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D Riesenberg

Publications and source records attributed to D Riesenberg.

47 records · Page 3Linked to original sources
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↗
PubMed1982

Positive involvement of ppGpp in derepression of the nif operon in Klebsiella pneumoniae.

The kinetics of derepression of the enzyme nitrogenase were investigated, after exhaustion of a limiting amount of ammonium from the culture medium, in a prototrophic stringent-relaxed pair of Klebsiella pneumoniae strains and in their F relA+-F relA derivatives. The results indicate that ppGpp (guanosine 3'-5' diphosphate) increases the nitrogen fixation capability of K. pneumoniae by at least three different mechanisms. (1) It prevents exhaustion of the ATP pool when nitrogen starvation is imposed. (2) The translational defects in relaxed mutants are suppressed by ppGpp during nif derepression. (3) The synthesis of nitrogenase components is at least five times higher in the presence of ppGpp than in its absence. This latter conclusion was based on experimental results obtained when following the incorporation of (35S)-methionine into nitrogenase components after pulse labelling at various time intervals during nif derepression. The nitrogenase components were separated by solid phase radioimmunoassay as well as by two-dimensional gel electrophoresis.

Adenine↗
PubMed1981

Isolation and characterization of prototrophic relaxed mutants of Klebsiella pneumoniae.

A new selection procedure has been developed for isolating prototrophic relaxed mutants of Klebsiella pneumoniae. Two mutants were isolated. One of them showed a fully relaxed phenotype, while the other one behaved in a semi-relaxed way. The wild-type strain, as well as the rel mutants exerted similar patterns to their E. coli counterparts in RNA, protein, ppGpp and pppGpp accumulation during amino starvation, carbon source shift-down and nitrogen starvation. Both mutants became stringent after introducing an F'-factor carrying the relA+ allele from Escherichia coli. The relaxed phenotype could be recovered by curing the F'-factor. Some of the pleiotropic consequences of rel mutations found in E. coli are present in the Klebsiella mutants also while some of them are absent. The mutants are defective in dinitrogen fixation after the exhaustion of limiting ammonium from the culture medium. However, their merodiploid derivatives, carrying the E. coli relA+ allele, showed the wild-type level of nitrogenase activity under the same conditions.

Carbon↗
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↗
PubMedDate not supplied

Diagnostic decision support systems.

Diagnostic decision support systems are ready for prime time. We used them in a general medical clinic and found that they could suggest new diagnostic possibilities, focus thinking about clinical problems, and serve as a tool for recertification preparation. In addition, we have found diagnostic decision support systems useful for the novice clinician (fourth-year medical students and interns). These tools serve as a reminder system for learners, suggesting questions to ask the patient, physical exam components to complete, and tests to order. The novice clinician may also use these systems in preparing case presentations. The systems reviewed vary in the ways we described earlier, and there is no one "best buy." Which program is right for you depends on how much detail you want, whether you prefer a CD or internet format, and in what setting you practice. Demos are available from most vendors: Try them out, make a choice, and get on with the business of enhanced diagnostic decision making.

Decision Support Systems, Clinical↗