- Volume 57, Issue 1, 1969
Volume 57, Issue 1, 1969
- Article
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Some Properties of a Sporulating Bacillus subtilis Mutant Containing Heavy DNA
More LessSUMMARYA mutant (Cbl-1) was isolated from Bacillus subtilis 168 wild type (wt) sporulating cultures grown on nutrient agar. This mutant differs from the parental strain as follows. (1) In nutrient broth the mutant excretes a substance which kills the wt cells. Therefore when grown in a mixed culture (Cbl-1 plus wt), this property leads to a take-over pattern by the Cbl-1 mutant, and the spores obtained from such a culture are entirely of the mutant type. (2) The DNA of the Cbl-1 strain has a buoyant density in CsCl of 1·714g./cm.3 while that of the normal B. subtilis 168 is 1·703 g./cm.3 although both strains have a G + C content of 42 moles %. An explanation for the higher buoyant density of the Cbl-1 DNA has not yet been found. In addition to the base ratio data, transformation and transduction experiments indicate that Cbl-1 is a mutant of B. subtilis 168.
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A Kinetic Study of the Growth of Aspergillus nidulans and Other Fungi
More LessSUMMARYThe growth kinetics of Aspergillus nidulans, Mucor hiemalis and Penicillium chrysogenum on solid media and in submerged culture were studied. Growth of A. nidulans colonies on solid medium can be divided into the four phases of lag, exponential, deceleration and constant growth rate. The growth kinetics of A. nidulans in submerged culture were similar to those commonly found for unicellular micro-organisms. The effects on colony radial growth rate, of glucose concentration, medium depth, oxygen partial pressure and temperature were studied. The radial growth rate of glucose-limited colonies of A. nidulans increased linearly with the log. of the initial glucose concentration. The effects of glucose concentration on internode length, hyphal density and hyphal diameter were also studied. At glucose concentrations above 1 % (w/v) there was an inverse relation between the radial growth rate of A. nidulans colonies and their peripheral hyphal density. The relations between colony radial growth rate (Kr ) and germ tube specific growth rate (α g ) on solid media and specific growth rate in submerged culture (α s ) were investigated. Direct proportionality between Kr and α s of A. nidulans was found by varying specific growth rate by temperature changes. The germ tubes of A. nidulans conidia grew exponentially at a rate which was about 2·3 times as great as the specific growth rate of the organism in submerged culture. The colony radial growth rates of the three moulds could not be used as a measure of their relative specific growth rates in submerged culture.
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Action of Hydrogen Peroxide on Growth Inhibition of Salmonella typhimurium
More LessSUMMARYThe effect of hydrogen peroxide on the growth of Salmonella typhimurium lt2 in a mineral glucose medium was investigated. The H2O2 produced a lag period, the duration of which increased as the concentration of H2O2 in the medium was increased from 1 to 60 μg./ml. Growth subsequent to the lag period proceeded at the normal growth rate at concentrations of H2O2 as high as 30 μg./ml. Storage of H2O2 in the sterile growth medium resulted in a disappearance of H2O2 with a half-life of about 48 hr. The disappearance of H2O2 because of reaction with glucose resulted in proportionate decreases in the growth inhibitory action of the medium. Salmonella typhimurium destroyed H2O2 rapidly (half-time = 60 min.)–an effect attributed largely to bacterial catalase. The catalatic activity of the bacteria was decreased or eliminated by boiling or by treatment with cyanide. The growth of the bacteria in H2O2 resulted in the development of H2O2 resistance. By subculturing the wild type lt 2 in medium containing successively higher H2O2 concentration, a resistant strain designated lt2 p was isolated which grew in the presence of H2O2 concentrations that were completely inhibitory to the wild type.
The experimental results support the generally accepted conclusion that bacterial catalase acts in protecting the organism from H2O2. It is pointed out that in biological media H2O2 readily forms adducts with many compounds, including carbonyls, amino acids and thymine. Consequently, the inhibitory effects of H2O2, especially in studies involving auxotrophs, may be partly or wholly due to the peroxide adduct rather than ‘free’ H2O2.
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Dispersal of Streptomycetes in Air
More LessSUMMARYThe number of streptomycete propagules trapped from air above a fallow plot depended on the amount of dust in the air. Less than 20% of the propagules occurred as individuals; the remainder were mostly attached to the surface of airborne soil particles. Thus any action which disturbed the soil surface and launched soil particles into the air, such as the operation of an agricultural implement or a gusty wind, also increased the concentration of airborne streptomycete propagules.
With simulated rain, the first water drops which struck the soil surface launched both individual spores and spores attached to soil particles into the air; with time the water drops washed most propagules from the air.
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Light and Electron Microscopy of the Sheath of a Blue-green Alga
More LessSUMMARYLight microscopy observations of a Nostoc sp. of blue-green alga suggested that the sheath was comparable with the capsules of many bacteria. The sheath showed little internal differentiation under normal or phase-contrast illumination. It possessed a somewhat hazy outer margin from which portions sloughed off, it stained with Alcian blue and was probably polysaccharide. The sheath formed salt-like complexes with proteins at appropriate low pH values which rendered it visible by phase-contrast microscopy. The composition of the culture medium influenced sheath formation. Electron microscopy showed that the sheath consisted of a micro-fibrillar network containing small numbers of larger fibrils (about 200 Å in diameter) which was compressed into stria near to the cell wall and expanded into an open reticulum further out. It would appear to be formed by continuous secretion through the longitudinal walls of the trichomes, and as the outermost regions imbibed water the network structure expanded and finally sloughed off.
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The Electrokinetic Properties of Some Fungal Spores
More LessSUMMARYThe electrophoretic mobilities of conidia of Alternaria tenuis, Botrytis fabae, Penicillium expansum, Erysiphe graminis, Podosphaera leucotricha and Venturia inaequalis, basidiospores of Stereum purpureum, sporangia and encysted zoospores of Phytophthora infestans were determined in solution at various pH values. The spores all had characteristic and distinct pH-mobility curves. The zero mobility of P. infestans sporangia over the range pH 2 to 11 is consistent with a cellulose surface free from ionizable groups. The mobility of basidiospores of S. purpureum depended entirely on the presence of carboxyl groups. Chemical and enzymic treatments showed both amino and carboxyl groups on A. tenuis and B. fabae; phosphate was present in addition on P. expansum. The amino groups of ϵ-lysine, histidine and leucine contributed to the surface charge of B. fabae; amino acids and tyrosine were detected on A. tenuis. The surface of P. expansum was protein-free and the amino groups present were probably derived from a glucosamine or galactosamine polymer. Washed cell walls and intact conidia of B. fabae were electrophoretically similar but cell walls of P. expansum, unlike normal conidia, were phosphate-free. Mycelial ‘protoplasts’ of A. tenuis and Neurospora crassa and conidial ‘protoplasts’ of B. fabae had pH-mobility curves characteristic of a protein surface.
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The Biochemical Status of μ Particles in Paramecium aurelia
More LessSUMMARYμ particles of stock 540 (syngen 1) of Paramecium aurelia were isolated and studied. Electron microscopy showed that isolated μ particles were very similar to bacteria in fine structure, the general appearance being similar to that found by earlier workers. Contamination of the preparations with other cell particles and with the paramecium food bacteria was low. The isolated μ particles contained DNA, RNA, protein and probably carbohydrate and lipid. The DNA of the particles was characterized by density-gradient centrifugation in CsCl and by determination of Tm. The density of the DNA was estimated to be 1·694 g./c.c., a value very similar to that for the DNA of Paramecium aurelia 540 macronuclei, which was estimated to be 1·693 g./c.c. The Tm was likewise similar, being 82·0°, against 81·8° for Paramecium macronuclear DNA. However, this DNA was associated with the μ particle, as no such DNA could be prepared from genotypically identical P. aurelia which did not possess μ particles, and the DNA associated with the μ particles was not susceptible to DNase action on treatment of isolated μ particles with the enzyme before DNA extraction. Hence it seems that the μ particle has a membrane-protected DNA of a similar buoyant density to the P. aurelia DNA. Isolated μ particles possessed an active DNA-dependent system capable of the incorporation of ribonucleoside triphosphates into an acid-insoluble product. The reaction needed the presence of ATP, GTP, and UTP for optimal activity, and had an absolute dependence on Mg2+. The reaction was inhibited by actinomycin D, and a ribonuclease-sensitive product was synthesized.
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The Cause of Loss of Viability of Airborne Escherichia coli k 12
More LessSUMMARYThe uptake of uracil, pyruvate, methionine and oxygen and the breakdown of RNA and protein have been examined in Escherichia coli k 12 HfrC after storage as an aerosol for 15 min. in nitrogen at 80 % and 40 % relative humidity (RH). At 80 % RH there was greatest loss of viability and almost complete breakdown of RNA together with severe inhibition of energy production. At 40% RH all these effects were mitigated.
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The Cultivation of the Rumen Ciliate Entodinium simplex
More LessSUMMARYEntodinium simplex has been maintained in vitro anaerobically and in the presence of bacteria in a salts medium containing autoclaved rumen fluid, wholemeal flour and dried grass. The protozoa divided at least every 3 days during more than 2½ years. The wholemeal flour could be replaced by a mixture of rice starch and washed bran but not by either separately; in the presence of this mixture population densities of over 60,000 protozoa/ml. were obtained. Omission of the autoclaved rumen fluid decreased the number of protozoa to 25 % of this value. Evidence was obtained that it was the particulate matter in the rumen fluid that was an essential for growth.
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Septal Pores in Endomycopsis platypodis and Endomycopsis monospora
More LessSUMMARYIn ultra thin sections of hyphae of the yeast species Endomycopsis platypodis and E. monospora septal pores were observed with the electron microscope. The pores are enclosed by a swelling of the cross-wall. Electron-dense bodies plug the pores; these bodies are surrounded by a membrane which is connected with the endoplasmic reticulum and which also connects the plugs at both sides of the cross-wall via the pore.
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Split-dose Irradiation of Escherichia coli in the Absence and Presence of Mercaptoethylamine
More LessSUMMARYA single dose of γ-radiation to Escherichia coli b gave a semi-logarithmic dose-response curve. A second irradiation 3, 6, or 18 hr after a priming dose of 8 krad showed that the cells had become more radio-sensitive during the incubation between irradiations.
When mercaptoethylamine was present during irradiation, protection against the lethal effects of the γ-radiation occurred. After a priming dose to the bacteria in the presence of the radio-protective chemical, and incubations for 3,6, or 18 hr in its absence, a second irradiation in the absence of the chemical showed them to be much more radio-resistant than the normal unprotected Escherichia coli b. This indicates that the presence of the protector during irradiation alters the type of damage induced or the development and repair of that damage.
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Agglutinating Antigens of Lactobacillus jugurti atcc 521
More LessSUMMARYSerological studies were conducted on Lactobacillus jugurti (atcc 521) in an attempt to identify its agglutinating antigens.
Glycerol teichoic acid was isolated from the cell wall of atcc 521. Isolated wall teichoic acid removed 121 and 122 antibodies from atcc 521 antiserum, thereby demonstrating that it is an antigen involved in agglutination. 127 antibodies were not removed from antisera by the wall teichoic acid. Isolated atcc 521 cell walls did not agglutinate in anti-112 antiserum, nor did wall teichoic acid from the same organism react with this serum.
Intracellular teichoic acid of atcc 521 also removed agglutinating antibody from whole antisera. Gel double-diffusion experiments indicated that cell wall and intracellular teichoic acid are immunologically identical.
Lactobacillus jugurti (atcc 521) mucopeptide was prepared from the cell walls, and this component did not remove agglutinating antibody from antisera.
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Genetic Heterology between Escherichia coli k 12 and a Smooth Strain of E. coli
More LessSUMMARYcf 2004-6, a recipient strain, and 04m2, an Hfr donor strain of Escherichia coli 04:K(undetermined): H5, were used in mating experiments with E. coli k 12. 04m2 behaved like the k 12 donor strain in mating experiments. These donor strains genetically recombined with the k 12 recipient at higher frequencies than with cf 2004–6. The results of interrupted mating experiments were also more typical with the k 12 recipient than with cf 2004–6 in that there were sharp entry times for the markers studied and linear increases of recombinants with time. The possibility that host-controlled restriction decreased genetic recombination between E. coli k 12 and cf 2004–6 was pursued. We obtained no evidence for this possibility. Instead the data suggest that genetic heterology between these strains is affecting recombination. Genetic heterology also explains why 04m2 behaves more like a k 12 donor in mating experiments with cf 2004–6.
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Genetic Transformation in Rhizobium
More LessSUMMARYMutants of ground nut (Rhizobium cowpea group) strain GR3 were isolated using ultraviolet radiation and N-methyl-N′-nitrosoguanidine (NTG) as mutagenic agents. An adenine-requiring mutant was used as the recipient and its wild type as the donor in transformation studies. Initially minimal medium supplemented with 2 μg. adenine/ml. was used for the development of competence. The maximum transformation frequency was obtained after about 120 min. incubation. Supplementation of minimal medium with yeast extract and vitamin-free Casamino acids without the addition of adenine stimulated competence to a large extent. The competence was not further stimulated by any of the divalent ions used. The optimum DNA concentration for maximum transformation frequency was about 50 μg./ml.
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Antigenic Relationships Among Strains of Mycoplasma mycoides var. mycoides, M. capri and M. laidlawii Revealed by Complement-fixation Tests
More LessSUMMARYComplement-fixation tests were used to compare strains of Mycoplasma mycoides var. mycoides (5 strains), M. mycoides var. capri (5 strains) and M. laidlawii of bovine genital origin (3 strains). Strains of M. mycoides and M. capri showed cross-reactions of about 25% identity, but strains of M. laidlawii appeared to be antigenically distinct. The results, measured in terms of the amounts of complement fixed, are shown graphically and discussed in relation to the diagnosis of contagious bovine pleuropneumonia.
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