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Plasmid mediated metal and antibiotic resistance in marine Pseudomonas
1Centre for Advanced Studies in Botany, University of Madras, India.
Abstract:
Pseudomonas sp isolated from the Bay of Bengal (Madras coast) contained a single large plasmid (pMR1) of 146 kb. Plasmid curing was not successful with mitomycin C, sodium dodecyl sulfate, acridine orange, nalidixic acid or heat. Transfer of mercury resistance from marine Pseudomonas to Escherichia coli occurred during mixed culture incubation in liquid broth at 10(-4) to 10(-5) ml(-1). However, transconjugants lacked the plasmid pMR1 and lost their ability to resist mercury. Transformation of pMR1 into E. coli competent cells was successful; however, the efficiency of transformation (1.49 x 10(2)Hgr transformants microsgm-1 pMR1 DNA) was low. E. coli transformants containing the plasmid pMR1 conferred inducible resistance to mercury, arsenic and cadmium compounds similar to the parental strain, but with increased expression. The mercury resistant transformants exhibited mercury volatilization activity. A correlation existed between metal and antibiotic resistance in the plasmid pMR1.
Insights
Marine Pseudomonas bacteria from the Bay of Bengal harbor a large plasmid (pMR1) conferring resistance to mercury, arsenic, and cadmium. This mercury resistance can be transferred to E. coli, with transformants showing enhanced metal resistance and volatilization.
Area of Science:
- Environmental microbiology
- Plasmid biology
- Metal resistance mechanisms
Background:
- Marine bacteria harbor diverse genetic elements, including plasmids, which can mediate resistance to environmental stressors.
- The Bay of Bengal is a unique marine ecosystem with potential for novel microbial discoveries.
- Understanding plasmid-mediated resistance is crucial for assessing environmental risks and developing bioremediation strategies.
Purpose of the Study:
- To characterize a large plasmid (pMR1) from a marine Pseudomonas strain isolated from the Bay of Bengal.
- To investigate the transferability and functional expression of metal resistance conferred by pMR1 in a heterologous host (Escherichia coli).
- To explore the relationship between metal resistance and other traits, such as mercury volatilization and antibiotic resistance.
Main Methods:
- Isolation and characterization of a marine Pseudomonas strain and its plasmid (pMR1).
- Plasmid curing attempts using various chemical and physical agents.
- Conjugation experiments for intergeneric gene transfer to Escherichia coli.
- Transformation of pMR1 into competent E. coli cells.
- Assays for metal resistance (mercury, arsenic, cadmium), mercury volatilization, and antibiotic resistance profiling.
Main Results:
- A 146 kb plasmid, pMR1, was identified in the marine Pseudomonas strain.
- Plasmid curing was unsuccessful using standard methods.
- Mercury resistance transfer to E. coli via conjugation was inefficient and did not involve pMR1.
- Successful transformation of pMR1 into E. coli resulted in inducible resistance to mercury, arsenic, and cadmium, with increased expression compared to the parental strain.
- E. coli transformants exhibited mercury volatilization activity.
- A correlation between metal and antibiotic resistance was observed in pMR1.
Conclusions:
- The marine Pseudomonas plasmid pMR1 confers broad-spectrum inducible resistance to mercury, arsenic, and cadmium.
- pMR1 mediates mercury volatilization activity in E. coli.
- The presence of pMR1 suggests a link between metal and antibiotic resistance in this marine bacterium.
- Further research is needed to elucidate the complete genetic makeup and regulatory mechanisms of pMR1.