Inhibitory effect of fatty acids on the entry of the lipid-containing bacteriophage PR4 into Escherichia coli

Various unsaturated fatty acids (notably palmitoleic acid and oleic acid) interfered with plaque production by the lipid-containing bacteriophage PR4 on lawns of Escherichia coli. Addition of fatty acid to give 50 mug/ml ( approximately 0.2 mM) at the time of infection prevented phage replication. If, however, the fatty acid was added after infection, normal amounts of phage were produced. If the fatty acid was added (to 50 mug/ml) to the host cell culture a long enough time before infection such that the fatty acid concentration in the growth medium at the time of infection was reduced to less, similar5 mug/ml (due to fatty acid incorporation by the host cells), normal phage replication occurred also. Neither palmitoleic acid nor oleic acid prevented PR4 attachment to E. coli. Several types of experiments indicated that it is the entry process of the virus that is inhibited by these fatty acids. Specifically, if the fatty acid was added at the time of infection, the host cells were not killed by the virus and no detectable amounts of viral protein were synthesized. In addition, experiments using purified radioisotope-labeled virions showed directly that entry is inhibited. Mutants of PR4 that did replicate in the presence of oleic acid arose spontaneously at a frequency of 10(-6). Three of these mutants that have been further characterized have protein and phospholipid compositions indistinguishable from those of wild-type PR4.

Isolation of a Bacillus subtilis 168 derivative sensitive to defective bacteriophage PBSX

A derivative of Bacillus subtilis strain 168 sensitive to defective bacteriophages PBSX and PBSZ has been isolated. This particular strain, RUB824, carries the genetic information for defective bacteriophage PBSX.

Phage-induced changes in Vibrio cholerae: serotype and biotype conversions

Phage infection of Vibrio cholerae resulted in antigenic changes. A strain of biotype cholerae serotype Ogawa was converted into serotype Hikojima and gained the ability to synthesize antigenic factor C. Some phage-converted strains remained stable after subculture and were immune to superinfection with the same phage. The stable converted strains were lysogenic and released phage having a host range similar to the phage of the donor strain. Reinfection of unstable converted strains which had "lost" antigen C yielded types able to again synthesize this antigen. The polymyxin resistance character was expressed in the biotype cholerae strain after infection with some phage preparations. These polymyxin-resistant strains possessed three main characteristics of El Tor vibrios. The phage-induced changes described provide V. cholerae with the potential for innumerable genetic combinations.

Characterization of the virulent actinophage S2

The virulent actinophage S2 isolated from soil infects Streptomyces hygroscopicus 6599, S. lividans 66, and S. levoris 1331. Morphology of S2 was studied by electron microscopy. Influence of growth medium and temperature on multiplication of S2 has been studied qualitatively. S2 is more sensitive to UV irradiation on strain 66 than on 1331. In contrast to UV, hydroxylamine mutagenesis delivered 9 stable ts mutants which belong to 3 complementation groups. Most of the ts mutations isolated on 1331 were found to be host dependent, 8 of 9 mutants were found to be able to grow at 40 degrees C on strain 66 but none of them on 1331. Moreover 2 of the mutants were found to be much more heat sensitive in 6599 than in 1331, as indicated by the changes in half-life temperatures. The latent period of S2+ depends on temperature and germination state of the spores. Under optimal conditions we found 140 min. Ts2 and ts7 have been classified as a late and ts17 as an early mutant.

Transfection in pneumococcus: single-strand intermediates in the formation of infective centers

Transfection has been found and characterized in pneumococcus. For replicating omega3 phage DNA extracted from infected cells, transfection was relatively efficient and rose linearly with DNA concentration and quadratically with time, according to T(T - 3.5) min(2). For mature DNA extracted from phage particles, transfection was hardly detectable below 1 mug/ml but increased about as the cube of the DNA concentration up to 100 mug/ml, and was still rising at concentrations over 200 mug/ml. The kinetics suggest a dependence on a mixed cubic function of the time of exposure of cells to mature DNA. Cell and phage DNAs competed with each other for transformation and transfection. Transfection was reduced much more strongly than transformation in cells that were deficient in the membrane-bound endonuclease required for conversion of donor duplex DNA to intracellular single strands; these data agree with the kinetic data in implying that independent entry of segments of two strands is necessary for transfection by replicating omega3 phage DNA and entry of at least three strands is necessary for transfection by mature DNA. To reconcile differing DNA concentration dependences of transfection and transformation with a common entry path, it was necessary to reexamine data on transformation and to recognize that this process continued to rise slowly through the concentration region usually described as "plateau." These results and the transfection data reflect multiple binding and nicking events that occurred on the cell surface before entry. Our conclusion is that transfection in pneumococcus occurs by association inside the cell of segments of single strands of phage DNA that have entered independently, creating gapped structures that need repair synthesis to create infective centers. Physical recombination is therefore automatically a prerequisite to transfection.

Isolation and some properties of nontoxigenic derivatives of a strain of Clostridium tetani

Nontoxigenic derivatives of a toxigenic strain of Clostridium tetani were isolated gy treatment with acridine orange, N-methyl-N'-nitro-soguanidine, rifampicin or ultraviolet light. The frequency of appearance fo non-toxigenic derivatives on these treatments was 0.8 to 3.2 per cent. The nontoxigenic derivatives peoduced all the same extracellular antigenic and protein components as the toxigenic parent strain, except the toxin and materials cross-reacting with the toxin. The nontoxigenic strains, like the toxigenic parent strain, were lyzed by trratment with mitomycin C. Bacteriophage was detected in the lysates of all the nontoxigenic derivatives produced with mitomycin C, and this bacteriophage was morphologically indistinguishable from that obtained from the toxigenic parent strain. The genetic factor controlling tetanus toxin production is discussed.

On the dose response in B. subtilis transfection: involvement of aggregates in phi 29 transfection

Transfection with phi 29 DNA is predominantly caused by multimolecular, protease-sensitive aggregates of DNA. A minority of transfecting DNA molecules having properties of unit-length phi 29 genome molecules show a quadratic dose response in transfection.

Transduction, by phases F116 and G101, of gentamicin-tobramycin resistance, and of "autoplaque formation" property in Pseudomonas aeruginosa

Pseudomonas aerugionsa phages F 116 and G 101, propagated on ML 4262 strain into which gentamicin-tobramycin resistance determinants have been increased by means of conjugation, from wild-type strains Vy 28, 29 and 34, were capable to transduce R determinants to PAO 1670 strain. Transfer ability was co-transduced as well, with exception of transductants selected with streptomycin. "Autoplaque formation" ability, occurring in original wild-type strain Vy 28, could be co-tranduced with all tobramycin-resistant determinants by F116 but not G 101 phage.

Deletion mutants of temperate Bacillus subtilis bacteriophage phi105

Six deletion mutants of temperate Bacillus subtilis phage phi105 have been isolated on the basis of their increased resistance to chelating agents. The size and position of the deletions was determined by electronmicroscopy of DNA heteroduplexes. All deletions are located in a region about 55-70% from one end of the DNA molecule, in the right half of the known genetic map of the phage. The segment 55-65% does not contain any genes essential for lytic growth or lysogenization. A gene(s) for immunity is located in a segment 65-70% from the left end. By electronmicroscopy by partially denatured phi105 DNA two A-T rich regions have been localized in the right half of the molecule. One of these regions falls within the non-essential 55-65% DNA segment.

Order of the two major head protein genes of bacteriophage phi 29 of Bacillus subtilis

Bacteriophage phi 29 mutation sus8(22) has been mapped by two-factor crosses between markers sus8(769) and ts8(93). Whe sus8(22) infects Bacillus subtilis su- proteins, HP1 (major head protein) and HP3 (fiber protein) are not synthesized; instead, a fragment with a molecular weight of 25,000 is produced. The tryptic peptides of the fragments overlap with corresponding peptides in protein HP1, but not with the peptides of protein HP3, showing that cistron 8 codes for the major head protein HP1.

Isolation from corynebacterium diphtheriae C7(beta) of bacterial mutants that produce toxin in medium with excess iron

Five mutants that produce toxin in medium with excess iron were isolated from strain C7(beta). The iron content of bacteria grown on this medium was considerably higher than that of C7(beta) cells grown in medium containing the minimum amount of iron needed to inhibit toxin production. When the nonlysogenic, nontoxinogenic strain C7(-) was lysogenized with phages from each of the mutants, toxin production by all of the resulting lysogens, like that by parent strain C7(beta), ceased upon iron addition. When the mutants were superinfected with beta45 phage, both toxin and CRM45 were produced in medium with excess iron. One of the mutant strains lost its prophage as a result of treatment with ultraviolet light. When the cured strain was lysogenized with phage carrying a mutation in the tox structural gene, the lysogen produced the mutant protein at the maximum rate in medium with excess iron. These findings show that the mutant strains are not phage mutants, but are bacterial host mutants, and that a host factor(s) is involved in the inhibition of toxin production by iron.

Morphogenesis of bacteriophage phi 29 of Bacillus subtilis: mapping and functional analysis of the head fiber gene

A set of mutants of Bacillus subtilis bacteriophage phi29 unable to synthesize the head fiber protein has been identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. Infectious phage are produced during restrictive infection. We have focused on mutant sus 8.5(900) because the mutation is suppressible by both the su(+3) and su(+44) hosts, and it can be mapped by three- and four-factor crosses. After restrictive infection with mutant sus 8.5(900), a fragment about 70% of the size of the normal fiber is produced as well as particles that are fast-sedimenting in sucrose gradients relative to phi29(+). These particles have the buoyant density of particles with the fibers removed and have the absolute plating efficiency of phi29(+). Fiber protein is absent from prohead as well as virion. A second set of mutants produces fiber protein with a slightly altered electrophoretic mobility. This type of fiber protein is either present or absent on both prohead and virion. A third class of mutants, typified by 914, produces a "normal" fiber, but a major head protein of altered electrophoretic mobility. After infection by this mutant, the fiber is absent from both prohead and virion, and the biological and physical properties of the 914(-) particle are similar to those of particles produced after infection of the su(-) host by sus8.5(900). These observations suggest that the head fiber is not an essential component of the prohead or virion and that the assembly process is efficient in the absence of fiber protein. Three- and four-factor genetic crosses have established the order sus8(769)-8(914)-sus8.5(900)-sus9(756) and indicate that cistrons 8 and 8.5 code for the major head protein and head fiber protein, respectively.

Nucleotide sequences near the origin of replication of bacteriophage f1

The nucleotide sequence of a region related to the initiation of the reaction in which single-stranded DNA gives rise to the replicative form (complementary strand synthesis) in bacteriophage f1 has been determined. The sequence can be drawn in an extensively base-paired structure, i.e., a single hairpin-helix 55 bases long.

[Effect of the protein product of phage f1, gene 5, on heat denaturation of synthetic polynucleotides]

The influence of phage f1 gene 5 protein on melting of the synthetic polynucleotides has been investigated, using UV-spectroscopy. In our experiments we have varied the proteins concentration. It has been shown, that the protein lowers the melting temperature of the studied polynucleotides (d/A--Tn dAndTn, rAndTn, rAn.r n, dAn.rn). The melting temperatures and the shapes of melting curves of various polynucleotides differ when the same protein concentrations are used. We have shown that the protein binds to the double-stranded polynucleotides, containing ribo-ribo-, deoxyribo-ribo-chains. The difference in melting temperatures and shapes of melting curves was explained using the data about the differences in the secondary structure of these polynucleotides. Only for d/A-Tn renaturation was observed after sample cooling. It may reflect the single-stranded hairpin structure of this polynucleotide.

Development of bacteriophage phi29 in sporulating and non-sporulating cells of bacillus subtilis 168

Infection by bacteriophage phi29 of Bacillus subtilis 168 and of its asporogenous mutant spoOA-3NA has been studied in exponential and stationary phases. As first observed with phage phie infections, the burst-size decreases during the stationary phase much more rapidly in wild type than in mutant cells. In addition, the two strains are shown to differ even during growth in their response to phage phi29 infection. During a short period in the exponential phase, no phage production occurs when infected bacteria (whether spo+ or spo-) are incubated in their growth medium, but phage is produced when incubation takes place after transfer to fresh medium. From these and other unexpected findings it is concluded that any causal relation between sporulation and phage development must be considered with caution. Phage infection of spo+ cells at the end of the growth period does not affect the time required for mature spore formation.

Influence on motility of Escherichia coli and Salmonella typhimurium by a naturally occurring conjugative plasmid

In a collection of 45 R-plasmids, one was found to be associated with loss of motility of its Escherichia coli K-12 and Salmonella typhimurium host bacteria when tested in conventional motility agar. Genetic experiments, as well as analyses of deoxyribonucleic acid, showed that inhibition of motility was caused by a conjugative plasmid that was separate from the R-plasmid. This second plasmid, named pUM5, was fi- and mediated the same type of sex pilus (F-like) as the accompanying R-plasmid but lacked resistance determinants. Preliminary studies indicated that bacterial cells carrying the motility inhibition plasmid pUM5 were still equipped with flagella. The mechanism by which flagellar action is disturbed by the plasmid is presently not known.

Characterization of Pseudomonas aeruginosa derepressed R-plasmids

A genetic study of conjugal transmissibility of two R-plasmids was undertaken in Pseudomonas aeruginosa. Conjugally derepressed mutants of the R-plasmids were isolated, and examination of 11 independent mutants revealed that 10 were recessive to the wild-type transfer repressor, whereas 1 mutant was cis dominant. Cross-repression was observed between the two R-plasmids, suggesting that they have functionally equivalent systems for regulating the expression of tra loci. The derepressed R-plasmid mutants exhibited several characteristics, in addition to derepressed transfer, that were not expressed by the parental plasmids. These included sensitivity to certain donor-specific phages, inhibition of multiplication of a transducing phage, and, in the one case examined, a high degree of entry exclusion. The coexpression of these different functions suggests that their respective genetic loci are controlled by the same regulatory system as that of tra, or else that they are part of the tra complex.

Effect of site-specific endonuclease digestion on the thyP3 gene of bacteriophage phi 3T and the thyP11 gene of bacteriophage rho11

phi 3T and rho11 are closely related bacteriophages of Bacillus subtilis which can "convent" thymine auxotrophs to thymine prototrophs upon infection or transfection. The effect of endonuclease digestion on the ability of both bacteriophage and prophage DNA from phi eT and rho11 to transform for thymine prototrophy was determined. All of the endonucleases tested: BamHI, Bg/II, BsuRI, EcoRI, HindII+ III, and HpaII reduced the efficiency of thyP transformation to an equal extent in prophage and bacteriophage DNA. Only HpaII completely abolished thyP transformation. The reduction in transformation with BamHI, Bg/II, BsuRI, EcoRI, and HpaII fragments is size related. The thyP transforming fragments generated by these endonucleases are potentially clonable.

Transformation of Bacillus subtilis and Escherichia coli by a hybrid plasmid pCD1

The gene thyP3 from Bacillus subtilis bacteriophage phi 3T was cloned in the plasmid pMB9. The resulting chimeric plasmid, pCD1, is effective in transforming both Escherichia coli and Bacillus subtilis to thymine prototrophy. The activity of the thyP3 gene product, thymidylate synthetase, was assayed and found to be 9 times greater in a transformed strain of Escherichia coli than in a phi 3T lysogen of Bacillus subtilis. The physical location of restriction sites has been determined for two related plasmids pCD1 and pCD2. Hybridization studies clearly indicate that the plasmid gene responsible for Thy+ transformation is the gene from the bacteriophage phi 3T. The lack of restriction in this transformation process is consistent with our previous studies using bacterial DNA in heterospecific exchanges indicating that the nucleotide sequence surrounding the gene is the dominant factor in determining interspecific transformation.

Generation in vitro of deletions in the broad host range plasmid RK2 using phage Mu insertions and a restriction endonuclease

Several non-lethal deletions of the broad host range plasmid RK2 (molecular weight of 37.6 . 10(6) have been produced in vitro. The method employed relied on the single HindIII restriction nuclease site in RK2 and the ability of phage Mu to insert and thereby add new HindIII restriction sites at various positions in the plasmid. The deleted plasmids have in each case lost kanamycin (Km) resistance, and in two cases are defective in self-transmissibility. The method used to reduce the size of the RK2 plasmid also results in the cloning of each of the two ends of the Mu phage DNA on the plasmid derivatives.

In vitro site-directed mutagenesis: generation and properties of an infectious extracistronic mutant of bacteriophage Qbeta

An infectious extracistronic mutant of phage Qbeta has been prepared by site-directed mutagenesis. Qbeta RNA minus strands containing the mutagenic base analog N4-hydroxy-CMP instead of UMP at position 39 from the 5' end were synthesized in vitro and used as template for Qbeta replicase to synthesize one generation of plus strands. E. coli spheroplasts were infected with the newly synthesized plus strands and phage recovered from single plaques. RNA sequence analysis revealed that four out of the eighteen phage clones analyzed contained RNA with an A leads to G transition at position 40 from the 3' end (which corresponds to position 39 of the minus strand). Thus, the viability of phage Qbeta does not depend on a unique nucleotide sequence in the 3'-extracistronic RNA segment. Upon in vivo propagation of mutant 40, spontaneous true revertants arose with high frequency and overgrew the parental clone within about 10 passages, indicating a selective disadvantage of the extracistronic mutant. Replication of mixtures of wild type and mutant RNA in vitro resulted in a decrease of the proportion of mutated RNA in the progeny plus strands. The fact that Qbeta RNA containing an A leads to G transition in nucleotide--40 of Qbeta RNA is less efficiently replicated in vitro may explain the selective disadvantage of the mutant phage in vivo. The preparation of an infectious mutated RNA by site-directed mutagenesis shows that the method is suitable to produce specific nucleotide exchanges without impairing the biological competence of the RNA.

Inactivation of bacteriophage, DNA, and ribonuclease by thermal hydrogen atoms

T1 phage, BU-T1 phage, infectious DNA extracted from phage phiX 174, and chromatographically purified ribonuclease were exposed to thermal hydrogen atoms, and the loss of plaque-forming ability, infectivity, or enzymatic activity was determined after various exposure times. Atomic hydrogen was generated by two different methods: (1) by a high-frequency discharge in hydrogen gas and (2) by irradiating a foil of polyethyleneter-ephthalate with 2-MeV protons. With increasing exposure time the surviving fraction of all objects tested approaches a constant level. After subtracting this constant "indestructible" fraction in either system, all objects were inactivated according to exponential curves. Furthermore, no BU sensitization was found to occur in BU-T1 phage exposed to atomic hydrogen, whereas gamma irradiation of samples from the same batches revealed a BU effect of a factor of 2.2. These experiments demonstrate hydrogen atoms to be efficient in causing biological damage. Consequently the terminology of "direct" and "indirect" radiation effect may have to be redefined.

Bacteriophage Genes and Bacterial Functions: The viruses that attack bacteria control properties of their host cells by action of specific genes

This brief survey of bacteriophage infection has provided support for an obvious but important generalization: that the study of virus infection at the cellular level is a branch of cellular genetics. The interactions between viral and cellular functions show that infection with a virus is not just a disrupting intrusion; it is an addition to the cellular endowment of genetic specificity. The outcome of this addition depends on the nature of the instructions carried by the viral genome, on the ability of the cellular machinery to carry out these instructions, and on the availability of control mechanisms to regulate the functions of the added element.