- Volume 126, Issue 2, 1981
Volume 126, Issue 2, 1981
- Biochemistry
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Simultaneous Assay of Dihydroxyacetone Synthase and Transketolase in a Methylotrophic Yeast Grown in Continuous Culture. A Cautionary Note
More LessThe methylotrophic yeast Candida boidinii CBS 5777 was grown in continuous culture under carbon limitation on glucose, glucose plus methanol, and methanol as carbon and energy sources. During adaptation from glucose to methanol there was a rapid rise in the specific activities of triokinase, fructose-1,6-bisphosphatase and dihydroxyacetone synthase, which are key enzymes of the xylulose phosphate cycle of formaldehyde fixation. The specific activity of classical transketolase fell during this adaptation.
Extracts from carbon-limited C. boidinii contained an enzyme which catalysed oxidation of NADH when some preparations of ribose 5-phosphate were added, which was not a transketolase. This enzyme activity was dependent on an impurity in such ribose 5-phosphate preparations and can be confused with transketolase activity.
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Effects of Inhibitors on Mitochondrial Adenosine Triphosphatase of Tetrahymena pyriformis ST
More LessMitochondrial adenosine triphosphatase (ATPase) of the ciliate protozoon Tetrahymena pyriformis ST is completely inhibited by antiserum prepared against F1-ATPase purified from Schizosaccharomyces pombe, and by naturally occurring inhibitor proteins from this yeast and from bovine heart mitochondria. An ATPase inhibitor protein is also present in extracts of T. pyriformis. Mitochondrial ATPase of T. pyriformis is only partially inhibited by the F0-ATPase inhibitors N,N′-dicyclohexylcarbodiimide, oligomycin, leucinostatin, triethyltin sulphate and venturicidin, and (at high titres) by the F1-ATPase inhibitors Dio-9, efrapeptin, 4-chloro-7-nitrobenzofurazan and spegazzinine. Aurovertin, citreoviridin and quercetin were not inhibitory. Resistance to inhibitors distinguishes this mitochondrial ATPase from all those previously examined.
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Microbiological Oxidation of Steroid Hydrocarbons
More LessFungal and bacterial oxidation of steroid hydrocarbons has been examined. A rapid assay method for detection of metabolites derived from 5α-[4-14C]cholestane is described. Out of 87 organisms tested, 16 gave isolable oxidation products, while others degraded the hydrocarbon without producing stable intermediates. Preliminary characterization of these compounds is based on chromatographic properties.
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The Reaction of Cytochrome o in Escherichia coli K12 with Oxygen. Evidence for a Spectrally and Kinetically Distinct Cytochrome o in Cells from Oxygen-limited Cultures
More LessIntact cells harvested from O2-limited batch cultures of Escherichia coli K12 contained high levels of the CO-binding cytochromes d, o and a 1. In photodissociation difference spectra (i.e. photolysed minus reduced + CO), a peak at 436 nm and a trough at 415 nm have been assigned to an o-type cytochrome, and not cytochrome d, by photolysis with white light and an He-Ne laser. The reaction of reduced cytochrome o 436 with O2 at sub-zero temperatures involved O2 binding to give intermediate(s) with spectral characteristics similar to those of the reduced oxidase-CO complex. The reaction with O2 at successively higher temperatures (range − 98 to − 59 °C) was accompanied by the formation of a trough (with reference to the CO-liganded state) at 436 nm which eventually shifted to 432 nm, indicative of the oxidized form. The apparent energy of activation at low temperatures was 446; kJ mol−1 (107; kcal mol−1). There was a linear relationship between the rate of formation of the oxygen compound and the O2 concentration up to about 0·5; mm. The second-order constant for this reaction was 109; m−1 s−1 at -100C, at least 10-fold greater than for the reaction of cytochrome o 432 with O2 in cells from vigorously aerated cultures. The reaction of both types of cytochrome o with O2 was not readily reversible in the light or in the dark and was further distinguished from the reaction with CO by the markedly lower velocity of the CO reaction. Comparisons are drawn between the reactions with O2 of cytochrome(s) o in E. coli from O2-sufficient and O2-limited cultures and of mitochondrial cytochrome a 3. It is proposed that, like the synthesis of cytochrome d, the formation of cytochrome o 436 represents an adaptation of the organism to reduced O2 availability.
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Changes in Density of Mitochondria and Glyoxysomes from Neurospora crassa: a Re-evaluation Utilizing Silica Sol Gradient Centrifugation
More LessThe buoyant density of isolated mitochondria and glyoxysomes obtained from Neurospora crassa grown under different conditions was investigated by density-gradient centrifugation on Percoll. Mitochondria isolated from N. crassa in the exponential phase of growth with sucrose as the carbon source were more dense (1·077; g ml−1) than those isolated from hyphae in the stationary phase (1·069; to 1·073; g ml−1). A second population of mitochondria (density 1·059; to 1·061; g ml−1) was also present in the stationary phase. When N. crassa was grown with acetate as the carbon source, mitochondria isolated from hyphae in the exponential phase of growth were found to be less dense (1·079; g ml−1) than those present in the stationary phase (1·089; g ml−1). The glyoxysomes were found to be less dense than the mitochondria and their density decreased from 1·076; to 1·055; g ml−1 as the hyphae aged.
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The Oxidation of Tricarboxylate Anions by Mitochondria Isolated from Neurospora crassa
More LessMitochondria isolated from Neurospora crassa grown with sucrose as the sole source of carbon and energy oxidized citrate and cis-aconitate at high rates, and showed good respiratory control and high ADP/O ratios. The oxidation of both substrates was inhibited strongly by rotenone but only slightly by malonate. In contrast, isocitrate was oxidized slowly, with poor respiratory control. Treatment with detergent showed that both NAD+- and NADP+-isocitrate dehydrogenases were situated within the mitochondrial matrix. It thus appeared that the rate of oxidation of exogenous isocitrate was limited by a slow rate of translocation across the inner mitochondrial membrane.
When N. crassa was grown in an acetate-containing medium, the mitochondrial pellet, prepared by differential centrifugation, catalysed a rapid oxidation of isocitrate and contained a high activity of isocitrate lyase. The oxidation of isocitrate and succinate was strongly inhibited by malonate but only slightly by rotenone. Density-gradient centrifugation revealed that the apparent oxidation of isocitrate by mitochondrial pellets was due to contamination by glyoxysomes. Isocitrate was converted into glyoxylate and succinate in the glyoxysomes, then succinate was translocated across the inner mitochondrial membrane and oxidized by the respiratory chain.
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Isolation and Characterization of a Unique Serine Protease from Bacillus cereus Spore Coats
More LessA protease associated with spore coats of Bacillus cereus was extracted with 25 mM-dithioerythritol plus 2 M-urea at pH 9·0; and purified by ammonium sulphate fractionation and affinity chromatography. The spore protease differed from two intracellular proteases in pH optimum, pH stability, heat stability, stability in the presence of dithioerythritol and urea, molecular weight and in lack of reactivity with antibody to one of the intracellular proteases. The distinctive nature of the spore protease was also suggested by the fact that in a mutant with an altered intracellular protease, the properties of the spore protease remained unchanged. Inhibitor studies suggested that the spore protease was of the serine type with some similarities to trypsin. Two mutants were isolated with altered heat and pH stabilities of the spore protease; the intracellular proteases were unaltered. Spores produced by the mutants contained the same amount of coat protein per spore as the wild-type and germinated as well as the wild-type.
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- Ecology
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Promotion and Inhibition of Soil Aggregate Stabilization by Micro-organisms
More LessMicrobial cells in suspension were added to two soils. After drying, the degree of aggregation and stability of the aggregates to water was estimated by adding water, shaking and measuring turbidimetrically the particles remaining in suspension. In a silt loam (Hamble series), Azotobacter chroococcum, Lipomyces starkeyi and Pseudomonas sp. all promoted the stabilization of aggregates, this being related to the number of cells added, but Mucor hiemalis inhibited the process. In a clay soil (Denchworth series), Mucor hiemalis and Pseudomonas sp. both promoted stabilization. The stabilization of the silt loam by Lipomyces starkeyi was also produced by the polysaccharide extracted from the cell.
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Degradation of Bacteria by Agaricus bisporus and Other Fungi
More LessAgaricus bisporus and other fungi (Basidiomycetes, Ascomycetes, Fungi Imperfecti and Phycomycetes) grew and produced transparent zones in opaque media containing killed Bacillus subtilis as sole carbon and nitrogen source. Other Gram-positive and Gram-negative bacteria were also degraded by A. bisporus. Degradation of B. subtilis by A. bisporus was examined by light and electron microscopy. Liquid cultures were assayed for extracellular fungal enzymes which included β-N-acetylglucosaminidase, lipase, nucleases and acid, neutral and alkaline proteases.
Microbial biomass in compost may serve as a source of nitrogen, carbon and minerals, and as a water reserve for the growth of A. bisporus.
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- Genetics And Molecular Biology
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A Conjugative ‘Plasmid’ Lacking Autonomous Replication
More LessAttempts were made to isolate open and covalently closed circular DNA from strains containing the IncJ plasmids. All of the methods tried were unsuccessful. It was shown that the IncJ plasmid R391 can integrate into the Escherichia coli K12 chromosome and can mobilize chromosomal markers from a single origin in an orientated manner. It is proposed that the IncJ plasmids are integrated in the chromosome for most, if not all, of their existence and this explains the inability to isolate plasmid DNA from strains containing them.
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Selection for Increased Penicillin Titre Following Hybridization of Divergent Lines of Aspergillus nidulans
More LessSexual hybridization of two divergent lines of Aspergillus nidulans, which had been selected for increased penicillin titre through successive cycles of mutagenesis, released considerable variation for this character. The recovery of segregants with titres equivalent to that of the unselected ancestor suggested that mutations in different genes had been selected in the two lines. However, complementary segregants with substantially improved titres were not found, indicating interactions, probably of a duplicate nature, among the induced mutations. All the genetic variation released by hybridization was fixed following two generations of selection for high titre, but only a small gain over the initial selection lines was achieved. Hybridization of divergent strains has been widely advocated as a means of strain development. The failure to achieve the anticipated gains in this programme is attributed primarily to the unfavourable interactions amongst the induced mutations. Whether similar interactions occur generally in crosses between strains selected by mutagenesis remains to be established and will be an important factor in determining the contribution of recombinational approaches to yield improvement.
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Characterization of Bacteriophage j2 of Salmonella typhi as a Generalized Transducing Phage Closely Related to Coliphage P1
K. Mise, M. Kawai, Y. Yoshida and A. NakamuraPhage j2, a lysogenic phage in Salmonella typhi J2, was shown to produce tiny plaques on various Vi type strains of S. typhi, to be a generalized transducing phage, and to have many characteristics including a serological one in common with phage P1 of Escherichia coli. Lysogenization of various S. typhi type strains with j2 or P1-group phages usually resulted in the alteration of the phage types of the S. typhi strains, except that phage j2 did not cause alteration of type 53. Phage j2 transduced, at high frequencies, much larger DNA molecules (up to at least 70 megadaltons) than those known to be transduced by Salmonella phage P22: this should prove useful for the genetic analysis of S. typhi.
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Hydrogen Autotrophy as a Transferable Genetic Character of Nocardia opaca 1b
M. Reh and H. G. SchlegelA mating system to transfer the ability of growing autotrophically as a hydrogen bacterium (aut + marker) has been developed in Nocardia opaca strain 1b. Following filter mating between an aut + trp str strain and an aut strain, transconjugants of the phenotype Aut+Trp+Strs were obtained. The number of recombinant colonies exceeded the number of revertants by a factor of 105. This and other crosses indicated that only the aut + marker is transferred. Among other markers tested (growth on lactate and benzoate) no new combinations were found. A few strains of the Rhodococcus taxon were tested for their ability to act as recipients. Transconjugants of Rhodococcus erythropolis and Corynebacterium hydrocarboclastus able to grow autotrophically were isolated. Most transconjugants were able to act as aut + donors, but with different recipient spectra. As indicated by the observation of sectored colonies after autotrophic growth, by the measurement of the frequency of loss of autotrophy compared to auxotrophic markers, and by the effect of mitomycin C treatment, the aut + marker does not become integrated in the recipient chromosome in a stable state. It is probably located on a plasmid.
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Phage X: A Plasmid-dependent, Broad Host Range, Filamentous Bacterial Virus
More LessPhage X was isolated from sewage as plating on Escherichia coli or Salmonella typhimurium strains harbouring the incompatibility group X plasmid R6K. It also plated on a strain of Serratia marcescens carrying this plasmid. It failed to form plaques on Proteus mirabilis, P. morganii or Providencia alcalifaciens harbouring R6K, but did multiply on them. No phage increase occurred with homologous R− strains. Phage X also plated or registered an increase in titre on E. coli or S. typhimurium strains carrying various plasmids of incompatibility groups M, N, P-1, U or W as well as the unassigned plasmid R775. It adsorbed to pili determined by a group P-10 plasmid in a Pseudomonas aeruginosa strain but did not multiply on this organism. The phage was filamentous and curly, resistant to ribonuclease and diethyl ether and sensitive to chloroform. It adsorbed to the tips of pili.
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Phage t: A Group T Plasmid-dependent Bacteriophage
More LessPhage t was isolated from sewage from Pretoria. It formed plaques only on Escherichia coli and Salmonella typhimurium strains that carried plasmids belonging to incompatibility group T. Five of six group T plasmids permitted visible lysis of R+ host strains. There was no visible lysis of E. coli J53-2 or S. typhimurium LT2trpA8 carrying the T plasmid Rts1 although the strains supported phage growth as indicated by at least a 10-fold increase in phage titre. The latter strains transferred the plasmid at high frequency to E. coli strain CSH2 and the resulting transconjugants plated the phage. Proteus mirabilis strain PM5006(R402) failed to support phage growth although it transferred the plasmid and concomitant phage sensitivity to E. coli J53-2. The phage was hexagonal in outline, RNA-containing, resistant to chloroform and adsorbed to the shafts of pili determined by T plasmids.
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Phage F0 lac: An F0 lac Plasmid-dependent Bacteriophage
More LessBy enriching sewage with Escherichia coli or Salmonella typhimurium strains harbouring the plasmid EDP208, a constitutive pilus-producing derivative of plasmid F0 lac, a phage was isolated which plated on these two organisms but not on isogenic strains without the plasmid. The phage was named F0 lac; it had a hexagonal outline with a diameter of 28 nm, contained RNA, was resistant to chloroform, and probably adsorbed preferentially to the sides of EDP208 pili very near the tip. Phage multiplication could be demonstrated on E. coli or S. typhimurium strains carrying the plasmid F0 lac, but an increase in titre did not occur on E. coli strains carrying plasmids of the F complex. Results of phage multiplication experiments on strains carrying the depressed pilus-producing plasmids R71 or TP224-Tc, which determine pili serologically related to those of EDP208, were inconclusive. Phage F0 lac was found to be serologically related to phage UA-6. another isolate specific for EDP208.
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Is the IS 1-flanked r-Determinant of the R Plasmid NR1 a Transposon?
More LessThe 23 kilobase multiple drug resistance r-determinant (r-det) of the R plasmid NR1 is an IS1-mediated transposon, Tn2671. Drug-resistant Escherichia coli transductants isolated after infection with bacteriophage P1::Tn2671 derivatives carry the intact r-det in their chromosomes. Independently isolated transductants carry the r-det at different locations on the chromosome. From the E. coli chromosome, Tn2671 can transpose to various locations on the phage P7 genome. Throughout these processes, r-det is maintained as a stable unit. Various possible molecular mechanisms, which all might contribute with characteristic frequencies to the transposition of Tn2671, are discussed. The results presented are relevant to the understanding of mechanisms for a wide spreading of drug resistance genes.
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Genetic Studies of the Fertility Plasmid SCP2 and its SCP2* Variants in Streptomyces coelicolor A3(2)
More LessThe plasmid SCP2, initially discovered through the occurrence of a high fertility variant, SCP2*, is a self-transmissible fertility factor capable of promoting chromosomal recombination within Streptomyces coelicolor A3(2). Further high fertility variants of SCP2, similar to SCP2*, were isolated from amongst the recombinants produced in matings involving SCP2, and their genetic properties were compared. SCP2 and its derivatives elicit lethal zygosis on transfer into an SCP2− recipient; this plasmid-determined phenotype allowed the isolation of SCP2− strains and the detection of the interspecific transfer of SCP2* by mating from S. coelicolor to Streptomyces parvulus and Streptomyces lividans, whereupon it underwent stable maintenance. The transfer genes of SCP2 and SCP2*, which are not normally fully expressed, were shown to undergo transient derepression on entry into an SCP2− strain. An ‘entry disadvantage’ system determined by SCP2 and SCP2* was recognized.
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Genetic and Epigenetic Factors Involved in the Excretion of Naphthoquinone Pigments into the Culture Medium by Nectria haematococca
More LessThe production by the fungus Nectria haematococca of antibiotic pigments related to fusarubin can be increased by (i) culture conditions unfavourable for good growth, (ii) multiplication of two cytoplasmic factors of unknown molecular nature, and (iii) mutation of nuclear genes. Six nuclear genes involved in the regulation of naphthoquinone release have been characterized and mapped. Some have three allelic forms: the wild allele, one or several mutated alleles determining the hyperproduction of pigments, and one or several intragenic suppressors of the latter mutations. These genes also seem to be involved in developmental events, especially in sexual reproduction.
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Bacteriophage-induced Sporulation in Bacillus cereus T
More LessAn oligosporogenic strain of Bacillus cereus T was found to carry an inducible phage. CsCl-ethidium bromide gradients of lysates of this strain contained satellite DNA of the same density as the phage genome. Neither the phage nor the satellite DNA could be detected in the sporogenic parental strain. Purified phage preparations increased sporulation from 10-50-fold when added to cultures of the oligosporogenic strain.
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- Immunology
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Immunochemical Studies on the Cell-wall Antigen of Group B Streptococcus, Type Ib
More LessA Polysaccharide antigen of group B streptococcus type Ib was extracted from sodium dodecyl sulphate-treated cell walls by trichlorocetic acid. In crossed immunoelectrophoresis the polymer reacted with specific antisera to serotypes. Ia, Ib and Ic of group B streptococci and with commercial grouping antiserum to give one preciptin line. However, the antigen did not react with antisera to types II and III. The evidenc suggests that this polymer confers the group specificity to Ib of group B streptococci. The polysaccharide, after purification on DEAE-cellulose, was shown to consist of rhamnose, glucosamine, galactose, glucose, sialic acid and a trace of phosphorus.
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- Medical Microbiology
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Identification of Ureaplasmas from Cattle Using Antisera Prepared in Gnotobiotic Calves
More LessAntisera were prepared in gnotobiotic calves to three bovine ureaplasma strains which were selected as representatives of the three clusters of serologically similar, but not identical, strains recognized in previous experiments with rabbit antisera. A further 110 isolates from various organ systems of cattle from six countries reacted by the fluorescent antibody technique with at least one of these bovine antisera and it appears that bovine ureaplasmas can be identified and classified by means of three antisera only. It is suggested that the bovine ureaplasmas could be designated as groups A, B or C, these being further subdivided with rabbit antisera. These findings make possible the screening of cattle for antibody to ureaplasmas with just three antigens and also have implications for immunization.
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- Physiology And Growth
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Glycollate Metabolism in the Obligate Chemolithotroph Thiobacillus neapolitanusGrown in Continuous Culture
More LessCO2-limited chemostat cultures of Thiobacillus neapolitanusexcreted 13·5; nmol glycollate min−1 (mg protein)−1. This confirmed the earlier finding that glycollate excretion by T. neapolitanusis dependent on the CO2/O2 ratio applied in the chemostat and thus is probably due to the oxygenase activity of d-ribulose-1,5-bisphosphate (RuBP) carboxylase. RuBP-dependent oxygen uptake and activity of phosphoglycollate phosphatase were demonstrated in cell-free extracts of T. neapolitanus.
Thiobacillus neapolitanuswas able to metabolize exogenous glycollate only to a limited extent. The proportion of dry weight that was derived from [1-14C]glycollate by both CO2- and thiosulphate-limited chemostat cultures was only 0·7 % of the total. Short-term labelling experiments with [1-14C]glycollate and enzyme studies indicated that T. neapolitanuscan metabolize glycollate via two pathways. The enzymes of the glycine-serine pathway were demonstrated in cell-free extracts, but on the basis of kinetic experiments it was concluded that this pathway does not play a major role in glycollate metabolism. Malate was the major primary labelling product. Glyoxylate, formed from glycollate, may be incorporated into malate via malate synthase, which was detected in cell-free extracts of T. neapolitanus.
The activities of the enzymes needed for the metabolism of glycollate were independent of growth conditions applied in the chemostat. The results are discussed in relation to the possible causes of obligate chemolithotrophy.
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Synthesis of 1,3-β-Glucanase and β-N-Acetylglucosaminidase during Autolysis of Neurospora crassa
More LessThe synthesis of 1,3-β-glucanase, β-N-acetylglucosaminidase and total protein was studied during autolysis of Neurospora crassa. Evidence for de novo protein synthesis during autolysis was obtained from the incorporation of [3H]tryptophan and [3H]phenylalanine into the protein pool and from the inhibitory effects of cycloheximide and puromycin. Glucose accumulated in the growth medium during autolysis and N-acetylglucosamine and two unidentified oligosaccharides were detected towards the end of the 46 d autolysis period. During autolysis, 1,3-β-glucanase accumulated in the medium to tenfold greater activities than β-N-acetylglucosaminidase. The former enzyme had a pH optimum of 5·5; and a K m of 0·45 mm. It was inhibited by excess substrate but not by excess glucose.
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Simultaneous Short-term Uptake of Nitrate and Ammonium by Oscillatoria agardhii Grown in Nitrate- or Light-limited Continuous Culture
More LessThe cyanobacterium Oscillatoria agardhii Gomont was grown in continuous culture under nitrate- or light-limited conditions. Short-term uptake rates of nitrate and ammonium were studied at various concentrations of nitrate and ammonium, both of which were present during the short-term assay. In nitrate-limited O. agardhii, the short-term ammonium uptake rate was not influenced by the presence of nitrate. Ammonium inhibited the rate of nitrate uptake in a non-competitive manner. An equation was derived for the short-term nitrate uptake rate which was a function of the ambient concentrations of both nitrate and ammonium. For a low ammonium concentration tested, the pattern of the nitrate-ammonium interaction in light-limited O. agardhii did not differ greatly from that found in nitrate-limited O. agardhii.
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Induction of Fenarimol-efflux Activity in Aspergillus nidulans by Fungicides Inhibiting Sterol Biosynthesis
More LessFungicides inhibiting sterol biosynthesis belong to chemically distinct classes such as imidazole, morpholine, pyridine, pyrimidine and triazole derivatives. Incubation of mycelium of Aspergillus nidulans for 90 min with representatives of these fungicides induced an efflux activity which prevented accumulation of fenarimol, a pyrimidine derivative, into the mycelium. Induction of this efflux activity reduced the fungitoxicity of fenarimol. Addition of oligomycin to mycelium in which fenarimol-efflux activity was induced immediately increased the uptake of fenarimol, indicating that the efflux activity is energy-dependent. Subsequent disruption of membrane permeability with sodium lauryl sulphate instantaneously caused leakage of fenarimol from the mycelium into the medium. The ability to induce fenarimol efflux is rather specific for inhibitors of sterol biosynthesis: except for pimaricin, fungicides with unrelated mechanisms of action did not have this ability.
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Nitrofurantoin Prompts the Stringent Response in Bacillus subtilis
More LessNitrofurantoin causes the stringent response in Bacillus subtilis. After exposure of a stringent strain to this drug, the intracellular concentrations of guanosine 3′-diphosphate 5′-diphosphate (ppGpp), guanosine 3′-diphosphate 5′-triphosphate (pppGpp) and ATP increased, while that of GTP decreased. In a relaxed strain no accumulation of ppGpp or pppGpp was observed, but both GTP and ATP declined after the addition of nitrofurantoin. Protein synthesis was equally sensitive to nitrofurantoin in both the stringent and relaxed strains, but the drug inhibited RNA accumulation only in the stringent strain, not in the relaxed strain. Nitrofurantoin also caused the accumulation of ppGpp in Escherichia coli and Serratia marcescens.
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- Short Communications
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Construction and Characterization of guaB-lacZ Fusions in Escherichia coli K12
More LessGuaB-lacZ fusion strains of Escherichia coli K12 have been constructed using the Casadaban (1976) gene-fusion technique. The major modification to the procedure was the removal of the guanine requirement of Mu-induced guaA auxotrophs by introduction of a ColEl-gua + plasmid prior to selection of the fusion. Conversion to prototrophy was necessary to overcome problems associated with repression of the gua operon by guanine added to selection media. Induction of the lysogenic fusion strains yielded plaque-forming λ transducing phages that carried the lac genes and either the complete guaB gene and the gua promoter or only a distal portion of guaB.
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Ultrastructure of a Gas-vacuolate Square Bacterium
More LessElectron micrographs are shown of the gas-vacuolate square bacterium found at the surface of a brine pool in Sinai. The bacteria have a thickness of 0·1; μm or even less in the central regions. Some are apparently surrounded by sheath material. They contain gas vesicles which are either spindle-shaped or cylindrical with conical ends, and up to 1 μm long. The bacterial surface has 20 nm subunits arranged in a regular array.
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Failure of Coagulase-negative Staphylococci to Transfer Antibiotic Resistance to Staphylococcus aureus 1030 in Mixed Cultures
More LessOne hundred and fifty-three isolates of coagulase-negative staphylococci obtained from human skin failed to transfer resistance to either cadmium ions (46 isolates), trimethoprim (37 isolates), erythromycin (25 isolates) or tetracycline (45 isolates) to Staphylococcus aureus strain 1030 or to each of 10 of its lysogenic derivatives in mixed cultures. Thirty-three trimethoprim-resistant coagulase-negative staphylococcal isolates obtained from the human intestine also failed to transfer this resistance to the recipients in mixed cultures.
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Isolation and Restriction Mapping of a Spiroplasma Plasmid
More LessA plasmid, pIJ2000, of approximately 7#x00B7;8 kilobase pairs (kb) and with a base composition of 22·4 mol% (G + C) has been isolated from the non-helical Spiroplasma citri strain ASP-1. pIJ2000 was the only covalently-closed circular DNA molecule detected in cleared ly sates of high passage cultures of strain ASP-1 following CsCl/ethidium bromide equilibrium buoyant density centrifugation. A primary isolate of strain ASP- 1 contained two additional plasmids of approximately 35#x00B7;4 kb and 14#x00B7;8 kb. pIJ2000 contained single sites for the restriction endonucleases BgZlII, HaeIII, HindIII and XhoI arid three sites for MboI.
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Glutamate Synthase Activity in Symbiotic Cyanobacteria
More LessGlutamate synthase (GOGAT) activities of the symbiotic cyanobacteria of the lichens Peltigera canina and Peltigera aphthosa and of the water fern Azolla caroliniana have been determined and, like glutamine synthetase (GS) activity, found to be substantially reduced compared with the activities found in the free-living cyanobacteria. A similar reduction in GOGAT activity was not noted in the symbiotic green alga (Coccomyxa sp.) in P. aphthosa. The selective reduction of GS-GOGAT activity in symbiosis may be related to the production of extracellular nitrogen by the symbiotic cyanobacterium.
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Activated Charcoal and Orientation Behaviour by Dictyostelium discoideum Slugs
More LessIncorporation of activated charcoal into the agar enhanced the accuracy of phototaxis by Dictyostelium discoideum slugs two- or threefold. This was due to absorption of stray light rather than adsorption of a phototaxis-impairing chemical. The presence of charcoal had no effect on thermotaxis, the critical cell density at which phototaxis and thermotaxis become impaired, Slug Turning Factor (STF) interference with phototaxis, or chemotaxis by slugs in STF gradients. Activated charcoal in the agar had other effects on D. discoideum which may be chemical in nature.
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Volume 97 (1976)
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Volume 96 (1976)
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Volume 95 (1976)
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Volume 94 (1976)
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Volume 93 (1976)
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Volume 92 (1976)
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Volume 91 (1975)
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Volume 90 (1975)
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Volume 89 (1975)
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Volume 88 (1975)
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Volume 87 (1975)
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Volume 86 (1975)
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Volume 85 (1974)
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Volume 84 (1974)
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Volume 83 (1974)
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Volume 82 (1974)
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Volume 81 (1974)
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Volume 80 (1974)
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Volume 79 (1973)
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Volume 78 (1973)
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Volume 77 (1973)
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Volume 76 (1973)
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Volume 75 (1973)
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Volume 74 (1973)
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Volume 73 (1972)
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Volume 72 (1972)
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Volume 71 (1972)
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Volume 70 (1972)
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Volume 69 (1971)
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Volume 68 (1971)
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Volume 67 (1971)
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Volume 66 (1971)
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Volume 65 (1971)
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Volume 64 (1970)
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Volume 63 (1970)
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Volume 62 (1970)
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Volume 61 (1970)
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Volume 60 (1970)
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Volume 59 (1969)
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Volume 58 (1969)
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Volume 57 (1969)
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Volume 56 (1969)
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Volume 55 (1969)
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Volume 54 (1968)
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Volume 53 (1968)
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Volume 52 (1968)
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Volume 51 (1968)
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Volume 50 (1968)
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Volume 49 (1967)
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Volume 48 (1967)
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Volume 47 (1967)
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Volume 46 (1967)
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Volume 45 (1966)
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Volume 44 (1966)
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Volume 43 (1966)
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Volume 42 (1966)
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Volume 41 (1965)
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Volume 40 (1965)
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Volume 39 (1965)
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Volume 38 (1965)
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Volume 37 (1964)
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Volume 36 (1964)
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Volume 35 (1964)
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Volume 34 (1964)
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Volume 33 (1963)
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Volume 32 (1963)
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Volume 31 (1963)
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Volume 30 (1963)
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Volume 29 (1962)
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Volume 28 (1962)
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Volume 27 (1962)
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Volume 26 (1961)
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Volume 25 (1961)
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Volume 24 (1961)
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Volume 23 (1960)
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Volume 22 (1960)
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Volume 21 (1959)
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Volume 20 (1959)
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Volume 19 (1958)
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Volume 18 (1958)
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Volume 17 (1957)
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Volume 16 (1957)
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Volume 15 (1956)
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Volume 14 (1956)
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Volume 13 (1955)
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Volume 12 (1955)
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Volume 11 (1954)
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Volume 10 (1954)
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Volume 9 (1953)
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Volume 8 (1953)
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Volume 7 (1952)
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Volume 6 (1952)
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Volume 5 (1951)
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Volume 4 (1950)
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Volume 3 (1949)
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Volume 2 (1948)
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Volume 1 (1947)