Proteinase PI and lactococcin A genes are located on the largest plasmid in Lactococcus lactis subsp. lactis bv. diacetylactis S50.
Lactococcus lactis subsp. lactis bv. diacetylactis S50 produces a lactococcin A-like bacteriocin named bacteriocin S50, and cell envelope-associated PI-type proteinase activity. This strain harbours 3 small size plasmids: pS6 (6.3 kb), pS7a (7.31 kb), and pS7b (7.27 kb). Plasmid curing using a combination of novobiocin treatment (10 microg.mL-1) and sublethal temperature (40 degrees C) resulted in a very low yield (0.17%) of Prt-, Bac-, Bacs derivatives, which retained all 3 small size resident plasmids. Pulsed-field gel electrophoresis of DNA isolated from the strain S50 and cured derivatives in combination with restriction enzyme analysis and DNA-DNA hybridization revealed that S50 contains 2 additional large plasmids: pS140 (140 kb) and pS80 (80 kb). Conjugation experiments using strain S50 as a donor and various lactococcal recipients resulted in Prt+, Bac+, Bacr transconjugants. Analysis of these transconjugants strongly indicated that plasmid pS140 harbours the prt and bac genes encoding proteinase and bacteriocin production, and immunity to bacteriocin, since each Prt+, Bac+, Bacr tranconjugant contained pS140. Accordingly, none of the Prt-,Bac-, Bacs transconjugants contained this plasmid. pS140 was a self-transmissible conjugative plasmid regardless of the host lactococcal recipient used in the test. Frequency of conjugation of plasmid pS140 did not depend on either the donor or recipient strain.
Institute of Molecular Genetics and Genetic Engineering, Vojvode Stepe 444/a, PO Box 23, 11010 Belgrade, Serbia and Montenegro. lab6@EUnet.yu
Milan
M
Kojic
Ivana
I
Strahinic
Ljubisa
L
Topisirovic
D001430:Bacteriocins / Q000096:biosynthesis / Q000235:genetics*; D003227:Conjugation, Genetic; D005798:Genes, Bacterial; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics*; D007610:Kallikreins / Q000096:biosynthesis / Q000235:genetics*; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism; D010957:Plasmids / Q000235:genetics*
D001430:Bacteriocins; D007527:Isoenzymes; C069325:lactococcin A; D007610:Kallikreins; C083038:proteinase P