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The complete DNA sequence and analysis of R27, a large IncHI plasmid from Salmonella typhi that is temperature
C K Sherburne1, T D Lawley, M W Gilmour
1Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Canada.
Abstract:
Salmonella typhi, the causative agent of typhoid fever, annually infects 16 million people and kills 600 000 world wide. Plasmid-encoded multiple drug resistance in S. typhi is always encoded by plasmids of incompatibility group H (IncH). The complete DNA sequence of the large temperature-sensitive conjugative plasmid R27, the prototype for the IncHI1 family of plasmids, has been compiled and analyzed. This 180 kb plasmid contains 210 open reading frames (ORFs), of which 14 have been previously identified and 56 exhibit similarity to other plasmid and prokaryotic ORFs. A number of insertion elements were found, including the full Tn 10 transposon, which carries tetracycline resistance genes. Two transfer regions, Tra1 and Tra2, are present, which are separated by a minimum of 64 kb. Homologs of the DNA-binding proteins TlpA and H-NS that act as temperature-regulated repressors in other systems have been located in R27. Sequence analysis of transfer and replication regions supports a mosaic-like structure for R27. The genes responsible for conjugation and plasmid maintenance have been identified and mechanisms responsible for thermosensitive transfer are discussed.
Insights
The R27 plasmid, crucial for Salmonella typhi drug resistance, has had its complete DNA sequence analyzed. This analysis reveals its genetic makeup and mechanisms for thermosensitive transfer, aiding in understanding typhoid fever
Area of Science:
- Genomics
- Microbiology
- Molecular Biology
Background:
- Salmonella typhi causes typhoid fever, infecting millions globally.
- Plasmid-mediated multidrug resistance in S. typhi is linked to incompatibility group H (IncH) plasmids.
- The R27 plasmid is a key example of the IncHI1 family.
Purpose of the Study:
- To determine the complete DNA sequence of the R27 plasmid.
- To analyze its genetic content, including open reading frames (ORFs) and insertion elements.
- To identify genes involved in conjugation, plasmid maintenance, and thermosensitive transfer.
Main Methods:
- DNA sequencing and compilation of the R27 plasmid.
- Bioinformatic analysis of the 180 kb plasmid sequence.
- Identification and characterization of open reading frames (ORFs) and genetic elements.
Main Results:
- The R27 plasmid sequence (180 kb) contains 210 ORFs, with 56 showing similarity to known genes.
- Identified insertion elements, including the Tn 10 transposon conferring tetracycline resistance.
- Located two transfer regions (Tra1, Tra2) and homologs of regulatory proteins TlpA and H-NS.
- Confirmed a mosaic-like structure and identified genes for conjugation and plasmid maintenance.
Conclusions:
- The complete sequence of the R27 plasmid provides a comprehensive genetic map.
- Understanding R27's genetic elements and transfer mechanisms is vital for combating multidrug-resistant Salmonella typhi.
- The study elucidates the genetic basis for thermosensitive transfer in IncHI1 plasmids.