J. Bacteriol., Dec 1995, 7011-7018, Vol 177, No. 24
J Law, G Buist, A Haandrikman, J Kok, G Venema and K Leenhouts
A system for generating chromosomal insertions in lactococci is described.
It is based on the conditional replication of lactococcal pWV01-derived
Ori+ RepA- vector pORI19, containing lacZ alpha and the multiple cloning
site of pUC19. Chromosomal AluI fragments of Lactococcus lactis were cloned
in pORI19 in RepA+ helper strain Escherichia coli EC101. The frequency of
Campbell-type recombinants, following introduction of this plasmid bank
into L. lactis (RepA-), was increased by combining the system with
temperature-sensitive pWV01 derivative pVE6007. Transformation of L. lactis
MG1363 (pVE6007) with the pORI19 bank of lactococcal chromosomal fragments
at the permissive temperature allowed replication of several copies of a
recombinant plasmid from the bank within a cell because of the provision in
trans of RepA-Ts from pVE6007. A temperature shift to 37 degrees C resulted
in loss of pVE6007 and integration of the pORI19 derivatives at high
frequencies. A bank of lactococcal mutants was made in this way and
successfully screened for the presence of two mutations: one in the
monocistronic 1.3-kb peptidoglycan hydrolase gene (acmA) and one in the
hitherto uncharacterized maltose fermentation pathway. Reintroduction of
pVE6007 into the Mal- mutant at 30 degrees C resulted in excision of the
integrated plasmid and restoration of the ability of ferment maltose. The
integration plasmid (pMAL) was rescued by using the isolated plasmid
content of a restored Mal+ colony to transform E. coli EC101. Nucleotide
sequencing of the 564-bp chromosomal fragment in pMAL revealed an internal
part of an open reading frame of which the translated product showed
significant homology with ATP-binding proteins MalK of E. coli, Salmonella
typhimurium, and Enterobacter aerogenes and MsmK of Streptococcus mutans.
This combined use of two types of conditional replicating pWV01-derived
vectors represents a novel, powerful tool for chromosomal gene
inactivation, targeting, cloning, and sequencing of the labelled gene.
Copyright © 1995, American Society for Microbiology
A system to generate chromosomal mutations in Lactococcus lactis which allows fast analysis of targeted genes
Department of Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.
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