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  • 11
    Electronic Resource
    Electronic Resource
    Synchronization without oscillatory neurons (1996)
    Springer
    Biological cybernetics 74 (1996), S. 209-223 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Experimental results suggest that neurons in the cortex synchronize their action potentials on the millisecond time scale. More importantly this binding expresses functional relationships between the neurons. A model of neuronal interactions is proposed in which simultaneous discharges of neurons develop through specialized synaptic circuits. As an important prerequisite for this synchronization it is demonstrated that SynFire chains, generating different levels of excitation, propagate their activity waves at distinct velocities. Two chains were coupled by excitatory synapses and their activity was initiated at different times. Due to synaptic interactions, activity in the earlier-initiated chain accelerates propagation in the other chain until the two activity waves are synchronized. Compared with several neural network models with oscillatory units, physiologically more plausible neurons are simulated. It is still under debate whether neurons in the cortex show oscillatory dischargesper se. In particular, a high rate of noise relative to very weak synaptic gains cannot impair our results in the neural network simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652222
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  • 12
    Electronic Resource
    Electronic Resource
    Synchronization without oscillatory neurons (1996)
    Springer
    Biological cybernetics 74 (1996), S. 209-223 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract.  Experimental results suggest that neurons in the cortex synchronize their action potentials on the millisecond time scale. More importantly this binding expresses functional relationships between the neurons. A model of neuronal interactions is proposed in which simultaneous discharges of neurons develop through specialized synaptic circuits. As an important prerequisite for this synchronization it is demonstrated that SynFire chains, generating different levels of excitation, propagate their activity waves at distinct velocities. Two chains were coupled by excitatory synapses and their activity was initiated at different times. Due to synaptic interactions, activity in the earlier-initiated chain accelerates propagation in the other chain until the two activity waves are synchronized. Compared with several neural network models with oscillatory units, physiologically more plausible neurons are simulated. It is still under debate whether neurons in the cortex show oscillatory discharges per se. In particular, a high rate of noise relative to very weak synaptic gains cannot impair our results in the neural network simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652222
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  • 13
    Electronic Resource
    Electronic Resource
    Untersuchungen zum Säurestoffwechsel von Aspergillus niger (1966)
    Springer
    Archives of microbiology 53 (1966), S. 77-91 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Summary 1. Aspergillus niger has been grown from conidia at 30° C on a medium containing KNO3 as a single source of nitrogen. Influence of KNO3 concentration (i.e. C/N-relation) in the original medium on time course and yields of gluconic, citric, and oxalic acid accumulation has been investigated. KNO3 concentrations were between 1,0 and 0,01%. As the medium has been buffered by addition of CaCO3 and NaOH there was no influence of KNO3 concentration on pH. 2. Time course of accumulation of the three acids principally was the same with all concentrations: Related to flask yields of gluconic and citric acid decrease after some time, yields of oxalic acid remain constant after having reached a maximum value. 3. There has been an influence of KNO3 concentration in the original medium on velocity of accumulation and/or consumption of the three acids and on time and value of maximum yields related to flask and to glucose consumed. 4. Maximum yields related to flask and to glucose consumed reached a maximum value at 0.03–0.01% KNO3 with gluconic acid and at 0.125% KNO3 with citric acid. During the time glucose is not used up yields of oxalic acid have been highest at 1.0% KNO3. After this time yields have been highest at 0.125% KNO3.
    Notes: Zusammenfassung 1. Aspergillus niger wurde, ausgehend von Conidien, bei 30° C auf einer Nährlösung mit KNO3 als alleiniger Stickstoffquelle kultiviert. Es wurde untersucht, wie sich die KNO3-Konzentration und damit das C/N-Verhältnis in der Ausgangs-Nährlösung auf den zeitlichen Verlauf und die Stärke der Glucon-, Citronen- und Oxalsäureanhäufung auswirkt. Die KNO3-Konzentration wurde dabei zwischen 1,0 und 0,01% variiert. Ein Einfluß des KNO3-Angebotes auf den pH-Wert wurde durch Zusatz von CaCO3 und NaOH zur Kulturflüssigkeit verhindert. 2. Die Anhäufung der drei Säuren folgt bei allen KNO3-Ausgangskonzentrationen demselben Prinzip. Dieses besteht darin, daß der absolute Gehalt der Kulturen an Glucon- und Citronensäure nach Erreichen eines maximalen Wertes wieder abnimmt, der absolute Gehalt an Oxalsäure dagegen konstant bleibt. 3. Die KNO3-Ausgangskonzentration hat einen Einfluß darauf, mit welcher Geschwindigkeit die Säuren angehäuft werden bzw. wieder verschwinden, zu welchem Zeitpunkt ihr Gehalt absolut und auf den Glucoseverbrauch bezogenseinen maximalen Wert erreicht und wie hoch dieser ist. 4. Gemessen an den Maximalwerten des absoluten und des auf den Glucoseverbrauch bezogenen Säuregehaltes ist die Gluconsäureanhäufung am stärksten bei einer sehr niedrigen (0,03–0,01%) und die Citronensäureanhäufung bei einer mittleren (0,25–0,125%) KNO3-Ausgangskonzentration. Die Oxalsäureanhäufung hat ihr Optimum in der Zeit vor dem fast völligen Glucoseverbrauch bei 1,0%, danach bei 0,125% KNO3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00424742
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  • 14
    Electronic Resource
    Electronic Resource
    Untersuchungen zum Säurestoffwechsel von Aspergillus niger (1966)
    Springer
    Archives of microbiology 55 (1966), S. 81-90 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Summary Aspergillus niger has been grown from conidia at 43, 30 or 10° C on a medium containing glucose (5%) as a source of carbon and KNO3 (1%) as a source of nitrogen. Gluconic and citric acid have been added before and after glucose in the medium has been used up almost completely. By addition of each of the acids yield of oxalic acid related to flask could be increased. Yield of oxalic acid related to flask and to citric acid consumed depends on temperature and on time of addition. Incorporation of C14 from gluconate-C14 (U) and citric acid-1,5-C14 into oxalic acid has been demonstrated at 43° C for cultures having used up glucose almost completely. By this it is proofed that under these conditions gluconic and citric acid can be used as a source of carbon for accumulation of oxalic acid. It is suggested that increase of oxalic acid yield caused by addition of gluconic or citric acid is due to conversion of the two acids into oxalic acid (among other products) under all conditions investigated.
    Notes: Zusammenfassung Entwickelt sich das Mycel von Aspergillus niger ausgehend von Conidien bei 43, 30 bzw. 10° C auf einer Nährlösung mit Glucose (5%) als C-Quelle und KNO3 (1%) als N-Quelle, so kann durch Zusatz von Glucon- bzw. Citronensäure vor und nach dem Zeitpunkt des fast völligen Glucoseverbrauches eine Mehranhäufung von Oxalsäure erzielt werden. Die auf die Kultur und auf den Verbrauch an Citronensäure bezogene Ausbeute ist von der Temperatur und dem Zeitpunkt des Zusatzes abhängig. Bei 43° C wurde für die Zeit nach dem fast völligen Glucoseverbrauch ein Einbau von C14 aus Gluconsäure-C14 (U) und Citronensäure-1,5-C14 in die Oxalsäure nachgewiesen. Unter diesen Bedingungen können also beide Säuren als C-Quelle für die Oxalsäureanhäufung dienen. Es wird vermutet, daß die Mehranhäufung von Oxalsäure durchweg mit einem Umsatz von Glucon- und Citronensäure u. a. in Oxalsäure verknüpft ist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409158
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  • 15
    Electronic Resource
    Electronic Resource
    Oxalate accumulation from citrate by Aspergillus niger (1975)
    Springer
    Archives of microbiology 103 (1975), S. 185-189 
    Details
    ISSN: 1432-072X
    Keywords: Oxalate Accumulation ; Aspergillus ; Citrate Degradation ; Oxaloacetate Cleavage ; Glyoxylate Oxidation ; Enzyme Synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Carbon-14 was incorporated from citrate-1,5-14C, glyoxylate-14C(U), or glyoxylate-1-14C into oxalate by cultures of Aspergillus niger pregrown on a medium with glucose as the sole source of carbon. Glyoxylate-14C(U) was superior to glyoxylate-1-14C and citrate-1,5-14C as a source of incorporation. By addition of a great amount of citrate the accumulation of oxalate was accelerated and its maximum yield increased. In a cell-free extract from mycelium forming oxalate from citrate the enzyme oxaloacetate hydrolase (EC 3.7.1.1) was identified. Its in vitro activity per flask exceeded the rate of in vivo accumulation of oxalate. Glyoxylate oxidizing enzymes (glycolate oxidase, EC 1.1.3.1; glyoxylate oxidase, EC 1.2.3.5; NAD(P)-dependent glyoxylate dehydrogenase; glyoxylate dehydrogenase, CoA-oxalylating, EC 1.2.1.17) could not be detected in cell-free extracts. It is concluded that in cultures accumulating oxalate from citrate after pregrowth on glucose, oxalate arises by hydrolytic cleavage of oxaloacetate but not by oxidation of glyoxylate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00436348
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  • 16
    Electronic Resource
    Electronic Resource
    Gluconate accumulation and enzyme activities with extremely nitrogen-limited surface cultures of Aspergillus niger (1986)
    Springer
    Archives of microbiology 144 (1986), S. 151-157 
    Details
    ISSN: 1432-072X
    Keywords: Aspergillus niger ; Nitrogen limitation ; Gluconate accumulation ; Enzyme activities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Batch cultures of Aspergillus niger grown from conidia on a medium with high C/N ratio accumulated gluconate from glucose with a yield of 57%. During almost the whole time of accumulation there was no net synthesis of total protein in the mycelium but the activity per flask and the specific activity of glucose oxidase (EC 1.1.3.4) in mycelial extracts increased whereas both values decreased for glucose dehydrogenase (EC 1.1.99.10) ‘gluconate 6-phosphatase’ (cf. EC 3.1.3.1, 3.1.3.2), gluconokinase (EC 2.7.1.12), glucose 6-phosphate and phosphogluconate dehydrogenases (EC 1.1.1.49, EC 1.1.1.44), phosphoglucomutase (EC 2.7.5.1), and most enzymes of the Embden-Meyerhof pathway and the tricarboxylic acid cycle. Gluconate dehydratase (EC 4.2.1.39), gluconate dehydrogenase (EC 1.1.99.3) and enzymes of the Entner-Doudoroff pathway could not be detected. By cycloheximide the increase of glucose oxidase activity was inhibited. It is concluded that the high yield of gluconate was due mainly to the net (de novo) synthesis of glucose oxidase which occurred during protein turnover after the exhaustion of the nitrogen source, and which was not accompanied by a net synthesis of the other enzymes investigated. Some gluconate may also have been formed by hydrolytic cleavage of gluconate 6-phosphate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414726
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  • 17
    Electronic Resource
    Electronic Resource
    Introduction of plasmid pC194 into Bacillus thuringiensis by protoplast transformation and plasmid transfer (1984)
    Springer
    Archives of microbiology 139 (1984), S. 213-217 
    Details
    ISSN: 1432-072X
    Keywords: Bacillus thuringiensis ; Plasmid pC194 ; Transformation ; Plasmid transfer ; Protoplasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Staphylococcus aureus plasmid pC194 which codes for resistance to chloramphenicol was introduced into six Bacillus thuringiensis strains representing five varieties by protoplast transformation. Six other varieties could not be transformed. pC194 could be identified in transformed strains as autonomous plasmid. The transformed clones contained in addition a new extrachromosomal element of somewhat lower electrophoretic mobility hybridizing with pC194, and pC194 in multimeric forms. pC194 was also transferred from one B. thuringiensis variety to another and from Bacillus thuringiensis to Bacillus subtilis and vice versa by a conjugation-like process, requiring close cell-to-cell contact.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00402002
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  • 18
    Electronic Resource
    Electronic Resource
    Identification of the Bradyrhizobium japonicum degP gene as part of an operon containing small heat-shock protein genes (1998)
    Springer
    Archives of microbiology 169 (1998), S. 89-97 
    Details
    ISSN: 1432-072X
    Keywords: Key words Bradyrhizobium japonicum ; Heat shock ; DegP ; HtrA ; Periplasmic serine protease ; Small ; heat-shock protein ; Mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A degP (htrA)-like gene of Bradyrhizobium japonicum was identified immediately downstream of two genes (hspB and hspC) coding for small heat-shock proteins. All three genes are oriented in the same direction and are separated by only 85 and 72 bp, and a heat-inducible transcript covering hspB, hspC, and degP was detected by RT-PCR. These results show that the genes are organized in an operon. Two mutants, a degP insertion mutant and a ΔhspBCdegP mutant, were constructed by marker replacement mutagenesis. Immunoblot analysis performed with a serum raised against the amino-terminal end of IbpA, an HspB homolog of Escherichia coli, identified three heat-inducible protein bands in B. japonicum extract, one of which was missing in the deletion mutant. None of the mutants showed an obvious defect during growth at different temperatures, after heat-shock treatment, or in the presence of solvents. Moreover, they were not affected in root-nodule symbiosis, indicating that the small heat-shock proteins HspB and HspC and the DegP homolog of B. japonicum are not required under a wide range of growth conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002030050547
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  • 19
    Electronic Resource
    Electronic Resource
    Über den Einfluß hoher Temperatur auf die Oxalsäureanhäufung durch Aspergillus niger van Tiegh. (1960)
    Springer
    Archives of microbiology 36 (1960), S. 350-359 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Zusammenfassung Ein Stamm von Aspergillus niger häuft in einer physiologisch alkalischen Nährlösung bei 43° mehr Oxalsäure an als bei 30°. Dieser Unterschied beruht auf der verstärkten Anhäufung vor dem Zeitpunkt des völligen Glucoseverbrauches. Die autolytische Herkunft des größten Teils der nach diesem Zeitpunkt bei 30° und 43° noch hinzukommenden Oxalsäure wird nachgewiesen, ebenso die Intensivierung der Autolyse bei der hohen Temperatur. Dagegen, daß die Oxalsäure auch vor dem völligen Glucoseverbrauch autolytischen Ursprungs ist und bei 43° aus diesem Grunde in verstärktem Maße angehäuft wird, spricht der Befund, daß die Fraktion des NH4 +- und Amid-N vor diesem Zeitpunkt nur in sehr geringer Menge nachzuweisen ist. Es wird jedoch darauf hingewiesen, daß sie im Gegensatz zur Oxalsäure vielleicht wieder in das der Autolyse parallel laufende Wachstum mit einbezogen wird, solange noch Glucose vorhanden ist. Die Geschwindigkeit der Oxalsäurezersetzung ist bei 43° geringer als bei 30°. Eine Beteiligung dieses Temperatureffektes an der verstärkten Anhäufung bei 43° wird diskutiert, ebenso die Möglichkeit eines temperaturbedingten Shunt-Effektes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00418641
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  • 20
    Electronic Resource
    Electronic Resource
    Inhibition of Bradyrhizobium japonicum nifA-dependent nif gene activation by oxygen occurs at the NifA protein level and is irreversible (1989)
    Springer
    Archives of microbiology 151 (1989), S. 191-197 
    Details
    ISSN: 1432-072X
    Keywords: Bradyrhizobium japonicum ; NifA activity ; nifA mRNA half-lives ; Oxygen shift ; Post-transcriptional control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Previous work had shown that Bradyrhizobium japonicum nifA-dependent nif gene activation was inhibited by oxygen via a post-transcriptional mechanism. In the present report we demonstrate that this inhibition occurs at the NifA protein level and that it is irreversible. To narrow down the level of control the influence of oxygen on nifA mRNA stability and NifA protein activity was analyzed. The half-lives of B. japonicum and Klebsiella pneumoniae (control) nifA mRNAs derived from constitutively expressed nifA genes did not differ significantly under aerobic and anaerobic conditions which makes it unlikely that oxygen exerts its effect by selectively destabilizing B. japonicum nifA mRNA. By making use of its ability to activate in Escherichia coli a B. japonicum nifD' — 'lacZ fusion, the NifA protein was assayed by the determination of lacZ mRNA and β-galactosidase synthesis. Oxygen shift experiments clearly demonstrated that B. japonicum NifA activity (but not that of K. pneumoniae) was drastically reduced within minutes upon a shift to aerobiosis and that the inactivation was irreversible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00413129
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