- Volume 18, Issue 2, 1958
Volume 18, Issue 2, 1958
- Article
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The Effect of the Medium on the Cultivation of Mycobacterium balnei at 37°
More LessSUMMARY: Mycobacterium balnei grows best at temperatures about 32°. Growth occurs at 37° only on certain media. The organism is more susceptible at 37° than at 32° to the inhibitory effects of oleic acid added to a simple defined medium. This appears to explain the failure of more complex media to support growth at the higher temperature.
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Development of the Culture of Streptomyces rimosus in Submerged Fermentation
More LessSUMMARY: The development of Streptomyces rimosus in submerged culture, in a medium containing starch, glucose, ammonium sulphate, corn-steep liquor and calcium carbonate, takes place in several phases which differ in their morphological and biochemical characteristics. The starting phase is characterized by the logarithmic growth of thick Gram-positive filaments of the primary mycelium. Nucleic acids and respiratory enzymes are being synthesized during this phase and free amino acids and inorganic phosphorus in the medium are being almost completely used up. A considerable amount of pyruvic acid is being produced and accumulated in the medium. No production of oxytetracycline and pigments takes place. In the phase of logarithmic growth the respiration of the culture reaches a maximum value of 500–700 ml. O2/l./hr.; at this stage growth of the primary mycelium ceases and its hyphae undergo fragmentation. Pyruvic acid, which had accumulated in the medium in the phase of logarithmic growth, is rapidly used up during the fragmentation period. From the fragments of the primary mycelium long Gram-negative filaments of secondary mycelium start growing. Growth in this phase is accompanied neither by any significant increase of the respiration nor by excretion of pyruvic acid; deoxyribonucleic acid (DNA) synthesis is considerably slower than in the phase of logarithmic growth and the total amount of ribonucleic acid (RNA) is decreasing; oxytetracycline and pigments are being produced both by the growing secondary mycelium and in the subsequent stationary phase.
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A Transduction-like Process within a Single Strain of Pseudomonas aeruginosa
More LessSUMMARY: A process of genetic transfer, which could be demonstrated with culture filtrates of a strain of Pseudomonas aeruginosa, is described. The evidence indicates that genetic material was transferred in association with a large particle and that the process was similar to Salmonella transduction except that in the present case it occurred spontaneously between mutants of a single strain.
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Poliovirus Mutants with Altered Responses to Cystine
More LessSUMMARY: Three strains of poliovirus (Akron, antigenic type 1; Brooks, type 2; Mabie, type 3), which require exogenously supplied cystine (or a cystine-substitute) for optimal cytopathogenic action on monkey kidney tissue cultures, were serially passaged ten times in cystine-deficient monkey kidney tissue cultures in tubes. From various passage levels in this system were isolated three mutants of Akron, four of Brooks and two of Mabie. These nine mutants are designated the cystine-response mutants and are distinguishable from their ancestral viruses used to initiate the passage series by being relatively cystine-non-requiring. Two criteria suffice to distinguish the mutants of any strain from each other: (1) the degree of loss of requirement for cystine, and (2) the degree of inhibition by relatively high concentrations of cystine. The compositions of the virus populations in most of the passage levels were determined, and from these determinations the patterns of emergence of the mutant viruses were delineated.
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The Properties of a Star Mutant of Phage T2
More LessSUMMARY: The properties of a plaque-type variant, or ‘star’ mutant, of coliphage T2 are investigated. This mutant forms sectored plaques which are composed of approximately equal numbers of the parental star phage particles and of rapid-lysing (r) mutants. The star mutant is shown to be a one-step mutant of wild-type, possessing a mutation at a locus, s 1, that is close to the r 1 locus of phage T2. The r mutants occurring in the star plaques are all double-mutants, containing as well as the s 1 mutation, a mutation at some further r locus. Rapid-lysing mutants isolated from different star plaques possess r mutations at different loci. The high proportion of r mutants occurring in the star plaques is due to selection of r mutants that are formed spontaneously during replication of the star phage. This selection occurs during phage multiplication in Escherichia coli that is no longer multiplying exponentially (old bacteria), but not in exponentially growing bacteria. The slow multiplication of star compared to r phage in old cultures of E. coli is not due to an inability of the old bacteria to synthesize star phage particles at the same rate as r phage particles, but is caused by two, probably related, factors. First, the star phage has a prolonged latent period in old bacteria, and secondly, the star phage particles that are eventually released when the old cells lyse re-adsorb very slowly to old bacteria in the culture. During multiplication in old bacteria the r phage therefore goes through many more cycles of growth than the s phage, and thus accumulates more rapidly.
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Three Star Mutants of Coliphage T2
More LessSUMMARY: Star mutants of coliphages produce irregularly-shaped plaques which harbour mixed phage clones consisting of two or more phage genotypes: one type which forms star plaques identical in morphology and genetic constitution to those of the primary star mutant and other types which form regular genetically-homo-geneous plaques. The peculiar morphology and genetic heterogeneity of star plaques is due to the appearance and subsequent selection in every such plaque of secondary mutants with growth properties superior to those of the primary star mutant. In the present work, the genetic structure of three such primary star mutants of coliphage T2 and of the secondary, regular mutants which they sport has been examined. The ‘bromouracil’ star mutant s 8 owes its star character to a single mutation at a locus s 8, which is not closely linked to any known genetic marker of coliphage T2. The secondary, regular mutants found in every plaque of s 8 harbour reverse mutations to s 8 + wild-type at the mutated star locus itself. The ‘extended-host-range’ star mutant h′ owes its star character to the h′ allele of the host range locus h. The secondary, regular mutants found in every plaque of h′ harbour suppressor mutations to h′ at a definite locus i 1 closely linked to h. These suppressor mutations abolish only the star effect of the h′ allele without affecting the extended-host-range conferred by h′ upon the coliphage T2. The ‘P32-decay’ star mutant hrs harbours a mutation rs which extends over a considerable sector of the T2 genome situated between the distantly linked loci r 7 and r 1. The star phenotype of this mutant derives from an interaction between the host-range locus h and the rs mutation so that some genetic states of the host range locus confer poor plaque development on phage particles in which they exist in conjunction with rs . The secondary, regular mutants found in every plaque of hrs harbour one of a set of non-allelic h + or ht mutations in the h locus, which abolish the plaque growth-inhibiting interaction of h with the rs mutation and which also affect the host range. It is possible to replace variable sectors of the rs mutation proximal to r 7 with their r + alleles by crosses of hrs to wild-type. One may suppose that star mutants should be encountered with all those plaque-forming virus types which can sport with sufficiently high probability, i.e. soon enough during the development of each plaque, secondary mutants of growth characteristics superior to those of the parent type.
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Turbidity Changes in Suspensions of Gram-Positive Bacteria in Relation to Osmotic Pressure
More LessSUMMARY: The turbidity of suspensions of Gram-negative micro-organisms is known to be influenced by the tonicity of the suspending medium. In contrast to this, suspensions of Gram-positive micro-organisms have the same optical density in 0·2 m-NaCl as in distilled water. At higher salt concentrations, however, occasionally some batches were found to display changes in turbidity. Correlation was shown between the concentration of the amino acid pool of the organisms and their response to changes in osmotic pressure of the suspending medium. Depletion of the amino acid pool resulted in an increase in the changes in turbidity, with the simultaneous suceptibility of Gram-positive bacteria to plasmolysis. A possible correlation between this optical effect and the separation of cytoplasmic membrane from the bacterial cell wall is discussed.
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Studies on the Antibacterial Activity of Certain Strains of Acetobacter
R. Steel and T. K. WalkerSUMMARY: A turbidimetric assay is described for antibiotic substances produced by Acetobacter acetigenum, NCIB 8132, and Bacterium xylinoides, NCIB 4940, based on the amount of inhibition of growth of a celluloseless mutant. Yield of antibiotic from each organism was independent of the source of nitrogen in the medium, but varied markedly with the carbon source and was highest when the organisms were grown for 10 days at 30° in a medium containing glucose (9 %, w/v), Difco yeast- extract (0·5 %, w/v) and peptone (Evans, 3 % w/v), in distilled water. Under these conditions growth of the assay organism was inhibited 50 % by filtrate diluted 1/44. The antibiotics were extremely alkali-labile being destroyed at 18° in 2 min. at pH 10. Activity of the filtrate from organism NCIB 8132 was not affected significantly by treatment with calcium carbonate, charcoal, cation- or anion-exchange resins, but was decreased by extraction at pH 3·0 with w-butanol, chloroform or methyl ethyl ketone. Activity of filtrate of organism NCIB 4940 was decreased by treatment with charcoal, cation- or anion-exchange resins and by extraction at pH 3·0 with benzene, n-butanol, chloroform, diethyl ether, ethyl acetate or methyl ethyl ketone.
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Ramycin: A New Antibiotic
More LessSUMMARY: A strain of Mucor ramannianus from Campine forest soil was found to secrete an antibiotic, for which the name Ramycin is proposed. It is especially active against Gram-positive micro-organisms and Myobacterium tuberculosis H37Rv, but sensitive organisms quickly acquire resistance to it. Although it is not very toxic, it possesses a necrotic action on tissues. Ramycin can protect mice against streptococcal and staphylococcal infections but not against H37Rv.
Ramycin crystallizes in orthorhombic plates. The new antibiotic is an optically-inactive unsaturated hydroxy acid, containing C, H and O only.
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An Outline of the Pattern of Bacterial Generation Times
More LessSUMMARY: The generation times of four species of organisms have been measured, each under several sets of conditions: Aerobacter cloacae, Serratia marcescens, Streptococcus faecalis and Pseudomonas aeruginosa. Minor variations in the experimental conditions appear to affect the mean generation time less in large samples than in small. This can be explained as a result of association between the generation times of closely related organisms. Positive correlation between the generation times of sisters, cousins and perhaps second cousins shows that the influence of an ancestor is felt through two or three generations. The observed correlation between mothers and daughters is usually small, probably because of bias due to the interval between fission of cytoplasm and fission of cell wall. The coefficient of variation of generation time is not a constant for the species but it is stable under given circumstances. It is possibly related systematically to the chemical complexity of the growth medium. In unhampered growth, less than 1 % of the organisms produced are non-viable. There is positive association between the viabilities of sisters, and between the viability of an organism and the generation time of its mother. The distribution of generation times can be represented by a Pearson Type III or else a Pearson Type V distribution; both are convenient in applications.
The generation time of an individual is considered to be determined partly by molecular accidents, partly by heredity.
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Observations on Phaeodactylum tricornutum
More LessSUMMARY: Phaeodactylum tricornutum Bohlin was isolated from a marine tank at Woods Hole, Mass., U.S.A. It appeared to be identical with the Plymouth strain of ‘Nitzsckia closterium forma minutissima’. Cells were of two characteristic types, oval and fusiform, each of which remained constant for many cell divisions in clonal culture. Triradiate cells arose rarely as atypical forms of the fusiform variety. Oval cells could arise as endospores within a fusiform cell. The transition from oval to fusiform was also studied, but details of the life cycle remain to be worked out. Electron micrographs showed the fusiform cells to be devoid of any organized siliceous structure, in agreement with previous observations. However, the oval cells were seen to possess a silica valve of a pennate diatom type, resembling those of the genus Cymbella. Only one valve was present on each cell, the remainder of the cell wall being vmsilicified. The valve was 6·2 μ. long, was equipped with a raphe, and was perforated by pores arranged in 60 striae. Oval and fusiform cells both contained approximately the same amount of silica (0·4–0·5 % dry weight). In each case, most of this silica could be recovered as a particulate fraction resistant to digestion in hot nitric acid. The silica obtained from oval cells was in the form of diatom valves, whereas that from fusiform cells consisted of irregular particles clearly not derived from broken silica walls.
Mucilaginous capsular material, soluble in hot water, represented 16 % of the dry weight of oval cells; it was absent from fusiform cells. Acid hydrolysis and paper chromatography indicated xylose, mannose, fucose, and galactose as components of the capsule.
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The Taxonomic Position of Phaeodactylum tricornutum
More LessSummary: A revised taxonomic description of Phaeodactylum tricornutum Bohlin is presented, with special emphasis on the details of the silica valve, a structure hitherto unobserved. The features distinguishing P. tricornutum from Nitzschia closterium (Ehr.) W. Sm., with which it has frequently been confused, are summarized. In view of the unique characters of P. tricornutum, it is proposed to establish within the Bacillariales a new suborder, the Phaeodactylineae, to which Phaeodactylum is assigned as the only known genus.
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Synergistic Morphogenesis by Mixtures of Dictyostelium discoideum Wild-type and Aggregateless Mutants
More LessSUMMARY: Aggregations involving mixtures of wild-type and ‘aggregateless’ mutant organisms of Dictyostelium discoideum were examined. The proportions of wild-type individuals which could initiate the formation of aggregative centres by their neighbours was found to depend markedly upon the particular mutant in the mixture. The mutants appear to have supplied some of the cells responding to the initiative stimulus where these were needed and also to have produced diffusible material enabling many more wild-type organisms to act as initiators than would ordinarily do so. The results also indicate the existence of a variety of cellular interactions which may underlie the normal morphogenetic sequence.
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Relationship between Beet Ringspot, Potato Bouquet and Tomato Black Ring Viruses
More LessSUMMARY: Serological and plant-protection experiments provided evidence that potato bouquet and beet ringspot viruses are strains of tomato black ring virus. Tomato black ring and potato bouquet viruses are more closely related to each other than either is to beet ringspot virus. The three produce similar symptoms and have a similar host range. There was no evidence that they are related to tobacco ring spot or peach yellow bud mosaic viruses. In the plant-protection tests, protection between serologically related virus strains often was not reciprocal; when protection was incomplete, the symptoms produced by the second virus were milder than those in plants infected by it alone. Strains of tomato black ring virus could be arranged in order of their ability to cause symptoms in plants already infected with other strains. Although results of the plant-protection and serological tests agreed broadly, the correlation was not complete, suggesting that the tests measure different properties of the virus particles. The degree of difference between strains of tomato black ring virus seems to reflect their geographical separation, something that is perhaps to be more expected with soil-borne than with other viruses.
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‘Restoration’ of Escherichia coli strain B After Irradiation: its Dependence on Suboptimal Growth Conditions
More LessSUMMARY: After irradiation of Escherichia coli strain B by ultraviolet or ionizing radiations, different plating media give rise to widely different viable counts; the surviving fractions are smallest on media which are optimal for the growth of unirradiated organisms. It is concluded that inhibition of colony formation after irradiation is due in part to an injury which leads to imbalance in the synthetic processes of the cell, so that ‘recovery’ or ‘restoration’ may be brought about by suboptimal conditions of growth. The proportion of cell deaths which may be ascribed to this particular injury is determined by the conditions obtaining in bacterial suspensions before and during irradiation, and also by the type of radiation used.
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