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Plasmid transfer between strains of Pseudomonas aeruginosa on membrane filters attached to river stones
1Department of Applied Biology, University of Wales Institute of Science and Technology, Cardiff, UK.
Abstract:
A naturally occurring mercury-resistance, conjugative plasmid, designated pQM1, was isolated from a bacterial population on the surface of stones from a river using Pseudomonas aeruginosa as a recipient. This was a narrow-host-range plasmid [IncP-13; 165 MDa; Tra+, Hgr, fluorescein mercuric acetater, merbrominr, Phi(E79), UVr] confined to some Pseudomonas spp. It was used to demonstrate transfer between bacteria on stones in laboratory microcosm experiments and in situ. Transfer occurred (3.3 X 10(-1) to 6.8 X 10(-9) per recipient) at all the temperatures used (6-20 degrees C), although frequencies were lower in the cold. Nutrient status also affected transfer frequency, rich conditions promoting transfer. The presence of competing bacteria in the natural epilithon lowered transfer frequencies, but when unscrubbed stones were heat treated, transfer was enhanced, perhaps because of nutrient release from the heated epilithon.
Insights
A mercury-resistance plasmid (pQM1) was transferred between bacteria on river stones. Transfer occurred across temperatures and nutrient conditions, influenced by environmental factors like competing bacteria.
Area of Science:
- Environmental Microbiology
- Plasmid Biology
- Bacterial Conjugation
Background:
- Mercury resistance is a significant environmental concern, often mediated by plasmids.
- Conjugative plasmids facilitate horizontal gene transfer, influencing microbial adaptation.
- Understanding plasmid transfer in natural environments is crucial for predicting microbial evolution.
Purpose of the Study:
- To isolate and characterize a naturally occurring mercury-resistance conjugative plasmid (pQM1).
- To investigate the transfer dynamics of pQM1 between bacteria on river stones.
- To assess the influence of environmental factors on plasmid transfer frequencies.
Main Methods:
- Isolation of pQM1 from river stone bacterial populations using Pseudomonas aeruginosa as a recipient.
- Laboratory microcosm experiments to study plasmid transfer on stones under varying temperatures (6-20°C).
- In situ experiments and analysis of environmental factors (nutrient status, competing bacteria, heat treatment) affecting transfer.
Main Results:
- pQM1, a narrow-host-range plasmid, was successfully isolated and characterized.
- Plasmid transfer occurred across all tested temperatures, with reduced frequency at lower temperatures.
- Rich nutrient conditions enhanced transfer, while competing epilithic bacteria reduced it; heat treatment of stones increased transfer.
Conclusions:
- Environmental conditions significantly impact the conjugative transfer of mercury-resistance plasmids in situ.
- pQM1 demonstrates efficient transfer in natural settings, highlighting the role of plasmids in mercury resistance dissemination.
- Findings provide insights into the ecological dynamics of antibiotic resistance gene spread in aquatic environments.
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