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Pseudomonas streptomycin resistance transposon associated with R-plasmid mobilization
Abstract:
Plasmid pMG1 encodes resistance to gentamicin, streptomycin, sulfonamides, and mercuric ions and also mobilizes pRO161, a transfer-deficient plasmid derived from RP1. Upon mobilization, pRO161 acquires streptomycin resistance (Smr) and can subsequently be remobilized by pMG1 at significantly higher frequencies than pRO161 itself. Both the initial acquisition of Smr and the subsequent mobilization of the transfer-deficient plasmid are recA independent: thus, the Smr determinant appears to be located on a transposon, disignated Tn904. Tn904 transposes to a variety of other plasmids, including RP1, FP2, R388, K, pRO1600, and pBR322, and in some cases the acquisition of this transposon accompanied deletions in the target plasmid. When no deletion occurred, target plasmids gained 5.2 kilobase pairs of DNA and new restriction endonuclease cleavage sites for AvaI, BglII, PstI, SmaI, and SstI. Physical analysis of such plasmids showed that the Tn904 termini are inverted repeat DNA sequences of approximately 124 base pairs. After cloning into vector pRO1723, a single site for restriction endonuclease AvaI was identified within the Smr determinant of Tn904. In Escherichia coli, but not in Pseudomonas aeruginosa. Tn904 shows a gene dosage-dependent expression of streptomycin resistance.
Insights
The streptomycin resistance determinant, Tn904, can transpose to other plasmids and confer resistance. This transposon
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- Plasmid pMG1 confers resistance to multiple antibiotics and heavy metals.
- pMG1 can mobilize transfer-deficient plasmids, such as pRO161.
- Mobilization can lead to the acquisition of new genetic traits by the recipient plasmid.
Purpose of the Study:
- To characterize the streptomycin resistance determinant mobilized by plasmid pMG1.
- To investigate the mechanism of acquisition and transfer of streptomycin resistance.
- To determine the genetic and physical properties of the streptomycin resistance element.
Main Methods:
- Plasmid mobilization experiments in Escherichia coli and Pseudomonas aeruginosa.
- Transposition assays to various plasmids.
- Restriction endonuclease digestion and physical mapping of modified plasmids.
- DNA sequence analysis of transposon termini.
Main Results:
- Plasmid pMG1 mobilizes pRO161, conferring streptomycin resistance (Smr) via transposon Tn904.
- Tn904 transposes to diverse plasmids, sometimes causing deletions.
- Tn904 possesses inverted repeat termini and a single AvaI site within the Smr determinant.
- Streptomycin resistance expression is gene dosage-dependent in E. coli.
Conclusions:
- Tn904 is a novel transposon mediating streptomycin resistance.
- The recA-independent transposition and mobilization of Tn904 are significant findings.
- Tn904's characteristics provide insights into plasmid evolution and antibiotic resistance spread.