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Related Concept Videos

Plasmids01:28

Plasmids

Plasmids are extrachromosomal DNA molecules found in bacteria, archaea, and some eukaryotic microbes like yeast. These small, circular DNA structures typically contain fewer than 30 genes, although some may exist linearly. Plasmids vary in their number within a cell, known as copy number. Single-copy plasmids are present in one copy per cell and multi-copy plasmids are present in multiple copies, reaching over 100 copies per cell.Plasmids usually replicate independently of the chromosomal DNA...
Bacterial Toxins01:12

Bacterial Toxins

Bacterial toxins are sophisticated virulence factors that enable pathogenic bacteria to interact with, invade, and damage host tissues. These toxins fall broadly into two types: protein exotoxins, which are secreted into the environment and target specific host receptors, and lipopolysaccharide endotoxins, which are structural components of the bacterial outer membrane released primarily during bacterial lysis or membrane shedding. Exotoxins generally act more selectively, binding to cell...
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DNA Bacteriophages

Bacteriophages, or phages, are viruses that specifically infect bacteria, utilizing their genetic material to hijack host cellular machinery for replication. DNA bacteriophages employ single-stranded DNA (ssDNA) or double-stranded DNA (dsDNA) genomes. These phages exhibit diverse replication strategies and host interactions, influencing their ecological roles and applications in biotechnology and medicine.ssDNA BacteriophagesssDNA phages, with their small genomes, utilize unique strategies to...
Regulation of Bacterial Virulence01:28

Regulation of Bacterial Virulence

Pathogenic bacteria employ a range of regulatory mechanisms to modulate the expression of virulence genes in response to environmental and host-derived signals. These mechanisms ensure that virulence factors are expressed only under favorable conditions, thereby optimizing infection and survival strategies.Mechanisms of Virulence RegulationKey regulatory strategies include:Two-Component Systems: These consist of a membrane-bound sensor kinase and a cytoplasmic response regulator. Environmental...
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Bacterial conjugation is a mechanism of horizontal gene transfer that enables the exchange of genetic material between bacterial cells through direct contact. This process is facilitated by a donor cell carrying a conjugative plasmid, which encodes genes necessary for pilus formation, DNA replication, and transfer. The conjugative plasmid plays a central role in initiating and executing the transfer of genetic material.The tra region of the conjugative plasmid encodes proteins responsible for...
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Related Experiment Video

Updated: May 15, 2026

Purification of a High Molecular Mass Protein in Streptococcus mutans
09:51

Purification of a High Molecular Mass Protein in Streptococcus mutans

Published on: September 14, 2019

Cryptic Streptococcus mutans 5.6-kb plasmids encode a toxin-antitoxin system for plasmid stabilization.

Anke Rheinberg1, Izabela Jadwiga Swierzy, Tuan Dung Nguyen

  • 1Division of Oral Microbiology and Immunology, Department of Operative and Preventive Dentistry & Periodontology, RWTH Aachen University Hospital, Aachen, Germany.

Journal of Oral Microbiology
|January 19, 2013
PubMed
Summary

This study sequenced two Streptococcus mutans plasmids, revealing a novel toxin-antitoxin system (RelBEplas) that may stabilize plasmid transfer. Further research is needed to confirm its role in host survival during stress.

Keywords:
HicBAMazEFRelBEStreptococcus mutansplasmid addiction systemregulator of translationtoxin–antitoxin cassette

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Published on: May 23, 2021

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Streptococcus mutans frequently harbors a 5.6-kb plasmid, but its functions remain largely uncharacterized.
  • Previous knowledge was primarily based on a single plasmid study (pUA140).

Purpose of the Study:

  • To sequence and analyze the genetic organization of two S. mutans 5.6-kb plasmids, pDC09 and pNC101.
  • To identify and characterize novel genes and functional elements within these plasmids.

Main Methods:

  • PicoGreen dsDNA quantification and Real-Time quantitative PCR (RTQ-PCR) for plasmid copy number determination.
  • Open reading frame (ORF) identification and sequence analysis.
  • Bioinformatic analysis including protein sequence identity and structural similarity comparisons (I-Tasser).

Main Results:

  • Plasmid copy number ranged from 10 to 74 depending on the S. mutans strain.
  • Six ORFs were identified, including homologs for Rep and Mob proteins.
  • A novel plasmid-encoded toxin-antitoxin (TA) system, RelBE(plas), was discovered, comprising RelE (toxin) and RelB (antitoxin) homologs.
  • RelBE(plas) showed structural similarity to chromosomal TA systems in S. mutans.

Conclusions:

  • The identified RelBE(plas) system likely contributes to plasmid stabilization by potentially eliminating plasmid-free progeny.
  • While plasmid stabilization was confirmed, the system's role in S. mutans persistence under nutritional stress was not demonstrated in this study.