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Plasmid heterogeneity in Streptococcus cremoris M12R: effects on proteolytic activity and host-dependent phage
Abstract:
Examination of single colony isolates from a culture of Streptococcus cremoris M12R revealed a high degree of variability in plasmid deoxyribonucleic acid composition. Fifty percent of the M12R population displayed proteolytic activity and harbored a 13-Mdalton plasmid (pLR2013). This plasmid was not present in proteinase-deficient variants isolated from the culture, which provided correlative evidence for linkage of proteinase activity to pLR2013. Four percent of the M12R population demonstrated resistance to phage m12r X M12. This resistance was identified by restriction and modification activities against m12r X M12 phage, which was dependent on the presence of a 20-Md plasmid, pLR1020. Loss of restriction and modification activities was observed upon curing of pLR1020. In conjugal mating studies with Streptococcus lactis ME2, transfer frequency of lactose-fermenting ability to a restriction and modification-deficient variant of M12R was 10(2)-fold higher than to a variant exhibiting restriction and modification activities. The data provided evidence for restriction and modification activities in select S. cremoris M12R variants that are linked to pLR1020 and restrict both the plaquing ability of phage and efficiency of plasmid transfer by conjugation.
Insights
Streptococcus cremoris M12R exhibits plasmid variability. A 13-Mdalton plasmid (pLR2013) is linked to proteolytic activity, while a 20-Md plasmid (pLR1020) confers phage resistance and impacts conjugation efficiency.
Area of Science:
- Microbiology
- Molecular Biology
- Bacteriology
Background:
- Streptococcus cremoris M12R displays significant genetic heterogeneity.
- Plasmids are known to carry accessory genes influencing bacterial traits.
Purpose of the Study:
- To investigate the genetic basis of proteolytic activity and phage resistance in S. cremoris M12R.
- To determine the role of specific plasmids in these phenotypic variations.
Main Methods:
- Isolation and characterization of single colony variants.
- Plasmid DNA analysis using gel electrophoresis.
- Conjugal mating experiments to assess gene transfer efficiency.
- Phage resistance assays involving restriction and modification.
Main Results:
- Fifty percent of isolates showed proteolytic activity linked to a 13-Mdalton plasmid (pLR2013).
- Four percent of isolates exhibited phage resistance due to a 20-Md plasmid (pLR1020), which mediated restriction and modification.
- The presence of pLR1020 significantly reduced plasmid transfer frequency during conjugation.
Conclusions:
- Plasmid pLR2013 is strongly correlated with proteolytic activity in S. cremoris M12R.
- Plasmid pLR1020 confers a restriction-modification system that protects against phage M12 and hinders conjugal gene transfer.