Phage X: a plasmid-dependent, broad host range, filamentous bacterial virus

Area of Science:

• Microbiology
• Virology
• Bacteriology

Background:

• Bacteriophages (phages) are viruses that infect bacteria.
• Phages play crucial roles in microbial ecology and evolution.
• Plasmid-mediated resistance and host range are important factors in phage-bacterial interactions.

Purpose of the Study:

• To isolate and characterize a novel bacteriophage (Phage X) from sewage.
• To determine the host range and infectivity of Phage X, particularly in relation to bacterial plasmids.
• To investigate the physical and chemical properties of Phage X.

Main Methods:

• Isolation of bacteriophage from sewage samples.
• Bacteriophage plating assays on various bacterial strains (Escherichia coli, Salmonella typhimurium, Serratia marcescens, Proteus mirabilis, Pseudomonas aeruginosa) with and without specific plasmids.
• Titration of phage infectivity.
• Determination of phage morphology and resistance to physical/chemical agents (ribonuclease, diethyl ether, chloroform).

Main Results:

• Phage X was isolated by plating on Escherichia coli and Salmonella typhimurium strains carrying the R6K plasmid.
• The phage exhibited infectivity on strains carrying R6K plasmid, including Serratia marcescens, but failed to plaque on Proteus species, despite multiplication.
• Phage X showed infectivity on E. coli and S. typhimurium strains with various other plasmids (groups M, N, P-1, U, W, R775) and adsorbed to pili of Pseudomonas aeruginosa.
• Phage X is filamentous, curly, ribonuclease-resistant, diethyl ether-resistant, and chloroform-sensitive.

Conclusions:

• Phage X possesses a broad host range, primarily determined by the presence of specific bacterial plasmids.
• The phage's ability to adsorb to pili suggests a mechanism of host recognition and attachment.
• Characterization reveals Phage X as a unique filamentous phage with distinct resistance properties.