Phages I alpha and I2-2: IncI plasmid-dependent bacteriophages
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Abstract:
Phage I alpha was isolated from sewage from Windhoek, South West Africa. It formed relatively clear plaques about 2 mm in diameter, on sensitive strains of Escherichia coli K12 and Salmonella typhimurium LT2. The phage had an hexagonal outline with a diameter of about 24 nm, contained RNA and was resistant to chloroform. Phage I alpha formed plaques or propagated only on organisms carrying I1 plasmids or the I gamma plasmid R621a. The efficiency of plating was higher on E. coli than on S. typhimurium hosts. The phage adsorbed along the length of shafts of I1 pili. Phage I2-2 was isolated from Pretoria sewage. It was a filamentous virus and individual virions varied considerably in length. Phage I2-2 formed turbid plaques which varied from pin point to about 1 mm in diameter on all hosts. It was resistant to RNAase and sensitive to chloroform. Phage I2-2 had a spectrum of activity limited to strains harbouring I2 plasmids but the adsorption site could not be demonstrated. The phage was not related serologically to phages Ifl or PR64FS.
Insights
Two novel bacteriophages, I alpha and I2-2, were isolated from sewage. Phage I alpha targets Escherichia coli and Salmonella typhimurium with I1 plasmids, while Phage I2-2 infects strains with I2 plasmids, offering insights into phage-host interactions.
Area of Science:
- Microbiology
- Virology
- Bacteriology
Background:
- Bacteriophages (phages) are viruses that infect bacteria and can be specific to certain bacterial strains or plasmids.
- Understanding phage-host interactions is crucial for potential applications in biotechnology and medicine.
Purpose of the Study:
- To isolate and characterize novel bacteriophages from environmental sources.
- To determine the host range, morphology, and adsorption properties of the isolated phages.
Main Methods:
- Isolation of phages from sewage samples.
- Plaque assays to determine host range and efficiency of plating.
- Electron microscopy for phage morphology.
- Resistance assays to chloroform and RNAase.
Main Results:
- Phage I alpha, an RNA phage with hexagonal symmetry, was isolated from Windhoek sewage and infects Escherichia coli and Salmonella typhimurium strains carrying I1 plasmids, adsorbing to I1 pili.
- Phage I2-2, a filamentous DNA phage sensitive to chloroform, was isolated from Pretoria sewage and infects strains with I2 plasmids, though its adsorption site was not identified.
- Both phages exhibited distinct plaque morphologies and host specificities.
Conclusions:
- The characterization of phages I alpha and I2-2 expands the knowledge of phage diversity and their specific interactions with bacterial plasmids.
- These findings contribute to the understanding of phage biology and could inform future phage-based applications.