Isolation of a clear plaque-forming mutant of Escherichia coli for infectivity assay of filamentous phage fd

A fd clear plaque-forming mutant of Escherichia coli K37 has been isolated among progeny treated with N-methyl-N′-nitroso-N-nitrosoguanidine. Although the growth of this mutant (CPF30) is strongly inhibited by fd infection, phage production is observed at a fairly good rate. This mutant is useful for fd plaque assays.     

An Escherichia coli mutant which inhibits the injection of phage lambda DNA

A new mutant of Escherichia coli K12, called pel^?, inhibits the growth of phages λ, 434, and 82 but not of φ80. This inhibition is overcome by λhp mutants, some of which are temperature sensitive for growth in pel⁺ and pel^? bacteria.Phage λ adsorbs normally to the pel^? host, but only 2–10% of the infected cells produce phage with a normal burst size or become lysogenic. The remainder of the cells survive the infection. The growth defect of λ cannot be complemented in trans upon simultaneous infection with λhp. When pel^? strains lysogenic for λ are induced, 100% of the induced cells yield phage, and the burst size is normal in contrast to the small probability of phage growth after infection.After adsorption of λ to pel^? cells, active phage do not elute spontaneously from the complex. Neither are adsorbed phage released in an inactivated form.Infection of pel^? (P1) with ³²P-labeled unmodified λ does not lead to degradation of the phage DNA by P1-specific restriction, whereas the DNA of λhp is degraded. Electron micrographs of λ infected cells show phage particles with empty heads attached to the surface of pel⁺ cells, while the particles attached to pel^? cells appear to have full heads.We conclude that the pel^? mutant allows adsorption of λ but that it inhibits the subsequent injection of the phage DNA.     

A transactivation mutant of satellite phage P4.

A mutant of satellite phage P4, δ6, was isolated as a thermosensitive mutant on the basis of its plaque-forming ability on Escherichia coli C(P2⁺). Complementation tests show that this mutant defines a new P4 gene, called δ. Unlike P4 wild type, P4 δ6 depends on the gene A function of its P2 helper at all temperatures, whether the helper is supplied as a prophage or as a coinfecting phage. The P2 gene A product is required both for P2 DNA replication and for P2 late gene expression (Lindahl, G. (1970) Virology42, 522–533). P2 DNA replication is critical for growth of P4 δ6, since host mutations which block P2 DNA replication prevent production of P4 δ6 progeny, whereas they allow P4⁺ to multiply. The δ6 mutation makes P4 unable to activate P2 late mRNA synthesis from nonreplicating P2 phage. Thus, P4 δ6 is defective in transactivation.     

The sim gene of Escherichia coli phage P1: nucleotide sequence and purification of the processed protein

The sim gene of bacteriophage P1 causes exclusion of a superinfecting P1 phage. We determined the nucleotide sequence of a 1.9-kb DNA fragment that, in plasmids, causes Sim phenotype. There are two open reading frames within this region for proteins of 82 and 259 amino acids. A 1.3-kb fragment containing the larger open reading frame was inserted into an expression vector. Induced cells carrying the hybrid plasmid, termed pBD5, were not infected by phage P1 and produced a 24-kDa protein and, to a smaller extent, a 25-kDa protein. The 24-kDa protein was purified. Comparison of its amino-terminal amino acid sequence with the nucleotide sequence indicated that it is processed from a precursor protein by removal of a hydrophobic leader peptide of 20 amino acids. In vivo processing depends on secA gene function and is necessary for Sim interference with P1 infection. The data are discussed with respect to the function of the sim gene in superinfection exclusion.     

Overproduction of a viral protein during infection of a lyc mutant of Escherichia coli with phage lambdamm434

The bacterial lyc7 mutation probably affects the same gene as the hf1 mutation described by Belfort and Wulff and promotes increased lysogenisation by lambdoid phages. The synthesis of lambdoid phage-specific proteins has been examined after infection of ultraviolet light-irradiated lyc+ and lyc7 Escherichia coli strains, and a new protein with a molecular weight of 14,000 was observed to appear during infection of the mutant but not of the wild type. This protein may be the product of the phage cII gene.     

Mutations in bacteriophage lambda that alter phage dependence on the htpR gene product of Escherichia coli

Six mutants of lambda having reduced dependence on the htpR function of Escherichia coli were isolated from lambda cIts857. Burst sizes in htpRts cells at 40.5 degrees were in the range of 10 to 20 particles per cell. Mapping and complementation analysis of one of the mutants suggested that the mutation in this isolate is in gene J. Additional evidence that the mutations in most of the isolates are in J was provided by the finding that all but one of the mutants differ from the parental phage in properties pertaining to extended host range.     

Formation of phage T1 concatemers by the RecE recombination pathway of Escherichia coli

Infections of nonpermissive ( sup0 ) Escherichia coli by T1 phage with amber mutations in either gene 3.5 or gene 4 exhibit a variety of defective phenotypes, including premature arrest of T1 DNA synthesis, failure to make concatemeric DNA, formation of an abnormal DNA replication intermediate, failure to package phage DNA, and reduced genetic recombination. The lethal effect of gene 3.5 or 4 mutations is suppressed when the sup0 bacteria express the RecE recombination pathway. This RecE suppression occurs by partial restoration of the capacity to make concatemeric molecules and partial reversal of the DNA arrest defect which, in turn, leads to the formation of viable progeny. Infection by T1+ or by mutants defective in any of the four DNA synthesis genes (genes 1, 2, 3.5, and 4) inhibited the ATP-dependent exonuclease present in uninfected cells (presumably the RecBC enzyme, exonuclease V). Extracts from T1+ infections also showed increased levels of an ATP-independent exonuclease activity which was absent from gene 4 mutant extracts. It is concluded that gene 4, together with gene 3.5, specifies an activity related to that of the RecE exonuclease VIII and essential for T1 concatemer formation and recombination.     

Enterotoxigenic Escherichia coli Strains that Express K88 and 987P Pilus Antigens

Two enterotoxigenic Escherichia coli strains from different sources expressed K88 and 987P pilus antigens.     

Shiga-like toxin converting phage of enterohemorrhagic Escherichia coli strain 933

Production of Shiga-like toxin (SLT) by enterohemorrhagic Escherichia coli (EHEC) is controlled by phage conversion, and specific phages carry either the SLT-I or SLT-II operon. EHEC strain 933 produces both SLT-I and SLT-II. Previous studies demonstrated that the vast majority of phages recovered from strain 993 have hexagonal heads with short tails and encode SLT-II. However, conflicting results were obtained concerning the properties of SLT-I converting phages from strain 933. The present study reexamined the recovery of phages from 933 by various methods and characterized the restriction fragments from strain 933 DNA that hybridized with radiolabeled DNA from the SLT-I converting phage 933J, which has an elongated head with a long tail, and the SLT-II converting phage 933W. In the present study, only SLT-II converting phages like 933W were recovered from strain 933. A set of restriction fragments that hybridized with DNA from phage 933J but not 933W was present both in wild type strain 933 and in the variant 933D, which produces only SLT-I and was shown here to be cured of phage 933W. The sizes of the restriction fragments in strain 933 that were homologous with phage 933J differed, however, from those of phage 933J. These data indicate that the phage we isolated and named 933J probably did not originate from strain 933 as we originally reported. The present evidence demonstrates that strain 933 contains both the SLT-II converting phage 933W and other sequences of DNA homologous with phage 933J that probably represent a defective SLT-I converting phage.