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Applied and Environmental Microbiology, June 2004, p. 3695-3699, Vol. 70, No. 6
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.6.3695-3699.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Transformation of Leuconostoc carnosum 4010 and Evidence for Natural Competence of the Organism

Søren Helmark,1 Mette E. Hansen,1 Birthe Jelle,2 Kim I. Sørensen,2 and Peter R. Jensen1*

BioCentrum, Technical University of Denmark, DK-2800 Lyngby,1 Chr. Hansen A/S, DK-2970 Hørsholm, Denmark2

Received 26 February 2004/ Accepted 27 February 2004

Plasmid transformation in Leuconostoc carnosum 4010 was analyzed. A successful transformation protocol for L. carnosum was established by modifying an existing protocol for Lactococcus lactis. Several parameters, including the number of generations that the cells had grown at the time of harvest, glycine concentration, the time of incubation for phenotypic expression, and the electrical field strength, were investigated and proved to have influence on the transformation frequency. Electrocompetence was found to be transient and to peak in the early exponential growth phase. Optimized conditions resulted in transformation frequencies of up to 6.7 x 105 transformants per microgram of plasmid DNA. A total of five plasmids in L. carnosum were successfully introduced and maintained. Interestingly, we discovered that DNA uptake was of a frequency of 3 x 10–6 to 19 x 10–6 transformants per CFU in the absence of an applied electrical field. We concluded that L. carnosum is naturally competent.

* Corresponding author. Mailing address: BioCentrum, Technical University of Denmark, Building 301, DK-2800 Lyngby, Denmark. Phone: 45 45252510. Fax: 45 45932809. E-mail: PRJ{at}BioCentrum.DTU.DK.

Applied and Environmental Microbiology, June 2004, p. 3695-3699, Vol. 70, No. 6
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.6.3695-3699.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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