Journal of Bacteriology, October 1998, p. 5285-5290, Vol. 180, No. 20
Microbial Ingredients Section, NIZO Food
Research, Ede, The Netherlands
Received 12 March 1998/Accepted 1 August 1998
We characterized the regions involved in replication and
mobilization of the 40-kb plasmid pNZ4000, encoding exopolysaccharide (EPS) production in Lactococcus lactis NIZO B40. The
plasmid contains four highly conserved replication regions with
homologous rep genes (repB1, repB2,
repB3, and repB4) that belong to the
lactococcal theta replicon family. Subcloning of each replicon
individually showed that all are functional and compatible in L. lactis. Plasmid pNZ4000 and genetically labeled derivatives could
be transferred to different L. lactis strains by
conjugation, and pNZ4000 was shown to be a mobilization plasmid. Two
regions involved in mobilization were identified near two of the
replicons; both included an oriT sequence rich in inverted
repeats. Conjugative mobilization of the nonmobilizable plasmid pNZ124
was promoted by either one of these oriT sequences,
demonstrating their functionality. One oriT sequence was
followed by a mobA gene, coding for a
trans-acting protein, which increased the frequency of
conjugative transfer 100-fold. The predicted MobA protein and the
oriT sequences show protein and nucleotide similarity,
respectively, with the relaxase and with the inverted repeat and
nic site of the oriT from the Escherichia
coli plasmid R64. The presence on pNZ4000 of four functional
replicons, two oriT sequences, and several insertion sequence-like elements strongly suggests that this EPS plasmid is a
naturally occurring cointegrate.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Characterization of Multiple Regions Involved in
Replication and Mobilization of Plasmid pNZ4000 Coding for
Exopolysaccharide Production in Lactococcus
lactis
*
Corresponding author. Mailing address: Microbial
Ingredients Section, NIZO Food Research, Kernhemseweg 2, 6718 ZB Ede,
The Netherlands. Phone: 31-318-659511. Fax: 31-318-650400. E-mail: kranenbu{at}nizo.nl.
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