Interspezifische Variabilität bei hypotrichen Ciliaten1

Interspecific variability in hypotrichous ciliates The genome organization of hypotrichous ciliates differs fundamentally from those of most other eukaryotic organisms. Every cell has two kinds of nuclei as is characteristic for ciliatese small generative micronuclei (Mi) whose DNA has a high molecular weight and which is organized in chromosomes, and vegetative macronuclei (Ma) which are very rich in DNA. The macronuclear DNA consists of so-called “gene-sized” DNA pieces, an organization which is not found in any other organism. This extraordinary genome organization offers a convenient experimental approach for studying evolutionary divergence at different molecular levels: 1. whole genomes, 2. subfractions of genomes, and 3. enzyme proteins. The comparison of unfractionated genomic DNA of hypotrichous ciliates by Dna-DNA hybridizations has yielded an unsuspected result: species that are closely related according to their morphology show an unusually low amount of sequence homology. The underlying reason might be that hypotrichous species separated early in eukaryotic evolution. Whereas the morphology of “closely related” species has changed only little, molecular evolution has led to major genomic changes that reflect the great evolutionary age of the species. The separation of native macronuclear DNA by gel electrophoresis produces species-specific DNA banding patterns based on different copy numbers of individual “gene-sized” DNA pieces in different species. These banding patterns allow the discrimination of sibling species which are morphologically very similar or even undistinguishable. Higher taxa can also be identified by means of DNA banding patterns. Cloned α- and β-tubulin genes were used in hybridization experiments to study the evolutionary divergence of individual DNA sequences in different hypotrichous species. The unusual Magenome organization makes such an analysis especially convenient. Characteristics of individual genes such as length number of sequence variants, copy number, and pattern of restriction sites can be compared with this method. The digestion of Mi-DNA with restriction endonucleases reveals differences in the repetitive DNA fraction of those genomes. Specific differences can be detected between closely related species and even between different populations of one species. The comparison of evolutionary divergence at the DNA level was supplemented by a comparison at the protein level. Enzyme electrophoresis proved to be a suitable method for the identification of otherwise indistinguishable species. Genetic ivergency (D-values) was estimated on the basis of allozyme data and a dendrogram was constructed reflecting the amount of genetic similarity between the species investigated. The discussion considers advantages and disadvantages of molecular characteristics for attacking taxonomic, phylogenetic, and evolutionary problems.     

Seasonal Development and Morphological Variability of Cyclotella ocellata (Bacillariophyceae) in the Eutrophic Lake Dagow (Germany)

The development of Cyclotella ocellata Pantocsek was studied systematically in the eutrophic, dimictic hardwater Lake Dagow from March to October, 1994. Cyclotella ocellata was the most important centric diatom in the lake with a maximum cell density of 6 × 10⁶ cells 1⁻¹. The seasonal development, characterized by a spring and a summer maximum, is considered in relation to environmental factors and the succession of the phytoplankton community. The amount of Cyclotella ocellata biomass as a proportion of the total phytoplankton biomass varied from 0.5 to 35%. In addition, seasonal changes in cell size and feature associated with sexual reproduction of Cyclotella ocellata were documented. Light and electron microscopic investigations demonstrate an extremely wide range of morphological variability of this natural population.     

New anthracycline antibiotics produced by interspecific recombinants of streptomycetes. IV. Antimicrobial activity of iremycin

The in vitro antimicrobial activity of iremycin (10-(alpha-L-rhodosaminyl)-gamma-rhodomycinone) was determined in comparison to that of doxorubicin, a 14-hydroxy-derivative of daunorubicin, which exhibited a strong antitumor activity and is useful in chemotherapy of human tumors. The MIC values determined by means of a standardized agar diffusion plate test indicated a lower antimicrobial activity of iremycin in vitro in comparison to that of doxorubicin. In contrast to doxorubicin, iremycin was highly active against Mycobacterium smegmatis, but five-fold less active than doxorubicin against Staphylococcus aureus, seven-fold less active against Bacillus subtilis, and twenty five-fold less active against Commamonas terrigena. Furthermore, iremycin was hundred-fold less active against a highly sensitive permeation mutant of Pseudomonas aeruginosa. No inducing activity on prophages in lysogenic E. coli cells was demonstrable for iremycin and no growth inhibition in the repair test was observable. In contrast, iremycin inhibited the multiplication of gamma-phages in the BIP test, but the MIC values of violamycin BI, doxorubicin and iremycin in this test system indicated that iremycin is two hundred fifty-fold less active than violamycin BI and ten-fold less active than doxorubicin. No serum binding was demonstrable for iremycin.     

A possible mechanism by which SV40 T-antigen stimulates rRNA synthesis

Binding of SV40 T-antigen to RNA polymerase I could account for the observation that T-antigen stimulates rRNA synthesis and that nucleoli do not stain for T-antigen. Two tests were performed to detect binding: a) RNA polymerase I was isolated and assayed in the presence of T-antigen; polymerase activity was enhanced. b) RNA polymerase I and T-antigen were mixed and then T-antigen complement fixation assays performed, complement fixation was not inhibited.     

Involvement of spectrin in the maintenance of phase-state asymmetry in the erythrocyte membrane

The fluorescent probe merocyanine 540 does not stain the plasma membrane of normal human or murine erythrocytes, nor of genetically abnormal human spherocytic erythrocytes. It does, however, stain erythrocyte membranes in several systems in which the underlying spectrin network is altered or missing. Because of the greater affinity of merocyanine 540 for fluid—phase lipid bilayers, these results suggest that the external leaflet of erythrocyte membranes becomes more disordered upon alteration or loss of the internal spectrin network. Analysis of the transbilayer arrangement of membrane phospholipids by digestion with phospholipase A2 suggests that lipid compositional asymmetry of the erythrocyte membrane is responsible for a phase-state asymmetry between the two lipid leaflets, and that spectrin is required to maintain this asymmetry and the gel-like state of the external leaflet.