title: Physiological and genetic aspects of abortive infection of a Shigella sonnei strain by coliphage T7.
abstract: Phage T7 adsorbed to and lysed cells of Shigella sonnei D(2) 371-48, although the average burst size was only 0.1 phage per cell (abortive infection). No mechanism of host-controlled modification was involved. Upon infection, T7 rapidly degraded host deoxyribonucleic acid (DNA) to acid-soluble material. Phage-directed DNA synthesis was initiated normally, but after a few minutes the pool of phage DNA, including the parental DNA, was degraded. Addition of chloramphenicol, at the time of phage infection, prevented both the initiation of phage-directed DNA synthesis and the degradation of parental phage DNA. Addition of chloramphenicol 4.5 min after phage was added permitted the onset of phage-directed DNA synthesis but prevented breakdown of phage DNA. Mutants of T7 (ss(-) mutants) have been isolated which show normal growth in strain D(2) 371-48. Upon mixed infection of this strain with T7 wild type and an ss(-) mutant, infection was abortive; no complementation occurred. The DNA of the ss(-) mutants was degraded in mixed infection like that of the wild type. Revertant mutants which have lost their ability to grow on D(2) 371-48 were isolated from ss(-) mutants; they are, in essence, phenotypically like T7 wild type. Independently isolated revertants of ss(-) mutants did not produce ss(-) recombinants when they were crossed among themselves. When independently isolated ss(-) mutants were crossed with each other, wild-type recombinants were found; ss(-) mutants could then be mapped in a cluster compatible with the length of one cistron. We concluded that T7 codes for an active, chloramphenicol-sensitive function [ss(+) function (for suicide in Shigella)] which leads to the breakdown of phage DNA in the Shigella host.
mesh_terms: D001433:Bacteriolysis; D002701:Chloramphenicol / Q000494:pharmacology; D003090:Coliphages / Q000502:physiology*; D003470:Culture Media; D004269:DNA, Bacterial / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism; D004926:Escherichia coli; D005827:Genetics, Microbial; D009154:Mutation; D012764:Shigella sonnei / Q000502:physiology*; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D014466:Ultraviolet Rays
chemical_list: D003470:Culture Media; D004269:DNA, Bacterial; D004279:DNA, Viral; D014316:Tritium; D002701:Chloramphenicol; D013936:Thymidine