Observations on abortive infection of Micrococcus lysodeikticus with bacteriophage

Abstract

Screening of ultraviolet irradiated Micrococcus lysodeikticus cultures for phage-resistant mutants yielded strains capable of producing plaques with virulent phage N6 but not with serologically related virulent phage N1. Adsorption tests conducted with a representative strain revealed that the culture was not truly resistant to N1 since this phage was efficiently adsorbed. Adsorption initiated an abortive infection which terminated with complete lysis of the host cells without liberation of infectious phage. An apparent reversal of the abortive infection was observed when the mutant cells were infected simultaneously with both phages. Under such conditions, 50–60% of the infected cells produced infectious phage, and single cell burst experiments showed that nearly every productive cell yielded both parental phage types and two new stable types in which the plaque morphology and host range characteristics were recombined. It was found that the percentage recovery of infectious centers from mixed-infected cells was influenced by the order in which the two phages infected the cells, and by the time interval between infection with the first phage and subsequent infection with the second phage. When cells were infected first with N6, delay of infection with N1 resulted in increased recoveries. When cells were infected first with N1, recoveries fell off at a rate which was exponential with respect to the time of delay in adding N6. During the course of the abortive infection, there was no increase in rate of oxygen uptake and no net synthesis of ribonucleic acid. Deoxyribonucleic acid was synthesized at a considerably higher rate, and the amount produced was two to three times greater than that found with any of the productive infections studied.