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A triggered-suicide system designed as a defense against bacteriophages
G M Djordjevic1, D J O'Sullivan, S A Walker
1Department of Microbiology, North Carolina State University, Raleigh 27695-7624, USA.
Journal of Bacteriology
|November 14, 1997
Summary
A new bacteriophage defense system for Lactococcus lactis uses a genetic trap to activate a bacterial suicide system upon phage infection. This engineered abortive infection method effectively eliminates phages in fermentation environments.
Area of Science:
- Microbiology
- Molecular Biology
- Bacteriophage Research
Background:
- Bacteriophages pose a significant threat to bacterial cultures, particularly in industrial fermentation processes.
- Existing phage defense mechanisms can be circumvented by evolving phages.
- Controlling phage proliferation is crucial for maintaining the stability and productivity of bacterial fermentations.
Purpose of the Study:
- To develop a novel, genetically engineered bacteriophage protection system for Lactococcus lactis.
- To create a system that triggers bacterial self-destruction upon phage infection, preventing phage propagation.
- To engineer a robust defense against phages, including those that may evolve in fermentation environments.
Main Methods:
- Development of a genetic trap system utilizing a strictly phage-inducible promoter (phi31P) from lytic phage phi31.
- Activation of a bacterial suicide system, the LlaIR+ restriction cassette, lethal to gram-positive bacteria.
- Cloning of the phi31P promoter and LlaIR+ cassette into a high-copy-number plasmid (pTRK414H) in Escherichia coli and Lactococcus lactis.
Main Results:
- The pTRK414H system demonstrated no pre-infection restriction activity in E. coli or L. lactis.
- Phage challenges with phi31 in L. lactis(pTRK414H) resulted in a 10,000-fold reduction in plaque-forming efficiency and a fourfold decrease in burst size.
- Center-of-infection assays showed only 15% of infected cells released progeny phage, and the system inhibited four phi31-derived phages at >10-fold higher levels than phi31.
Conclusions:
- The phi31P/LlaIR+ suicide system represents a genetically engineered form of abortive infection.
- This system effectively traps and eliminates phages by destroying the phage genome and killing the host cell.
- The phage-triggered suicide system design is adaptable for other bacterium-phage combinations using a universal lethal gene and a phage-inducible promoter.