A plasmid-encoded inactive toxin-antitoxin system MtvT/MtvA regulates plasmid conjugative transfer and bacterial
Meng Li1,2, Hua Guo2, Lecheng Wang1
1Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, Provincial Key Laboratory of Biotechnology, College of Life Sciences, Northwest University, Xi'an, Shaanxi 710069, People's Republic of China.
Abstract:
Plasmid-encoded toxin-antitoxin (TA) systems are known for their role in plasmid maintenance via post-segregational killing. Here, we identified an inactive type II TA system, MtvT/MtvA (MtvTA), encoded on the conjugative plasmid pPAD8 from the clinical Pseudomonas aeruginosa strain PAD8. Despite its annotation as a toxin, MtvT exhibited no detectable toxicity in our assays. Interestingly, the deletion of the MtvTA significantly increased the transfer efficiency of pPAD8 from PAD8 to P. aeruginosa strain PAO1. Functional assays revealed that the MtvTA complex negatively regulates plasmid transfer by binding to the promoters of dot/icm system genes. In addition, pPAD8ΔmtvTA attenuated the pathogenicity of the host strain compared to pPAD8, highlighting a regulatory role for MtvTA in virulence. Mechanistically, the MtvTA complex positively regulates the type III and type VI secretion systems and pyocyanin biosynthesis by directly binding to the promoters of exsA and rsmY/rsmZ and indirectly influencing lasI expression, respectively. These findings provide new insights into the regulatory roles of an inactive plasmid-encoded TA system, expanding our understanding of the interplay between plasmids and their bacterial hosts.
Insights
An inactive plasmid toxin-antitoxin system (MtvTA) in Pseudomonas aeruginosa unexpectedly enhances plasmid transfer and regulates virulence factors. This finding reveals novel roles for TA systems beyond plasmid maintenance.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Plasmid-encoded toxin-antitoxin (TA) systems are crucial for plasmid stability through post-segregational killing.
- The conjugative plasmid pPAD8 from a clinical Pseudomonas aeruginosa strain carries a type II TA system, MtvTA.
Purpose of the Study:
- To investigate the function of the MtvTA system on plasmid pPAD8.
- To elucidate the regulatory roles of MtvTA in plasmid transfer, virulence, and secretion systems.
Main Methods:
- Genetic manipulation (deletion of MtvTA).
- Plasmid transfer efficiency assays.
- Toxicity assays.
- Gene expression analysis (promoter binding studies).
Main Results:
- The MtvTA system, despite being annotated as a toxin, showed no toxicity.
- Deletion of MtvTA significantly increased pPAD8 transfer efficiency.
- MtvTA negatively regulates plasmid transfer by binding to dot/icm gene promoters.
- MtvTA positively regulates type III and VI secretion systems and pyocyanin biosynthesis.
- pPAD8 lacking MtvTA showed attenuated host pathogenicity.
Conclusions:
- The MtvTA system acts as a negative regulator of plasmid transfer and a positive regulator of virulence factors in Pseudomonas aeruginosa.
- Inactive TA systems can possess regulatory functions beyond plasmid maintenance.
- This study expands the understanding of plasmid-host interactions and TA system versatility.
