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F Bergter

Publications and source records attributed to F Bergter.

At least 19 recordsLinked to original sources
PubMed1987

Dynamic model of the pathogenesis of Mengo virus infection in mice.

A mathematical model of the pathogenesis of experimental Mengo virus infection in mice has been developed and fitted using kinetic data of both virus multiplication in different organs and mortality. The behaviour of the model proved to be bistable. In contrast to the widely accepted hypothesis that an acutely virus-infected host dies when virus replication has attained a critical level in the main target organ, the present results showed the following: the maximum virus titre in brain, the main target organ, has been reached already 24 hr post infection (p.i.) but the animals began to die since 60 hr. Hence, it was postulated and confirmed by a good model fit to the experimental data that the so-called AUC (area under the curve) of the virus multiplication kinetics may be a critical quantity. From this finding a hypothesis was deduced assuming that in the presence of high amounts of the virus the antiviral effect of IFN wanes with time. Since this process accounts for death, it may be a potential target of antiviral therapy.

Animals↗
PubMed1984

Mixed culture kinetics of stringent and relaxed Escherichia coli cells in glucose-limited chemostat.

The mixed culture kinetics of stringent and relaxed Escherichia coli cells were investigated in a glucose-limited chemostat at different dilution rates. Independent of the dilution rate the stringent cells competed out the relaxed cells. But the number of generations necessary for displaying the relaxed cells by the stringent ones increased with increasing dilution rate. The results are discussed as a consequence of the regulatory role of guanosine-5'-diphosphate-3'-diphosphate (ppGpp) which is known to be present at different concentrations in stringent and relaxed cells under conditions of nutrient limitation. In addition, it is postulated that the coefficient of the maintenance metabolism according to PIRT (1965) is slower in stringent cells than in relaxed cells of E. coli.

Cell Division↗
PubMed1984

Establishment of a system suitable for analysis of balanced and unbalanced growth of Streptomyces hygroscopicus.

A small-scale system was developed in which balanced growth of Streptomyces hygroscopicus occurred. Although the balanced growth, verified by corresponding increase of ATP, DNA, RNA, protein and mycelial length, was restricted to a relatively short period of the life cycle, it lasted for at least two doublings. The conditions for balanced growth could be altered by various treatments to induce imbalance. This system could be applied to study regulation in the mycelium under well-defined conditions.

Adenosine Triphosphate↗
PubMed1984

Effect of serine hydroxamate and methyl alpha-D-glucopyranoside treatment on nucleoside polyphosphate pools, RNA and protein accumulation in Streptomyces hygroscopicus.

The accumulation of RNA and protein and the kinetics of nucleoside triphosphate and guanosine polyphosphate pools during amino acid starvation and carbon source downshift were investigated in Streptomyces hygroscopicus. RNA accumulation was controlled stringently during both amino acid starvation and carbon source downshift. The pool size of ppGpp increased dramatically under these conditions. However, the intracellular concentrations of nucleoside triphosphates were low and the concentration of guanosine polyphosphates was much lower than in Escherichia coli. The possible significance of this phenomenon in the regulation is discussed.

Adenosine Triphosphate↗
PubMed1979

Dependence of macromolecular composition and morphology of Streptomyces hygroscopicus on specific growth rate.

The dependence of macromolecular composition and morphology of Streptomyces hygroscopicus on specific growth rate micron was investigated. The percentage of DNA on dry weight (%DNA) is constant, % protein is also nearly independent of micron whereas %RNA rises considerably with increasing micron, regarding mycelia grown in glucose-limited and ammonium-limited continuous cultures as well as in discontinuous cultures with various carbon sources. It is probable that the overall synthesis of DNA, RNA and protein is regulated in the mycelium-forming bacterium S. hygroscopicus by the same mechanisms found in unicellular bacteria like Escherichia coli because of the qualitatively similar dependence of %DNA, %RNA and %protein on micron. But differences exist in quantitative regard whereby %DNA, %RNA and %protein of S. hygroscopicus are much smaller at low micron and, with increasing micron, approach those of unicellular bacteria. The hypothesis about the increase of the hyphal regions showing high synthesis activity in S. hygroscopicus mycelia grown in glucose-limited continuous cultures with increasing micron -- derived from comparison of macromolecular composition of S. hygroscopicus and unicellular bacteria -- was confirmed autoradiographically with respect to protein synthesis. The increase of the part of mycelial regions showing high cytoplasmic activity results in an increase of mean hyphal diameter, of mean relative apical growth rate alpha and/or mean relative branching rate beta. Beta depends sigmoidally and alpha inverses sigmoidally on micron. Therefore, the morphology of the mycelium determined by alpha and beta also depends on micron. The hyphal growth unit L/N, the distance from apex to first branch Lp and the mean distance between neighbouring branches Ln decline with increasing micron and reach a minimum at micron = 0.32 (1/h). A further rise of micron is accompanied with an increase of L/N, Lp and Ln. This means that mycelia growing slowly or very quickly have a loose form whereas quickly growing mycelia are characterized by a more compact form. The complicated dependence of alpha, beta, L/N, Lp and Ln on micron indicates that the morphology is regulated by different mechanisms depending on the specific growth rate.

Ammonium Chloride↗
PubMed1979

Distribution functions of variables characterizing the mycelial morphology of Streptomyces hygroscopicus grown in glucose-limited chemostat cultures.

The distribution of variables characterizing the morphology of the mycelium of Streptomyces hygroscopicus grown in glucose-limited chemostat cultures at different specific growth rates were investigated statistically. The values of the hyphal growth unit (L/N) and the values of the distance from the apex to the first branch (Lp) are normally distributed, but the values of the distance between neighbouring branches are logarithmically normal distributed. The distribution functions are discussed from the biological point of view.

Glucose↗
PubMed1978

[Maintenance metabolism in glucose-limited chemostat cultures of Streptomyces hygroscopicus].

Investigations with the mycelium forming bacterium Streptomyces hygroscopicus IMET JA 6599 in glucose-limited chemostat cultures gave a maintenance coefficient of m = 0.031 h-1. This low maintenance coefficient corresponds to those of moulds (RIGHELATO et al. 1968, CARTER et al. 1971). With a simple model structured in active and inactive biomass (x1 and x2) it was tried to explain the low maintenance coefficient of S. hygroscopicus in relation to nonfilamentous growing microorganisms. The model contains the transition rate k, which describes the transition of active biomass in inactive one and the decay rate beta, which considers the decay of hyphae. The model was used to study the influence of beta on the maintenance coefficient and it was shown that maintenance metabolism can be simulated by the parameter beta alone.

Glucose↗
PubMed1978

[Multiphasic growth of microorganisms: modeling and computer simulation of linear growth phases].

A phenomenological and a more causal model are developed for the multiphasic discontinuous growth. The first model distinguished between the lag-phase, the exponential phase, the transient phase from the exponential to the linear phase, the linear phase, the transient phase from the linear to the stationary phase, and the stationary phase. The parameters are rate constants, critical values of biomass, and time constants. The parameters are estimated for experimental data of growth of Candida lipolytica under limitation of thiamine (Müller et al. 1978). These data are fitted also by a more causal model. This second model is in agreement with Monod's idea that a linear growth phase may be due to an enzyme or enzyme system which has a constant activity. In the analysed case of limitation of thiamine the constancy of the dehydrogenase activity is caused by a constant level of the coenzymethiaminepyrophosphate. Thus, when such a thiamine requiring enzymatic step becomes to the "bottle-neck", bacterial culture switches over from exponential to linear growth. The end of linear phase is discussed more hypothetically by the high cooperativity of activity of dehydrogenases and the existence of a mimimal specific growth rate. The results of modeling and parameter estimation are compared with experimental data of C. lipolytica. These two models are able to interpret the growth kinetic of these multiphasic growth.

Candida↗
PubMed1978

[Growth kinetics of thiamine requiring Candida lipolytica during thiamine limitation: the existence of a linear growth phase].

The growth kinetics of batch cultures of the thiamine requiring Candida lipolytica 695 was investigated. It was established that a phase of logarithmic growth is followed by a linear growth phase. The time length of the linear phase and the relative increasing of the biomass during the linear phase are nearly constant and independend of the concentration of thiamine. The existence of the linear phase is discussed in connection with a constant activity of one of the two 2-ketoacid dehydrogenases as a bottle neck enzyme which needs thiamine pyrophosphate as coenzyme. Critical intracellular thiamine concentrations were calculated necessary for transition from the logarithmic to the linear phase and from the logarithmic to the stationary growth phase. Without the existence of the second critical thiamine concentration the linear growth would continue infinitely.

Candida↗
PubMed1977

[Bistability of pyruvate production by E. coli ML30 in continuous culture].

The pyruvate production of E. coli ML30 in continuous cultures was investigated. In a glucose mineralsalt medium with ammonium as the limiting substrate two stable stationary states (bistability) of pyruvate concentration were obtained. The bistability was limited to dilution rates lower than 0.3 h-1 and connected with a decrease of the yield coefficient (Y Glc) from approximately 0.45 to approximately 0.1.

Culture Media↗
PubMed1977

[Dependence of the specific growth rate of Escherichia coli MI 30 on the ammonia concentration].

The transient behaviour of ammonium limited continuous cultures of E. coli ML 30 led to the hypothesis that the bistability of pyruvate formation primarily is caused by a bistability of the ammonia metabolism. Therefore, a function of mu([NH+4]) should be expected different from that of Monod type. Measurements of the specific growth rate during washout of continuous cultures at different ammonium concentrations and at such low cell concentrations that the changes in the ammonium concentration of the medium could be neglected, showed a complex function with a relative minimum near 2 mg/1NH+4. This function allows bistability of the ammonium concentration in an ammonium limited continuous culture. The results are discussed on the basis of the two systems of ammonia assimilation found in prokaryotic cells.

Ammonia↗
PubMed1977

[Bistability in the activity of glutamine synthetase in ammonium-limiting chemostat cultures of Escherichia coli ML 30].

The approximative estimation of the function micron([NH+4]) in cultures of E. coli ML 30 had shown that bistability of the ammonium concentration in ammonium limited continuous cultures could be possible (BERGTER et al. 1977). This phenomenon suggested a bistability in the regulation of ammonia assimilation. Therefore, the activity of one key enzyme of the two ammonia assimilation systems was measured. The distribution of the activity of glutamine synthetase in ammonia limited continuous cultures after different transition states confirmed this suggestion.

Ammonia↗
PubMed1977

[Transient behavior of the ammonium-limited chemostatic cultures of Escherichia coli ML 30].

In connection with the bistability of pyruvate formation in ammonium limited continuous cultures of E. coli ML 30 (Bergter u. Roth 1977) the transient behaviour of cell density and pyruvate concentration were studied. Immediately after a shift up in the dilution rate from D = 0.15 h-1 to D = 0.6 h-1 the bacteria excreted pyruvate into the medium, followed by a resumption of pyruvate. The specific pyruvate formation rate as well as the specific growth rate reached the new steady state with damped oscillations. Possibly the excretion of pyruvate after the shift is caused by the higher non limiting concentrations of ammonium during the first of the transition. This hypothesis is supported by the transient behaviour of an ammonium limited continuous culture after a pulse of ammonium to the culture. The relations between ammonium metabolism and pyruvate formation are discussed.

Escherichia coli↗