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Transfer and expression of a multiple antibiotic resistance plasmid in marine bacteria
S Chandrasekaran1, B Venkatesh, D Lalithakumari
1Environmental Biotechnology Programme, Centre for Advanced Studies in Botany, University of Madras, Guindy Campus, Madras 600 025, India.
Abstract:
Conjugal transfer of a multiresistance plasmid from Pseudomonas fluorescens to halophilic and halotolerant bacteria was studied under in vitro and in situ conditions. Mating conducted in broth as well as on plates yielded a plasmid transfer frequency of as high as 10(-3). Among these two, plate mating facilitated conjugal transfer of plasmid, because the cell-to-cell contact is more in plate mating. When P. fluorescens was incubated in seawater, the organism progressively lost its colony forming activity within 15 days. Microscopic examination revealed the presence of very short rods, indicating that the cells have become viable but nonculturable (VNC). Mating conducted in natural seawater without any added nutrients revealed that the conjugal transfer is influenced by the physical state of the donor and the recipients as well as the availability of nutrients. But a plasmid transfer frequency of 10(-7) was obtained even after the donor cells have become VNC suggesting that the nonculturable state and nutrient deprived condition may not limit plasmid transfer. The results suggest that the terrestrial bacteria entering into the seawaters with antibiotic resistance plasmids may be responsible for the prevalence of resistance genes in the marine environment.
Insights
Terrestrial bacteria can transfer antibiotic resistance plasmids to marine bacteria, even when the donor cells are nonculturable. This process contributes to the spread of resistance genes in marine environments.
Area of Science:
- Microbiology
- Environmental Science
- Genetics
Background:
- Antibiotic resistance plasmids can be transferred between bacteria.
- Terrestrial bacteria may enter marine environments and interact with marine bacteria.
Purpose of the Study:
- To investigate the conjugal transfer of multiresistance plasmids from *Pseudomonas fluorescens* to marine bacteria.
- To assess the impact of in vitro and in situ conditions on plasmid transfer frequency.
- To determine if viable but nonculturable (VNC) states affect plasmid transfer.
Main Methods:
- Conjugal mating experiments were performed in broth and on plates.
- Donor bacteria (*P. fluorescens*) were incubated in natural seawater to induce a viable but nonculturable (VNC) state.
- Plasmid transfer frequency was quantified under various conditions, including nutrient-deprived and VNC states.
Main Results:
- High plasmid transfer frequencies (up to 10^-3) were observed in vitro, with plate mating being more effective.
- Incubation in seawater induced a viable but nonculturable (VNC) state in *P. fluorescens*.
- Plasmid transfer occurred even when donor cells were in a VNC state and in nutrient-deprived conditions, with frequencies up to 10^-7.
Conclusions:
- Conjugal transfer of antibiotic resistance plasmids can occur between terrestrial and marine bacteria.
- The viable but nonculturable (VNC) state and nutrient availability do not necessarily limit plasmid transfer.
- Terrestrial bacteria carrying resistance plasmids may contribute to the prevalence of antibiotic resistance genes in marine ecosystems.