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Sequence analysis and characterization of plasmids from Streptococcus thermophilus
Arnold Geis1, Hassan A M El Demerdash, Knut J Heller
1Federal Dairy Research Centre, Institute for Microbiology, Hermann-Weigmann-Strasse 1, 24103 Kiel, Germany. geis@bafm.de
Plasmid
|June 27, 2003
Summary
Eight Streptococcus thermophilus plasmids were sequenced, revealing diverse replication mechanisms and genes for heat shock proteins and restriction-modification systems. Some plasmids enhance bacterial resistance and phage defense.
Area of Science:
- Microbiology and Molecular Biology
- Bacterial Genetics and Genomics
- Plasmid Biology
Background:
- Streptococcus thermophilus is a key bacterium in dairy fermentation.
- Plasmids play a significant role in bacterial adaptation and evolution.
- Understanding plasmid diversity in S. thermophilus is crucial for genetic manipulation and industrial applications.
Purpose of the Study:
- To determine the nucleotide sequences of eight plasmids from S. thermophilus strains.
- To characterize the genetic content, replication mechanisms, and functional roles of these plasmids.
- To investigate the potential for interspecies replication and biotechnological applications.
Main Methods:
- Plasmid isolation from seven S. thermophilus strains.
- High-throughput nucleotide sequencing of isolated plasmids.
- Bioinformatic analysis to identify open reading frames (ORFs), gene functions, and similarities to known genetic elements.
- Replication studies in heterologous hosts (Lactococcus lactis, Bacillus subtilis).
Main Results:
- Sequencing revealed diverse plasmid types, including rolling circle replicons and those with multiple ORFs.
- Identified genes encoding replication initiation proteins (RepA), small heat shock proteins (sHsp) conferring thermo- and acid resistance, and restriction-modification (R/M) systems.
- Demonstrated functional expression of R/M systems in wild-type strains, correlating with phage resistance.
- Showcased interspecies replication capabilities for several plasmids in L. lactis and B. subtilis, with one plasmid exclusive to S. thermophilus.
Conclusions:
- The sequenced plasmids contribute to S. thermophilus adaptation through mechanisms like enhanced stress resistance and phage defense.
- The characterized replicons offer potential for development of shuttle vectors for genetic engineering in lactic acid bacteria and beyond.
- Plasmid pER1-2 represents a S. thermophilus-specific replicon, highlighting unique genetic elements within this species.