Mutants of coliphage BF23 able to propagate on smooth strains of Salmonella Typhimurium

2 pages.Mutants of coliphage BF23 able to propágate on smooth strains of Salmonella typhimuríum. The host range of a bacteriophage can be modified by mutation (and/or recombination) either of the host and/or of the bacteriophage. We have previously reported (MOJICA-A & CHARLES, 1975) that coliphage BF23 was able to propágate on rough strains (mutation of the host) of Salmonella typhimurium (strains with incomplete lipopolysaccharide of the cell wall), and that the sensitivity of rough strains was dependent on the presence of an intact bfe+ gene. Moreover the inability of the phage to propágate on smooth strains was due to failure of the phage to absorb to the bacterial cells. Unmutagenized stocks of phage BF23 contain phage particles at frequencies of the order of 10~9 (this frequency declines with age and can be increased by mutagenesis) that are able to propágate on smooth 5. typhimurium strains. Analysis of several spontaneous phage mutants selected for ability to form plaques on smooth S. typhimurium strains indicated that : 1. These mutants still required an intact bfe+ gene for adsorption. 2. The plaque morphology of the mutants was altered. 3. The phage mutants were unable to propágate on rough strains (either 5. typhimurium or Escherichia coli) because they failed to absorb to this type of cells. 4. Phage mutants reverted to ability to propágate on rough strains at frequencies of about 10~8. Revertants failed to propágate on smooth strains. 5. Mutant phages had a decreased buyoant density in CsCl density gradients (g = 1.540 for wild-type phage and 1.490 for the mutants). Revertants had buoyant densities like the wild type. 6. Electron microscopio observations indicated that the mutants lack the tail structure. The mutation in the phage afTects the tail-head assembly system, or alternately it is a negative regulatory mutation that prevenísSociete Belge de BiochimiePeer reviewe