG1363 by using a pTRKH2 backbone. The genes were
expressed under control of the lactococcal promoter P32, which proved
superior to other promoters (P21 and P59) tested in this study. High
levels of active enzymes were produced and accumulated in the
cytoplasmic cell fractions but were not released from the cells at
significant levels. Therefore, ply511 was genetically fused
with the SPslpA nucleotide sequence encoding
the Lactobacillus brevis S-layer protein signal peptide. Expression of SPslpA-ply511 from pSL-PL511
resulted in secretion of functional Ply511 enzyme from L. lactis cells. One clone expressed an unusually strong lytic
activity, which was found to be due to a 115-bp deletion that occurred
within the 3'-end coding sequence of
SPslpA-ply511, which caused a frameshift
mutation and generated a stop codon. Surprisingly, the resulting
carboxy-terminal deletion of 80 amino acids in the truncated
Ply511
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Gene Cloning and Expression and Secretion of
Listeria monocytogenes Bacteriophage-Lytic Enzymes in
Lactococcus lactis
(S262-K341) mutant polypeptide strongly increased its lytic
activity. Proteolytic processing of the secretion competent
SPSlpA-Ply511 propeptide following membrane translocation
had no influence on enzyme activity. Immunoblotting experiments using
both cytoplasmic and supernatant fractions indicated that the enzyme
was quantitatively exported from the cells and secreted into the
surrounding medium, where it caused rapid lysis of L. monocytogenes cells. Moreover, transformation of pSL-PL511
C into L. lactis Bu2-129, a lactose-utilizing strain that can
be employed for fermentation of milk, also resulted in secretion of
functional enzyme and showed that the vector is compatible with the
native lactococcal plasmids.
*
Corresponding author. Mailing address: Institut
für Mikrobiologie, FML Weihenstephan, Technische
Universität München, Weihenstephaner Berg 3, D-85350
Freising, Germany. Phone: 49-8161-71-3859. Fax: 49-8161-71-4492. E-mail: M.J.Loessner{at}Lrz.tum.de.
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