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Sequence and properties of pIM13, a macrolide-lincosamide-streptogramin B resistance plasmid from Bacillus subtilis
Abstract:
We initiated a study of pIM13, a multicopy, macrolide-lincosamide-streptogramin B (MLS) plasmid first isolated from a strain of Bacillus subtilis and described by Mahler and Halvorson (J. Gen. Microbiol. 120:259-263, 1980). The copy number of this plasmid was about 200 in B. subtilis and 30 in Staphylococcus aureus. The MLS resistance determinant of pIM13 was shown to be highly homologous to ermC, an inducible element on the S. aureus plasmid pE194. The product of the pIM13 determinant was similar in size to that of ermC and immunologically cross-reactive with it. The MLS resistance of pIM13 was expressed constitutively. The complete base sequence of pIM13 is presented. The plasmid consisted of 2,246 base pairs and contained two open reading frames that specified products identified in minicell extracts. One was a protein of 16,000 molecular weight, possibly required for replication. The second was the 29,000-molecular-weight MLS resistance methylase. The regulatory region responsible for ermC inducibility was missing from pIM13, explaining its constitutivity. The remainder of the pIM13 MLS determinant was nearly identical to ermC. The ends of the region of homology between pIM13 and pE194 were associated with hyphenated dyad symmetries. A segment partially homologous to one of these termini on pIM13 and also associated with a dyad was found in pUB110 near the end of a region of homology between that plasmid and pBC16. The entire sequence of pIM13 was highly homologous to that of pE5, an inducible MLS resistance plasmid from S. aureus that differs from pIM13 in copy control.
Insights
This study details the pIM13 plasmid, revealing its MLS resistance mechanism and genetic sequence. The plasmid
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- pIM13 is a multicopy plasmid found in Bacillus subtilis.
- It confers resistance to macrolide-lincosamide-streptogramin B (MLS) antibiotics.
- Its genetic basis and regulation are not fully understood.
Purpose of the Study:
- To elucidate the genetic structure and function of the pIM13 plasmid.
- To characterize the MLS resistance determinant within pIM13.
- To compare pIM13 with related plasmids like pE194 and pE5.
Main Methods:
- DNA sequencing of the pIM13 plasmid.
- Analysis of open reading frames and protein products.
- Comparison of pIM13 sequence with homologous plasmids (ermC, pE194, pE5).
Main Results:
- The complete 2,246 bp sequence of pIM13 was determined.
- Two open reading frames were identified, encoding a putative replication protein and an MLS resistance methylase.
- pIM13's MLS resistance is constitutive due to the absence of the ermC inducibility regulatory region.
- pIM13 shows high homology to ermC and pE5, differing in copy control.
Conclusions:
- The pIM13 plasmid possesses a constitutively expressed MLS resistance determinant.
- Its genetic organization is similar to ermC, with key differences in regulatory elements.
- Understanding pIM13 provides insights into plasmid evolution and antibiotic resistance mechanisms.