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Bacteriocin plasmid pMB1 of Enterococcus faecalis: identification of the cell aggregation substance after induction
R Quirantes1, I Martín, E Valdivia
1Departamento de Microbiología, Facultad de Ciencias, Universidad de Granada, Spain.
Abstract:
Strains of Enterococcus faecalis carrying the bacteriocinogenic plasmids pMB1 or pMB1.1 exhibit a clumping response to culture supernatants of different enterococcal strains. Antibodies raised against cells induced by a homologous pheromone recognize two surface proteins of 152 and 72.5 kDa (the second one is possibly the degradation product of the first), respectively. These antigens are very similar to those found in induced cells of E. faecalis OGIRF(pAM211) as shown by the cross-reaction of the immune sera obtained in this work. We propose that the 152-kDa protein corresponds to the aggregation substance coded by plasmids pMB1 and pMB1.1. Moreover, antibodies raised against induced cells are able to block the pheromone-induced clumping response. When the cells induced to form aggregates by pheromones were examined under a scanning electron microscope they showed a surface layer of hairlike structures.
Insights
Bacteriocinogenic plasmids in Enterococcus faecalis induce a clumping response. Antibodies targeting surface proteins block this aggregation, suggesting a 152-kDa aggregation substance encoded by these plasmids.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Genetics
Background:
- Enterococcus faecalis strains with bacteriocinogenic plasmids (pMB1, pMB1.1) show clumping when exposed to specific culture supernatants.
- This aggregation is mediated by surface proteins, indicating a role for plasmid-encoded factors in bacterial interactions.
Purpose of the Study:
- To identify and characterize the surface proteins responsible for pheromone-induced clumping in Enterococcus faecalis.
- To investigate the genetic basis of this aggregation phenomenon, particularly the role of bacteriocinogenic plasmids.
Main Methods:
- Immunization of animals with pheromone-induced Enterococcus faecalis cells to generate specific antibodies.
- Protein analysis using SDS-PAGE and Western blotting to identify and compare surface antigens.
- Scanning electron microscopy to visualize the ultrastructure of induced bacterial cells.
Main Results:
- Antibodies recognized two surface proteins (152 kDa and 72.5 kDa) in induced E. faecalis cells, with the smaller protein potentially being a degradation product.
- These antigens showed cross-reactivity with those from E. faecalis OGIRF(pAM211), suggesting conserved mechanisms.
- The 152-kDa protein is proposed to be the aggregation substance encoded by pMB1 and pMB1.1 plasmids.
- Antibodies effectively blocked the pheromone-induced clumping response.
- Scanning electron microscopy revealed a hairlike surface layer on aggregated cells.
Conclusions:
- The 152-kDa surface protein, encoded by bacteriocinogenic plasmids pMB1 and pMB1.1, mediates pheromone-induced aggregation in Enterococcus faecalis.
- The identified aggregation substance plays a crucial role in bacterial cell-cell interactions and biofilm formation.
- Further research into this aggregation mechanism could inform strategies for controlling E. faecalis infections.