- Volume 70, Issue 3, 1972
Volume 70, Issue 3, 1972
- Development And Structure
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Ultrastructural Development of Stalk-producing Cells in Dictyostelium discoideum, a Cellular Slime Mould
More LessSUMMARY: Changes in the structure of the myxamoebae involved in the formation of the stalk of the fruiting body, or sorocarp, of Dictyostelium discoideum were investigated. Observed changes in the ultrastructure relating to cell differentiation include: (i) food vacuoles disappear and autophagic vacuoles take their place after cell aggregation; (2) an inclusion in the mitochondria disappears during the vegetative feeding stages; (3) the decrease in number of an electron-clear vacuole is coincident with the appearance of the ‘prespore’ vacuole in cells of the hind portion of the migrating pseudoplasmodium; (4) while the prespore cells diminish in size and their cytoplasm becomes electron dense during culmination, the myxamoebae destined to form cellular elements of the stalk swell and their cytoplasm finally disintegrates.
The slime coat that encircles the entire pseudoplasmodium remains after fixation and dehydration as a triple-layered membrane resembling cell membranes. At the start of culmination, the initial core of unwalled stalk-forming cells descends through the then vertically oriented cell mass. The polarization of cytoplasm in the horizontally oriented prestalk cells of the apical papilla is described, as well as the formation of the two-layered sheath around the stalk. The mass of so-called rearguard cells of the migrating pseudoplasmodium separates during culmination and a fraction of them form the basal disc while the remainder rise on the stalk just below the prespore mass.
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- Ecology
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The Microbial Flora of the Gut of the Pouch-young and the Pouch of a Marsupial, Setonix brachyurus
More LessSUMMARY: Bacteria were found in the alimentary tract of 40 pouch-young, ranging in age from 1 to 157 days, and within the marsupium of six adult females of Setonix brachyurus. Colonization of the neonate’s intestine occurred soon after birth; Escherichia coli and Streptococcus faecalis were frequently isolated from the intestines of pouch-young of all ages. Other micro-organisms present, but infrequently encountered, were Aerobacter aerogenes, Klebsiella sp., Salmonella newport, Pseudomonas aeruginosa and Staphylococcus albus. Protozoan cilliates were present in the stomachs of pouch-young older than 150 days.
The pouch of non-lactating and lactating adults harboured a variety of bacteria, but in one female expecting a birth the pouch flora was absent.
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- Genetics And Molecular Biology
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Isolation and Some Properties of Temperature-sensitive Mutants of Micrococcus radiodurans Defective in DNA Synthesis
More LessSUMMARY: Three temperature-sensitive mutants of Micrococcus radiodurans have been isolated which, unlike the wild-type, are unable to synthesize DNA at 39°. Synthesis of DNA stops immediately the bacteria are raised to the restrictive temperature. The mutants can be transformed normally for single genetic markers and can regain wild-type temperature resistance on incubation with DNA from wild-type at a frequency associated with single or very closely linked markers. Each mutant can also be transformed to wild-type temperature resistance with DNA from the other temperature-sensitive mutants. All three mutants are resistant to the lethal action of ionizing and ultraviolet radiations and at 39° are able to carry out all or most of the DNA repair functions associated with excision repair, but at a reduced rate compared with wild-type. The rate of excision at 39° of u.v.-induced thymine-containing pyrimidine dimers is four to five times slower in the mutants than in the wild-type.
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The Type b Capsulation Locus of Haemophilus influenzae: Map Location and Size
More LessSUMMARY: Capsulation of Haemophilus influenzae was investigated by genetic transformation with high-molecular-weight deoxyribonucleic acid. The DNA was extracted from a capsulated antibiotic-resistant strain of H. influenzae rd which had received the type b capsulation locus {cap b) by transformation. A non-capsulated polyauxotrophic derivative of strain rdwas used as recipient under conditions which permitted the Cap b transformants (assayed as iridescent colonies) to initiate multiplication promptly. The position of cap b on the H. influenzae chromosome map was established by use of chemically defined agar media selective for transformants which had received pairs of linked markers. The cap b locus lies between leucine and biotin loci, and shows about 80 % linkage to the bio-150 marker. The size of the DNA segment required for Cap b transformation was found by physical methods to be about 33 million daltons.
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Absence of Laccase from Yellow-spored Mutants of Aspergillus nidulans
More LessSUMMARYGreen-spored strains of Aspergillus nidulans contain a p-diphenol oxidase (laccase) which is only formed during sporulation and is absent from yellow-spored mutants. The enzyme was assayed colorimetrically using N,N-dimethyl-p-phenyl- enediamine as substrate. Other substrates oxidized were pyrogallol, gallic acid and 2,6-dimethoxyphenol. Quinol, catechol and p-cresol were not detectably oxidized. Experiments with a temperature-sensitive yellow-spored mutant showed that the yA locus of A. nidulans is a structural gene for at least a component of the enzyme, while indirect evidence suggests that the enzyme also contains copper. Yellow-green- spored mutants of the ygA locus produce an inactive enzyme whose activity can be restored by dialysis against copper salts. Under certain conditions the enzyme itself can diffuse from a wild-type colony to a yellow-spored mutant colony and there act to give green spore pigment. From this it is deduced that the normal site of action of the enzyme may be external to the cell membrane. A similar enzyme has also been found in conidiating cultures of Aspergillus niger and Penicillium brevicompactum.
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Two Modes of ‘Curing’ Transmissible Bacterial Plasmids
More LessSUMMARY: F′lac was efficiently eliminated by acridine orange from Escherichia coli k12, whether sex pilus synthesis was constitutive or repressed by anfi + R factor. R factors, F-like or I-like, repressed or derepressed, were not eliminated by acridine orange. Sodium dodecyl sulphate (SDS), known to eliminate certain plasmids determining constitutive synthesis of F pili, had no effect on cultures with wild-type (repressed) R factors. Bacteria with derepressed synthesis of pili, either F-like or I-like, but particularly the latter, showed increased sensitivity to SDS. SDS treatment selected from such cultures non-piliated cells, with lost or mutant R factors. Thus acridine orange was a true ‘curing’ agent, specific for F, whilst SDS acted only by selection of spontaneous variants.
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Host Ranges of R Factors
More LessSUMMARYAll R factors so far described can be transmitted to Escherichia coli. F-like R factors are transmissible to the Proteus group but not to the Pseudomonadaceae. Among, fi − R factors, I-like plasmids are not transferable to Proteus although they mediate conjugation, allowing transfer of other plasmids to this group. They are not transmissible to the Pseudomonadaceae. P-group plasmids are transmissible to both taxa. Plasmids of groups N and W are transmissible to Proteus (transfer to Pseudomonas was not tested because of lack of suitable markers).
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The Relationship between Filaments, Killing and Restoration in Irradiated Escherichia coli Strain B
More LessSUMMARY: The morphology of normal and 5-bromouracil (5-BU) containing Escherichia coli strain b was examined after exposure of the bacteria to X-rays (under aerobic and anoxic conditions) and to ultraviolet light (u.v.). The majority of filaments which developed after irradiation either originated a microcolony or disintegrated. Post-irradiation incubation with chloramphenicol (CMP) restored the ability of some of the bacteria to originate viable colonies by suppressing filament formation, particularly in the case of normal thymine-containing bacteria. CMP also prevented the disintegration of filaments, provided it was applied before they reached a critical length. This was particularly evident in 5-BU-containing bacteria. It is suggested that incubation with CMP may allow wall synthesis to proceed in the absence of protein synthesis, thereby enabling thickening of the wall to take place, so that normal division can resume on removal of the CMP.
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Methionine Regulatory Defects in Salmonella typhimurium Arising from Amber-suppressible Mutations
More LessSUMMARY: Cultures of 15 each newly isolated ethionine-resistant metJ and K regulatory mutants of Salmonella typhimurium were infected with an Escherichia coli F′lac episome with an amber (UAG) nonsense mutation in the lacZ gene. F′Lac+ ethio-nine-sensitive derivatives segregating Lac− bacteria were obtained from one metJ and one metK mutant. Genetical and physiological analysis showed that these derivatives had acquired amber suppressors active on the metJ and metK mutations, leading to the conclusion that the metJ and metK genes code for polypeptides. The possible roles of the metJ and K gene products are discussed in the light of these results.
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A Mutant of Escherichia coli with a Defect in Energy Metabolism
More LessSUMMARYA mutant of Escherichia coli with a decreased growth efficiency has been investigated. The results of growth studies with different substrates and of measurement of P/O ratios in membrane preparations suggest that the strain is defective in the ability to couple synthesis of ATP to electron transport.
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Non-smooth Mutants of Salmonella typhimurium: Differentiation by Phage Sensitivity and Genetic Mapping
More LessSUMMARY: Non-smooth mutants of Salmonella typhimurium strain lt2 with known lipo-polysaccharide (LPS) defects were tested for sensitivity to smooth-specific phages (P22 and P22h and a newly isolated phage, 9NA, active on P22 lysogens); Felix O phage; and several rough-specific phages including C21. Smooth strains were sensitive only to the smooth-specific and Felix O phages. Six rfb mutants (unable to make O chains) were sensitive to Felix O and all the rough-specific phages except C21 (pattern R-sens). Of nine rfa mutants (presumed to have LPS core defects) four were R-sens, six were resistant to Felix O and some rough-specific phages (pattern R-res-1), and one was also resistant to phage Br2 (pattern R-res-2). The phage sensitivity of phosphomannoisomerase (pmi) mutants was the same as that of rfb mutants, except that they were partly sensitive to P22h. UDPgalactose-epimerase-negative mutants were sensitive to C21 and various rough-specific phages including Br2 (pattern Epi-1). An rfc mutant (unable to polymerize O repeat units) was sensitive only to Felix O and P221 (pattern Zsr). A part-rough mutant of class D (with abnormally few O chains) was incompletely resistant to smooth-specific phages, resistant to Felix O but sensitive to all rough-specific phages except C21 (pattern D-1).
Spontaneous and mutagen-induced non-smooth mutants were isolated from lt2 strains with appropriate markers by selection with Felix O and/or P22 phage.(One parent strain used was non-lysogenic for Fels 2, for which lt2 wild-type is lysogenic. Lysogeny for Fels 2 did not affect sensitivity to the other phages.) Some mutants gave new sensitivity patterns. Mutants of these and of previously unmapped classes were crossed with smooth Hfr strains. The rfc loci of two mutants and pmi loci of two others were located in the gal-trp segment. Three mutants of pattern R-sens yielded O-specific hapten but mapped near his; they are believed to be unable to transfer O chains from antigen carrier lipid to the LPS core as a result of mutation at rfbT. Six mutants of pattern R-sens were smooth in cultural and serological properties; they mapped near his and are probably leaky rfb mutants. Many mutants had the class D part-rough phenotype, divisible by phage sensitivities into patterns D-1, D-2 and D-3. Mutants of all three classes mapped near xyl; they are likely to be rfa mutants, perhaps leaky, with LPS core defects which hinder but do not prevent attachment of O chains. Two classes were sensitive to C21 (Wilkinson & Stocker, 1968): rfaH mutants, of pattern Epi-1, unable to add the main-chain galactose unit of the core; and rfaG mutants, resistant to Br2 (pattern Epi-2), unable to add the proximal glucose unit. Both loci mapped in or near the strA-xyl-metA segment. Several non-smooth mutants did not grow in the presence of bile-salts. Three mutants (rfaF) made LPS deficient of the distal hep-tose unit; one mutant (rfaE) was unable to add the proximal heptose unit. Both these loci mapped in or near the strA-metA segment.
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- Physiology And Growth
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Effect of Long-chain Fatty Acids on Some Trypanosomatid Flagellates
More LessSUMMARY: A long-chain fatty-acid fraction obtained from the marine alga, Ulva lactuca, as well as decanoic, dodecanoic and hexadecanoic acids at levels of 250 μg/ml induced lysis of various Trypanosomatidae. However, octanoic and cis-9-octa-decenoic acids at higher concentrations had no effect. Decanoic, dodecanoic and hexadecanoic acids at levels below 100 μg/ml inhibited motility of the promasti-gotes of Leishmania donovani and L. tropica, and the epimastigotes and trypo-mastigotes of Trypanosoma cruzi. Crithidia fasciculata was relatively resistant to fatty acids and was not affected by decanoic acid at this level.
The lysis induced by the marine algal fatty acids and by decanoic and dodecanoic acids was preceded by the formation of rounded forms ofthehaemoflagellates which indicated the loss of membrane structure.
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Water Relations of Salmonella oranienburg: Accumulation of Potassium and Amino Acids during Respiration
More LessSUMMARYPotassium and 14C-labelled proline, aspartic acid, glutamic acid, and alanine were accumulated by Salmonella oranienburg, during glucose oxidation, over a range of water activity (a w) values. In the absence of amino acids, potassium accumulation increased to a maximum as a w was decreased to about 0·975 but then dropped to a low value at 0·960 a w; with an amino acid, potassium accumulation was much increased and maximum uptake occurred at 0·960 a w. [14C]Proline uptake increased linearly with decrease in a w, the accumulated proline being metabolized in part to glutamic acid and to deaminated compounds; at 0·95 a w uptake of [14C]-proline reached 1·4mmol/g dry bacteria. Uptake of aspartate was comparable to that of proline at a w down to 0·98 but then decreased. Relatively little exogenously supplied glutamate or alanine was accumulated at any water activity. At a w levels below 0·98, oxygen uptake by non-growing bacterial suspensions increased with time and accompanied the linear uptake of proline. Proline accumulation ceased when a maximum rate of oxygen consumption was reached. At 0·97 a w the rate of proline uptake was unaffected by a mixture of 19 amino acids, but the total proline uptake decreased to one-half. In contrast, the proline homologue azetidine-2-carboxylic acid lowered the rate and extent of proline accumulation by one-third.
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Physiology of a New Facultatively Autotrophic Thermophilic Thiobacillus
More LessSUMMARY: A new thermophilic thiobacillus (G+C = 66·2 mol %) has been isolated in pure culture. The temperature optimum for growth was 50°. Heterotrophic growth occurred on nutrient broth, but not on single organic compounds. No α-keto- glutarate dehydrogenase was present but unrestricted acetate incorporation took place via the glyoxylate cycle.
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- Short Communications
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- Taxonomy
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Isolation and Taxonomic Significance of Bacteriophages for Non-proteolytic Clostridium botulinum
More LessSUMMARY: Bacteriophages, lytic for wild-type strains of Clostridium botulinum and different from the phages that can be induced from these lysogenic cultures, were isolated from bottom sediments of an inland bay and its tributary river. The host ranges indicated seven phages, in three morphological groups: three were tailless phages, three had hexagonal head and sheathless flexible tail, and one had a sheathed tail. The hosts were restricted to non-proteolytic C. botulinum strains producing type B, E, or F toxin and to a few of the non-toxigenic clostridia which resemble C. botulinum type E. None of the phages was active on proteolytic C. botulinum producing type A, B, or F toxin or cultures producing type C or D toxin. The host ranges of the phages are considered to be part of the evidence that the C. botulinum types, as defined at present, based on the serological specificity of the toxins, obscure the natural relationships among the strains of the species.
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- Books Received
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- Corrigendum
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Volumes and issues
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Volume 170 (2024)
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