Phage Variants Research Articles

λ alt SF: A phage variant that acquired the ability to substitute specific sets of genes at high frequency

λ <i>alt</i> SF: A phage variant that acquired the ability to substitute specific sets of genes at high frequency

Lambda altSF: a phage variant that acquired the ability to substitute specific sets of genes at high frequency.

We report the isolation of lambda altSF, a variant of Escherichia coli phage lambda that substitutes sets of genes at high frequency. Two forms of the variant phage have been studied: lambda altSF lambda, which exhibits the immunity (repressor recognition) of phage lambda, and lambda altSF22, which exhibits the immunity of Salmonella phage P22. Lysates made from single plaques of lambda altSF lambda contain 10-30% phage of the P22 form. Similarly, lysates from single plaques of lambda altSF22 contain as much as 1% phage of the lambda form. Heteroduplex analyses reveal the following features of the lambda altSF chromosomes: (i) each form has the immunity genes appropriate to its immune phenotype, (ii) the substituted segments include genes involved in regulation and replication, and (iii) the alt phages have unusual additions and substitutions of DNA not normally found associated with either immunity region. In the case of lambda altSF lambda, there is a small insertion in the region of the cI gene. Because revertants that lose this inserted DNA concomitantly lose the ability to substitute, we conclude that the insertion plays a role in the substitution process. In the case of change from lambda altSF lambda to lambda altSF22, the substituting P22 genes are derived from the E. coli host. We have identified a set of Salmonella phage P22 genes in a standard nonlysogenic strain of E. coli K-12 that is apparently carried in a silent form. The reason for this lack of expression is not obvious, because this P22 material includes structural genes and associated promoters and is potentially active. When this set of genes substitutes for the analogous set of genetic material on the genome of lambda altSF lambda, the P22 genes are expressed in a normal manner.

Integrative recombination of bacteriophage lambda DNA in vitro.

An in vitro system for the production of integrative recombinant DNA of bacteriophage lambda is described. The in vitro recombination mimics the in vivo integration of viral DNA into host DNA in its requirement for int gene product, for the presence of a thermolabile component, and for the limitation of the recombination to a pair of specialized sites (attachment sites) on the DNA. The enzymes are extracted from Escherichia coli containing phage lambda gene products. The substrate is the DNA from lambda-attB-attP, a phage variant that contains two attachment sites on the same chromosome. The product is a recombinant phage chromosome that has lost the DNA between the attachment sites. The parental and recombinant DNA are distinguished following transfection to mature phage in spheroplasts. The reaction requires ATP, Mg++, spermidine, and a monovalent cation. Recombination occurs preferentially between attachment sites on the same molecule. The enzymatic activity is completely inhibited by extracts containing xis gene product.

Lysogenization and curing by int-constitutive mutants of phage λ

Abstract Stocks of phage variants carrying mutations ( o L c and int-c ) that allow transcription of the int gene of a repressed λ prophage have been derived from a lysogen in which λ is inserted into the trp operon so that part of that operon responds to phage promoters. Studies of these phages and lysogens derived therefrom show that o L c phages express genes N , red-γ, xis , and int under repression, whereas int-c phages efficiently express int alone. The int-c mutation has a dual effect on the xis gene. Very little functional xis product is formed by derepressed int-c phages; but repressed int-c phages mediate xis -dependent excision at a rate that is small yet higher than that observed with wild-type λ. This minute excisionase activity under repression is observed only when the int-c mutation is cis to a functional xis gene; which suggests that perhaps the int-c mutation causes production of an incomplete, partially active xis product.

Induction of an endonuclease by some substitution and deletion variants of phage λ

Induction of an endonuclease by some substitution and deletion variants of phage λ

The multiplication of staphylococcal phages in nonpermissive hosts.

Determining the phage susceptibility of staphylococci is complicated by the appearance of “inhibition,” in which concentrated phage suspensions produce confluent lysis, but no dilution of the phage suspension produces distinct plaques. Variants of typing phage 81 were found to inhibit cultures A17 and A19. The multiplication of phage in these nonpermissive hosts was studied by using more sensitive indicator strains for phage assays in one-step growth experiments. The phage produced was neither host-modified nor mutant. Since there have been reports of endemic hospital infections due to untypable strains inhibited by group III phages, two such strains, CL-4 and CL-63, were studied for production of typing phages 47 and 53. It was found that inhibition may be associated with either a normal burst of phage from a small fraction of infectious bacterial centers or with the release of a reduced burst from a higher proportion of infectious centers. The multiplication of phage in some cells of these nonpermissive hosts appeared to depend upon the physiological state of the culture as well as the genetic potential of the phage.

Influence of resistance-factors on the phage types of Salmonella panama.

The resistance to antibiotics which has been increasingly observed in naturally occurringSalmonella panama, is due to an R-factor. A relationship was found between phage pattern and the presence of this R-factor. All strains belonging to phage types A, C and E are sensitive to all antibiotics and are indicated in phage-typing by wild-type phage 47 or host-range mutants of phage 47. All strains belonging to phage types B, D and F possess an R-factor and are indicated by host-modified variants of phage 47. Phage type G, indicated by a host-range mutant, and group Z contain strains with, as well as without an R-factor. Spontaneous drug-sensitive segregants of type B, D and F strains have the phage pattern A, C and E respectively. Conversely, the phage pattern of A, C and E type strains change into B, D and F respectively after infection with the R-factor ofS. panama. The theory can be advanced that type B type A+R-factor, D — C+R-factor and F = E+R-factor. This change in phage type can be considered to be due to the fact that the R-factor exerts restriction and modification of the phage which indicates theS. panama strain without the R-factor. Many of the antibiotic-resistantEscherichia coli strains found in nature possess an R-factor which can be transferred toS. panama in vitro. Relatively few of these R-factors were found to possess also the restriction marker. Thus up to the present the number ofE. coli strains possessing an R-factor which is able to create a dependable combination of phage type and drug resistance inS. panama is relatively small.

Spontaneous mutation and recombination among brucellaphages.

Merz, George S. (University of Wisconsin, Madison), and Joe B. Wilson. Spontaneous mutation and recombination among brucellaphages. J. Bacteriol. 91:2356-2361. 1966.-Two plaque morphology variants, as seen on Brucella abortus 544A, termed c (for clear plaque) and lc (for late-clearing plaque) were isolated from stocks of wild-type brucellaphage and from colonies of B. abortus 544A which had undergone an alteration in colonial morphology associated with the establishment of the phage carrier state. Single-burst experiments showed that the phage variants arise by spontaneous mutation of the wild-type phage during its replication on B. abortus strain R19. Two-factor crosses of independently occurring c mutant phages showed the presence of wild-type recombinants among the progeny. Control experiments showed that there are no strong selective forces against either wild-type or c mutant phage inherent in the cross-procedure. Other control experiments ruled out the possibility that wild-type phage in the cross-progeny resulted from either back mutation of the c mutants or the presence of wild-type phage among the input c mutants.

Some phages released from P22-infected Salmonella

Abstract P221 phage are variants of P22 phage with altered morphology, host range, serological properties, etc. P221 phage occur in P22 phage lysates grown on Salmonella typhimurium strain LT-2 (Yamamoto and Anderson, 1961) . Both the substrain of the phage and the substrain of the host influence the frequency of variant phage found in the lysates. Bacteria infected either with a mutant of P22 defective in antigen conversion (P22 a 1) or with a phage similar to P22 in all other properties tested (P22-11) give rise to variant phage with greater than 1000-fold increased frequencies. A variety of genetically heterogeneous phages is released from S. typhimurium infected with P22 phage and from double lysogens carrying P22 and P221 prophages. A new nomenclature for designations of strains of these phages is introduced, and the properties of prototype phage strains are summarized (Table 10). Among the variant phages are some new types not previously described. One variant, termed P22-3, was obtained as a single-plaque isolate of phage P221. P22-3 differs from a prototype P221 stock (designated P22-1) in its morphological and immunity properties. P22-3 differs from P22 in all properties studied: morphology, host range, mean buoyant density, latent period, serological specificity, and immunity. Another new variant phage, termed P22-12, was isolated from a double lysogen carrying P22 and P221. P22-12 differs from each of these phages in host range, serological specificity, and immunity.

The irregular plaques on &lt;i&gt;E. coli&lt;/i&gt; B, formed by a T3 phage variant

以上を要約すると次のようになる。T3ファージ抵抗性菌の集落の中に見出される扇形集落を斜面培地で何代か継代すると, はじめはB株上で円形の溶菌斑を形成する T3hファージが, 同じB株上に不整形の溶菌斑を形成するファージ集団に置きかえられているのを見出した。これを T3hs と名付けたが, このファージの Bs/3 株で増殖したもの [T3hs (Bs/3)] は, B株上に不整形のBs/3株上に円形の溶菌斑を形成し, B株で増殖したもの [T3hs (B)] は, B株上にも Bs/3 株上にも円形の溶菌斑を形成した。

The isolation of a staphylococcal phage variant susceptible to an unusual host control.

A series of phage P(1) variants was isolated from plaques developing on S. aureus WF 145. One in particular, phage 14, was studied in detail because its host range appeared to be dependent on the previous host of production; i.e., it was subject to a host control. When this phage was produced on host K(1) its lysate assayed equally well on both 145 and K(1) cells. When produced on host 145, however, it assayed manyfold higher on 145 than on host K(1). All its particles adsorbed on K(1) cells, but only a small percentage were able to produce plaques. No differences could be found in adsorption rates, latent periods, or burst sizes of the phage on the two hosts. No extracellular inactivating substances could be detected which could account for such changes, nor could the results be explained readily on a mutational basis, since distinct phage strains could not be isolated. The change in virus properties was found to occur in the first burst of singly infected host 145 cells, regardless of the previous host or its prior lytic abilities. Heat inactivation destroyed activity for K(1) cells more rapidly than for 145 cells. This was found to be a property of both the stock phage P(1) and phage 14. Phage 14 could be heated until there remained particles which could multiply only on strain 145. When the plaques of such survivors were examined they were found to contain phage which could multiply on both hosts in a ratio characteristic of the original unheated preparation. The data suggest that the observed changes were caused by a host control over the formation of a phage material(s) necessary for successful infection of host K(1). Such a substance theoretically could be related to the labile material destroyed by heat and required for plaque formation on host K(1).

A preliminary study of the bacteriophages ofPseudomonas aeruginosa

Thirty strains ofPseudomonas aeruginosa, isolated from routine clinical material, were investigated, with particular reference to the metallic lytic effect and the bacteriophages they carry. From the filtrates of these strains, twenty-five bacteriophages or phage variants were isolated, and the effect of these on the various bacterial strains and some of their variants were investigated.It has not been possible to elucidate the nature of the agent responsible for the metallic lytic effect. The true phages isolated, however, present many features of interest which warrant their more detailed study.Part of this work was carried out in the Nkana Kitwe and C.S.I.R. virus research unit at the U.C.T. Pathology Department.