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Novel mercury resistance determinants carried by IncJ plasmids pMERPH and R391
S E Peters1, J L Hobman, P Strike
1Department of Genetics and Microbiology, University of Liverpool, UK.
Abstract:
HgCl2 resistance (Hgr) in a strain of Pseudomonas putrefaciens isolated from the River Mersey was identified as plasmid-borne by its transfer to Escherichia coli in conjugative matings. This plasmid, pMERPH, could not be isolated and was incompatible with the chromosomally integrated IncJ Hgr plasmid R391. pMERPH and R391 both express inducible, narrow-spectrum mercury resistance and detoxify HgCl2 by volatilization. The cloned mer determinants from pMERPH (pSP100) and R391 (pSP200) have very similar restriction maps and express identical polypeptide products. However, these features show distinct differences from those of the Tn501 family of mer determinants. pSP100 and pSP200 failed to hybridize at moderate stringency to merRTPA and merC probes from Tn501 and Tn21, respectively. We conclude that the IncJ mer determinants are only distantly related to that from Tn501 and its closely homologous relatives and that it identifies a novel sequence which is relatively rare in bacteria isolated from natural environments.
Insights
A novel mercury resistance gene sequence was discovered in bacteria from the River Mersey. This IncJ mercury resistance determinant is distinct from previously identified genes and appears rare in natural environments.
Area of Science:
- Environmental microbiology
- Bacterial genetics
- Plasmid biology
Background:
- Mercury resistance (Hgr) is a significant environmental concern.
- Plasmids are key vectors for antibiotic and heavy metal resistance gene dissemination.
- Previous studies have characterized mercury resistance determinants like Tn501.
Purpose of the Study:
- To characterize a novel mercury resistance determinant found on a plasmid in Pseudomonas putrefaciens.
- To compare this novel determinant with known mercury resistance genes.
- To investigate the prevalence of this new determinant in environmental bacteria.
Main Methods:
- Conjugative mating experiments to transfer mercury resistance to Escherichia coli.
- Plasmid incompatibility tests.
- Cloning of mercury resistance determinants (mer) and restriction mapping.
- Analysis of polypeptide products and DNA hybridization.
Main Results:
- Mercury resistance in Pseudomonas putrefaciens was plasmid-borne (pMERPH) and incompatible with IncJ plasmid R391.
- Both plasmids conferred inducible, narrow-spectrum mercury resistance via volatilization.
- Cloned mer determinants (pSP100, pSP200) showed similar restriction maps and polypeptide products but differed from Tn501.
- Hybridization studies indicated distant relatedness to Tn501 and Tn21 mer determinants.
Conclusions:
- The IncJ mercury resistance determinants represent a novel sequence, distantly related to the Tn501 family.
- This novel mercury resistance sequence is relatively rare in bacteria from natural environments.
- Further research is needed to understand the distribution and evolution of this new determinant.