Wm. Cambourn et al., PLASMIDS WITH HOMOLOGY TO PFX3 AND PCI3340 IN STARTER LACTOCOCCI AND LACTOBACILLI AND ELECTROPORATION OF SELECTED STRAINS WITH THESE VECTORS, International dairy journal, 8(4), 1998, pp. 251-254
An important consideration in the genetic manipulation of lactic acid
bacteria is whether or not strains retain their normal industrial prop
erties after transformation with plasmid DNA. A survey of plasmid type
s in various lactic acid bacteria showed that pE194-type rolling circl
e (RCR) plasmids were present in 24% of 70 commercial Lactococcus lact
is cheese starters but not in any of 38 strains representing nine spec
ies of Lactobacillus. By contrast, theta plasmids showing homology to
the pCI305 rep gene were present in most (though not all) lactococcal
strains and not in any of the lactobacilli. Plasmids not belonging to
either group were also present in some Lc. lactis and Lactobacillus st
rains. Six selected Lc. lactis subsp. cremoris strains were transforma
ble with pFX3 (a 4.5 kb pE194-type rolling circle vector), yet four of
these strains had significantly lower or zero transformation frequenc
ies with pCI3340 (a 5.7 kb pCI305-based theta vector), possibly due to
plasmid incompatibility. However, all transformants maintained full m
ilk-coagulating activity. In addition to Lc. lactis, strains of Lc. ga
rviae, Enterococcus faecalis and Lactobacillus reuteri were able to be
transformed with pCI3340, making this a potentially useful vector for
these species. (C) 1998 Elsevier Science Ltd. All rights reserved.