INFECTION OF PROTOPLASTS BY DISRUPTED T2 VIRUS

Safety evaluation of food enzymes produced by a safe strain lineage of Bacillussubtilis

The safety of microbially-derived food enzymes must be carefully assessed before market introduction. The production strain's safety is central to the assessment. In this paper, we have determined that DSM's Bacillus subtilis strain lineage can be considered safe for food enzyme production. The mutations introduced into this non-pathogenic and non-toxigenic microorganism do not lead to any safety concerns, as ensured by a thorough characterization of the strain lineage. The safety of both targeted and randomly introduced changes into the production strain's genome is confirmed by validating the absence of vector sequences and antibiotic resistance genes in all relevant production strains, and by demonstrating absence of cytotoxic peptide production. Furthermore, three food enzyme preparations produced by strains within this lineage did not show genotoxic potential. 90-day oral toxicity studies performed with the same enzyme preparations did not reveal toxicologically significant adverse effects. These results demonstrate absence of safety concerns from the introduced genetic modifications. Based on the establishment of this safe strain lineage, we postulate that future enzymes produced by current and new strains derived from the lineage can be safely developed without additional genotoxicity and systemic toxicity studies, allowing for a reduction of animal testing without compromising on product safety.

INACTIVATION OF A BACTERIOPHAGE BY CHEMICAL ANTIBACTERIAL AGENTS

An extinction method has been used to examine the inactivation of coliphage T6r by a number of chemical antibacterial agents. A marked difference in the effect of concentration on inactivation efficiency has been shown for different agents, chloramine-T and formaldehyde having concentration exponents of approximately 2 and 3 respectively; crystal violet, cetrimide and phenol having concentration exponents of approximately 11, 13 and 15 respectively. It is suggested that a low concentration exponent is associated with inactivation of the phage by an effect on the protein coat of the particle and a high concentration exponent with an effect on its internal structure.

INFECTION OF MYCOBACTERIUM SMEGMATIS WITH D29 PHAGE DNA

DNA extracted from D29 mycobacteriophage produced plaques when plated on Mycobacterium smegmatis 607. The host bacterium did not require alternation such as conversion to protoplasts; cells susceptible to infection with intact phage were susceptible to DNA. The bases found in calf thymus DNA constituted the bases of D29 DNA, adenine being paired with thymine and guanine with cytosine. The dissymmetry ratio (A + T/G + C) was 0.56, and the buoyant density in CsCl was 1.722 with a GC content of 63.77 per cent. The efficiency of plating of the DNA is very much lower than that of intact D29, and it penetrates the host at a slower rate. As does intact phage, D29 DNA requires calcium ions for productive infection of 607. D29 DNA is significantly inactivated by incubation with RNAase, but the inactivation probably results from a complexing with the DNA rather than from enzyme hydrolysis.

BACTERIOPHAGE DEOXYRIBONUCLEATE INFECTION OF COMPETENT BACILLUS SUBTILIS

Reilly, Bernard E. (Western Reserve University, Cleveland, Ohio), and John Spizizen. Bacteriophage deoxyribonucleate infection of competent Bacillus subtilis. J. Bacteriol. 89:782-790. 1964.-Phenol extracts of the Bacillus subtilis bacteriophages phi1, phi25, and phi29 contained infectious deoxyribonucleic acid. The infectivity was destroyed by catalytic amounts of deoxyribonuclease but not by specific phage antiserum, ribonuclease, or trypsin. An infectivity of >10(6) infectious centers formed per mug of deoxyribonucleic acid (DNA) added was obtained. The stability of the infectious centers permitted an examination of a single cycle of phage replication in cells unable to adsorb the mature virus. A typical cycle was observed, although the latent period was increased and the burst size slightly reduced after DNA infection. The development of competence for bacterial transformation was strongly correlated with susceptibility to viral DNA infection. Both appeared and disappeared at the same phase of growth in the cell population. More than 4% of the viable cells in the competent population were infected by viral DNA. The kinetics of the transition of phi29 DNA infection to deoxyribonuclease insensitivity, and the relationship of infectivity to DNA dilution, were similar to the results obtained for bacterial transformation of a single marker. The doseresponse curve of phi1 and phi25 DNA was characteristic of that obtained in multiple transformation of unlinked genetic markers. Because of the low efficiency of infection, about 10(-4) per phage equivalent of DNA added, it was not possible to prove that DNA alone was sufficient to initiate infection.

Bacterial characteristics determining the potential host range of bacteriophage T4

Many members of the Enterobacteriaceae, but not other gram-negative organisms, apparently carry a specific recognition site for the T4 tail tube on their cytoplasmic membranes.

Transfection mediated by Mycoplasmatales viral DNA

DNA isolated from Mycoplasmatales viruses MVL51 and MVGs51 was infectious when mixed with Acholeplasma laidlawii BN1-Na1(R) cells. Infectivity was destroyed by deoxyribonuclease but not by ribonuclease, Pronase, or specific antiserum to the virus. Host mycoplasma cells were only competent for transfection during late-log growth phase. The rates of the establishment of DNase insensitivity of viral DNA transfectants were similar to those of bacteriophage systems. The dose-response curve for transfection suggested that an average of six molecules of DNA must interact with a cell in order to produce one infectious center. Mycoplasmatales virus DNA exhibited a low efficiency of infection; one infectious center required 4 x 10(5) virus equivalents of DNA.

Transfection of Staphylococcus aureus with bacteriophage deoxyribonucleic acid

Staphylococcus aureus cells of strain 8325 (N) are competent for phage deoxyribonucleic acid (DNA) when harvested in the early exponential growth phase. Phenotypic expression of the competence requires divalent cations, and calcium ions are most effective. Treatment of phage DNA with deoxyribonuclease completely destroys infectivity and heat-denaturated DNA is not infectious. The highest frequency of transfection is around 10(4) plaque-forming units per mug of DNA.

Infection of actinomycin-permeable mutants of Escherichia coli with urea-disrupted bacteriophage

Intact cells of actinomycin-permeable mutants of Escherichia coli could be infected with urea-disrupted phage T4 (designated as T4pi). The parental strains and the revertants, which are impermeable to actinomycin, were not susceptible to T4pi unless they had been treated with agents which altered their permeability. The permeable mutants developed competence for pi infection during the growth cycle; cells in the early stationary phase produced 10- to 100-fold more plaques on plating with T4pi than did exponentially growing cells. Colistin (polymyxin E) was effective in converting noncompetent cells of either permeable or nonpermeable strains to the competent state. Treatment with lysozyme resulted in a considerable increase in susceptibility to T4pi of permeable mutants but not of nonpermeable cells. It appears that development of competence for pi infection is mainly due to alterations in the permeability barriers of the cell.

Multiplication of bacteriophage P22 in penicillin-induced spheroplasts of Salmonella typhimurium

The spheroplasts of Salmonella typhimurium (LT2) prepared by treatment with penicillin were capable of adsorbing phage P22 C(1). The normal multiplication of the phage took place, although the burst size was reduced to one-fourth of that in intact cells. Rate of incorporation of (14)C-thymidine into spheroplasts was increased severalfold on phage infection. Multiplication of C(+) also took place, but no lysogeny could be established in spheroplasts. Furthermore, spheroplasts prepared from cells lysogenized with wild-type phage, LT2 (C(+)), and a temperature-inducible C(2) mutant, LT2(tsC(2)), were not inducible. Unlike normal cells, both mitomycin C and actinomycin D interfered with the phage multiplication in spheroplasts. The spheroplast system offers great advantages in the study of the synthesis of nucleic acids and proteins in phage-infected LT2.

Transformation in quasi spheroplasts of Bacillus subtilis

RECENTLY DEVELOPED DIFFERENTIAL PLATING MEDIA PERMIT THE DISTINCTION OF FOUR CELL TYPES IN INCOMPLETELY PROTOPLASTED POPULATIONS: intact, osmotically insensitive bacilli; osmotically sensitive rods; spheres with adherent wall residues, called quasi spheroplasts; and protoplasts. Such population mixtures were washed free of lysozyme, and then transforming deoxyribonucleic acid (DNA) was added. Transformation was nil in the protoplasts, very low in the residual osmotically insensitive bacilli, and markedly enhanced in both osmotically sensitive rods and quasi spheroplasts. Transformation in the latter two population fractions was reduced, respectively, by about 60% and about 80% by deoxyribonuclease treatment. DNA adhering to the quasi spheroplasts transforms these cells only if they are permitted to resume wall synthesis; when the same cells are plated on a medium where they shed the residual wall and form L colonies, no transformant L colonies are recovered. It is inferred that far-reaching or complete protoplasting blocks all entry of transforming DNA into the cell interior. This may be owing to eversion of mesosomes. Evidence that intact mesosomes may be required for DNA entry is provided by the finding that the recovery of transformants in the intact cell system is sharply reduced on plating media containing 25% gelatin. On such media, cells expel their mesosomes and 75% of them do not re-form any. Our own data and a survey of published results suggest the generalization that partial depolymerization of the cell wall by lysozyme may enhance competence, whereas its complete removal abolishes it.

Transfection of lysostaphin-treated cells of Staphylococcus aureus

After treatment with 1 unit of lysostaphin per ml for 3 min, two strains of Staphylococcus aureus, 233 and PS 44A HJD, were transfected with phenol-extracted deoxyribonucleic acid (DNA) from the staphylococcal bacteriophages, 53 and 44A HJD, respectively. The number of transfected cells was low in both systems, approximately two in 10(7) enzyme-treated cells. There was a saturation effect at high concentrations of DNA; optimal results were obtained at concentrations between 10 to 25 mug/ml. Growth curves and fluctuation tests indicated that cells of strain 44A HJD infected with phage, then converted to protoplasts by a 10-min treatment with lysostaphin, produce only one phage particle and lose their ability to lyse spontaneously in hypertonic media.

Infection of competent Mycobacterium smegmatis with deoxyribonucleic acid extracted from bacteriophage B1

A relatively competent state of Mycobacterium smegmatis for infection with deoxyribonucleic acid (DNA) extracted from phage B1 was found in the late log phase of bacterial growth. This state of the culture was used in quantitative studies on the infectivity of the DNA. The buoyant density of B1 DNA was 1.728 g/cc in CsCl, and 1 mug of the DNA produced 84 infective centers, the phage equivalent of which was 1.5 x 10(-8). The infectivity was destroyed by catalytic amounts of deoxyribonuclease but not by specific B1 antiserum. Tween 80, which prevents phage adsorption, did not prevent DNA infection. The response of plaque-forming ability to DNA concentration suggested that two or more molecules are required to initiate an infective center. The low efficiency of DNA infection in mycobacteria was considered to be caused by a limiting population of competent cells in the culture employed; in this experiment less than 10(-5) of the cells were infected with DNA. A typical cycle of infection was observed, although the latent period was prolonged and the burst size reduced after DNA infection. The transition of B1 DNA infection to deoxyribonuclease insensitivity had a lag period of about 10 min, and increased linearly with a velocity of about 0.24 infective centers per min per mug of DNA. Half of the infective titer was inactivated by heating at 92 C for 15 min. The melting temperature was about 96 C. Species barriers were not crossed by B1 DNA; however, the DNA was infectious for a B1-resistant mutant of the host.

ADSORPTION OF INFLUENZA A VIRUS BY AEROBACTER AEROGENES SPHEROPLASTS

Brown, Ronald J. (University of Kansas, Lawrence), Albert A. Benedict, and Nancy Armstrong . Adsorption of influenza A virus by Aerobacter aerogenes spheroplasts. J. Bacteriol. 83: 1124–1130. 1962.— Aerobacter aerogenes spheroplasts adsorbed virus at a greater rate than whole A. aerogenes cells or cell-wall preparations. The largest fragments of sonic-disrupted spheroplasts were responsible for adsorption. Adsorption was characterized by rapid disappearance of viral hemagglutinin in about 8 min, elution of hemagglutinin, and followed again by complete adsorption of hemagglutinin. Viral activity was not recovered from spheroplasts after the final adsorption phase. Spheroplasts treated with heat, dilute periodate, or formaldehyde did not adsorb virus, and treatment of spheroplasts with receptor-destroying enzyme resulted in delayed adsorption.

Importance of Genetics of Viruses in Medical Research

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The protein coats or ghosts of coli phage T2. II. The biological functions

Phage coats or ghosts, composed entirely of protein, appear to be responsible for protecting the phage nucleic acid from degradation by factors in the surrounding medium; attachment of the virus to its susceptible host; and delivering the nucleic acid to the interior of the cell. In addition, the ghosts have a number of biological actions which resemble similar actions of the parent phage. Thus, they both "kill" cells, inhibit pentosenucleic acid formation, interfere with subsequent infection by other virus particles, block adaptive enzyme formation, induce or trigger lysis of the host, and cause a leakage of phosphorus-containing fragments from the cell. Results to date fail to demonstrate a direct involvement of the ghosts in the passage of genetic information to the progeny. Several of the above changes induced in the host cell following attachment of ghosts could be derived from an alteration in but a single metabolic reaction. The stoichiometry of the ghost-bacterial cell interaction is different from that of the parent phage. Experiments to distinguish between a variable response of the host cell to reaction at different sites and a state of heterogeneity in the ghost preparations suggest the former but they are not decisive.