The bacteriophage resistance plasmid pTR2030 forms high-molecular-weight multimers in lactococci

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C Hill1, L A Miller, T R Klaenhammer

  • 1Department of Food Science, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh 27695-7625.

Plasmid
|March 1, 1991
PubMed

Insights

Lactococcus lactis ME2 harbors the pTR2030 plasmid, conferring phage resistance through abortive infection and restriction/modification. This plasmid exists as high-molecular-weight multimers in ME2, but as monomers in transconjugants, restoring phage resistance.

Area of Science:

  • Bacteriology
  • Molecular Biology
  • Genetics

Background:

  • Lactococcus lactis is a key bacterium in dairy fermentation.
  • Phage infection poses a significant threat to industrial L. lactis cultures.
  • The pTR2030 plasmid confers phage resistance mechanisms.

Purpose of the Study:

  • To investigate the physical state and location of the pTR2030 plasmid in Lactococcus lactis ME2.
  • To understand the role of pTR2030 in conferring phage resistance.
  • To characterize the high-molecular-weight form of pTR2030.

Main Methods:

  • Plasmid DNA isolation and purification.
  • Cloning of pTR2030-specific probes.
  • DNA hybridization techniques (Southern blotting).
  • Conjugation experiments for plasmid transfer.

Main Results:

  • pTR2030 exists as high-molecular-weight multimers in L. lactis ME2, not as a monomeric plasmid.
  • These multimers are distinct from chromosomal DNA and are lost in phage-sensitive derivatives.
  • Reintroduction of pTR2030 restores phage resistance and can result in either monomeric or multimeric forms.

Conclusions:

  • The pTR2030 plasmid adopts a high-molecular-weight multimeric form within L. lactis ME2.
  • This multimeric state is associated with the phage-insensitive phenotype.
  • pTR2030 exhibits plasticity in its physical form (monomeric or multimeric) upon transfer.

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