Plasmid associated with diplococcin production in Streptococcus

Area of Science:

• Microbiology
• Bacteriology
• Genetics

Background:

• Diplococcin is a bacteriocin produced by certain strains of Streptococcus cremoris.
• Bacteriocin production can be influenced by genetic factors, including plasmids.
• Understanding gene transfer mechanisms is crucial for strain improvement in dairy starter cultures.

Purpose of the Study:

• To investigate the genetic basis of diplococcin production in Streptococcus cremoris.
• To determine the role of plasmids in the transfer of the diplococcin (Dip+) trait.
• To analyze the efficiency of plasmid-mediated conjugation in S. cremoris.

Main Methods:

• Bacterial conjugation experiments were performed using Streptococcus cremoris 346 (Dip+) as the donor and two plasmid-free S. cremoris strains as recipients.
• Transconjugants were selected and analyzed for the presence of the diplococcin production phenotype (Dip+).
• Plasmid DNA was isolated from donor and transconjugant strains, and plasmid sizes were determined.

Main Results:

• The ability to produce diplococcin (Dip+) was successfully transferred via conjugation from S. cremoris 346 to recipient strains at a high frequency (10(-1) per donor).
• All Dip+ transconjugants acquired a 54-megadalton plasmid.
• Spontaneous loss of this 54-megadalton plasmid resulted in the restoration of the diplococcin-negative (Dip-) phenotype in the transconjugant strains.

Conclusions:

• A 54-megadalton plasmid mediates the production and transfer of diplococcin in Streptococcus cremoris.
• Conjugation is an effective mechanism for transferring the diplococcin trait between S. cremoris strains.
• Plasmid-borne genes are responsible for the diplococcin production phenotype in these strains.