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Growth depression of Serratia marcescens by plasmids that belong to incompatibility group P
1Department of Bacteriology, University of Glasgow, Royal Infirmary, Scotland, Great Britain.
Abstract:
The IncP plasmids R702, RP4 and derivative plasmids including RP4::Mu cts were studied in two pigmented strains of Serratia marcescens. Maintenance of these plasmids resulted in reduced pigmentation and the growth rate of colonies was slower than the plasmid-free parent organisms. DNA inserts and deletions in RP4 altered both the pigmentation phenotype and growth rate of S. marcescens transconjugants and was inversely related to the change in molecular weight. The unrelated plasmids R446b and R46, although of comparable size to RP4, produced neither effect and Rts1, more than three times larger than RP4, produced no visible change in pigmentation phenotype and only a minimal decrease in growth rate. Integration of RP4::Mu cts into the Serratia genome restored pigmentation and growth rate to the same level as the plasmid-free parent. Partial induction at 43 degrees C restored the plasmid to a cytoplasmic state in a proportion of surviving colonies which were typically pale and slow growing.
Insights
IncP plasmids like RP4 significantly impact Serratia marcescens, reducing pigmentation and growth rate. Plasmid integration or removal restores these traits, indicating plasmid presence is key to these bacterial changes.
Area of Science:
- Microbiology
- Bacterial Genetics
Background:
- Serratia marcescens is a pigmented bacterium.
- IncP plasmids are a group of conjugative plasmids known for their broad host range.
Purpose of the Study:
- To investigate the effects of IncP plasmids on the pigmentation and growth rate of Serratia marcescens.
- To determine if plasmid size and genetic modifications influence these effects.
Main Methods:
- Introduction of various IncP plasmids (R702, RP4, RP4::Mu cts, R446b, R46, Rts1) into pigmented Serratia marcescens strains.
- Analysis of colony pigmentation and growth rates in transconjugants.
- Assessment of effects of DNA inserts/deletions in RP4 and plasmid integration into the host genome.
Main Results:
- Maintenance of IncP plasmids RP4 and its derivatives reduced S. marcescens pigmentation and growth rate.
- Plasmid molecular weight, influenced by inserts/deletions, inversely correlated with phenotypic changes.
- Unrelated plasmids of similar or larger size had minimal or no effect.
- Integration of RP4::Mu cts into the Serratia genome restored wild-type pigmentation and growth.
Conclusions:
- The presence and characteristics of IncP plasmids significantly alter Serratia marcescens phenotypes.
- Plasmid genetic stability and molecular weight are critical factors influencing bacterial traits.
- Plasmid integration into the host genome can reverse plasmid-induced phenotypic changes.