Zentralblatt für Bakteriologie Mikrobiologie und Hygiene: I. Abt. Originale C: Allgemeine, angewandte und ?kologische Mikrobiologie最新文献

Methanobrevibacter arboriphilus DNA was isolated after treatment of the cells with bacitracin in a sucrose containing growth medium. Hind III restriction fragments of the DNA were inserted into an expression vector plasmid. The newly constructed plasmids when introduced into E. coli gave rise to the synthesis of polypeptides coded for by the methanogen DNA. The expression of genetic information from the Methanobrevibacter DNA in E. coli is efficient as judged by the total molecular weight of the polypeptides found as compared to the length of the Methanobrevibacter DNA carried on the plasmids.

Archaebacteria are a group of organisms distinct from all others at the highest level. They are no more related to other bacteria, i.e., the true bacteria (eubacteria) than they are to eucaryotic cells. Archaebacteria, eubacteria and (some aspect of) the eucaryotic cell each represent separate primary lines of descent.

The archaebacteria comprise a small but diverse collection of phenotypes. While they have certain unique common phenotypic characteristics, it would have been difficult to group them convincingly on the basis of these. What was needed (and what is needed in all reliable and convincing phylogenetic measurement) is a genotypic neutral measure of genealogical relationships. Macromolecules are chronometric, in that other things being constant, changes in their sequences mark time (in a stochastic, not a metronomic way). Comparative sequence analysis is therefore a powerful measure of genealogical relationships. Using such (neutral) genotypic measures, phylogenetic ordering at the higher levels can be reliably determined — and archaebacteria can be recognized for the primary kingdom that they are.

Although it is too early to generalize with certainty, it seems that the archaebacteria differ from the other two major groups in significant details of most, if not all, molecular processes. [This is the same way in which “procaryotes” were known to differ from eucaryotes at the mloecular level.] It does not seem reasonable intuitively that this extent of difference among the three primary kingdoms can be accounted for by one of the phenotypes undergoing an extensive evolution to become the others. Rather, it seems that all lines have shared a common ancestor that possessed a more rudimentary, less detailed, phenotype, and so each has evolved separately the details in which they differ. The universal common ancestor should be called a progenote; it is an organism still in the throes of evolving the link between genotype and phenotype. The important question is why there is a universal, unique ancestor.

The existence of archaebacteria provides a new and powerful perspective on the origin of the eucaryotic cell. As a result, our concept of eucaryotic origins will undergo revision. The conventional endosymbiotic model for eucaryotic origins is no longer a sufficient explanation. The main characteristics of the eucaryotic cell — those that distinguish it at the molecular level — were evolved long before the endosymbioses that led to he mitochon- drion and the chloroplast. The nature of the eucaryotic cell is perhaps related to the nature of the ancestral progenote.

The evolutionary questions and answers offered by archaebacteria should go far to rekindle the biologist's flagging interest in evolutionary matters, and hopefully divert biology to some extent from its present course of technological adventurism.

To resolve difficulties in tracing the early phylogenies of halobacteria and other archaebacteria, a model involving gene transfer is proposed

A newly isolated methanogenic archaebacterium, Methanothrix soehngenii (“acetate organism”) was characterized by oligonucleotide cataloguing of its 16S ribosomal RNA, using an improved method for sequenzing ribonuclease T₁ resistant oligonucleotides. M. soehngenii was found to be a member of the order Methanomicrobiales and is specifically related to Methanosarcina barkeri, but not closely so.

The DNA of 5 species of eubacteria and 5 species of archaebacteria was isolated by isopyknic centrifugation in metrizamide density gradients. It is associated with high amounts (protein: DNA ≈ 0.25 w/w) of small, acid-soluble proteins with molecular weights ranging from 5,500 to 14,300. Electrophoreses of these proteins according to charge density showed that nearly all of them are very basic, some of the archaebacterial proteins even as basic as calf thymus histones.

Antibodies against the histone-like protein of Escherichia coli formed precipitates with extracts of 13 species of eubacteria, of which some were phylogenetically quite distant from Escherichia coli, but not with extracts from archaebacteria. Dodecylsulfate Polyacrylamide gel electrophoresis of the precipitates yielded bands of identical molecular weights as those obtained after metrizamide centrifugation. No precipitation could be detected with extracts from archaebacteria or with calf thymus histones.

Antibodies against the histone-like protein of Thermoplasma reacted only with the corresponding extract, but not with those from other archaebacteria e. g. Sulfolobus, Thermoproteus, Methanobacterium, Methanococcus and Methanosarcina. They also did not yield precipitates with extracts of eubacteria and with calf thymus histones.

A phylogenetic tree analysis of small ribosomal subunit RNA (S-rRNA) gene sequences from Aspergillus nidulans, yeast, human and mouse mitochondria, E. coli, maize chloroplasts and nuclei from yeast and animals supports the endosymbiotic eubacterial origin of mitochondria and further raises the possibility, that fungal and animal mitochondria derive from different bacterial species.

Two archaebacterial 5 S rRNA sequences (from Halobacterium cutirubrum and Thermoplasma acidophilum) were incorporated into a recently described 5S tree: the two sequences exhibit a common root and diverge early from the nuclear branch.

The present sequence data are compatible with the idea that unicellular precursors to the eukaroytic kingdoms have been formed by divergence of archaebacteria-like cells prior to the invasion of endosymbiotic eubacteria.

Cell-free extracts were prepared from seven extremely halophilic, six methanogenic and five thermoacidophilic archaebacteria covering nearly all known subgroups. The 150,000 X g supernatants were incubated with diphtheria toxin (DT) and NAD [adenine-¹⁴C]. TCA-precipitable radioactivity was compared with that from toxin-free controls. All eighteen archaebacterial strains gave significant, DT-dependent protein labelling, as had done all eukaryotic extracts previously assayed. No eubacterial nor mitochondrial proteins were substrates for DT. Therefore the DT reaction in this simple form provides a general method for identifying a procaryote as an archaebacterium.

SDS-gel electrophoresis of the reaction products followed by autoradiography revealed in many but not all cases one predominant labelled protein band; nearly all halophilic gels and several methanogenic ones showed minor bands.

Direct evidence from H. cutirubrum (Kessel and Klink, 1980) and the known specifity of DT for eukaryotic EF-2 led to the conclusion that only the analogous archaebacterial EF was ADP-ribosylated, minor bands being products of proteolysis. The apparent molecular weights showed a considerable diversity and formed three groups: The thermoacidophilic elongation factors banded between M_r 74,000 and M_r 83,000, the methanogenic ones from M_r 83,000 up to M_r 89,000, the halophilic ones between M_r 101,000 and M_r 111,000. With the same technique eukaryotic factors gave values of Mr 96,000.

The cell wall glycoprotein of Halobacteria contains sulphate covalenty bound to different types of saccharides. A high molecular weight saccharide (HMW-saccharide), which is N-glycosidically linked to Asn was found to have the following composition: 1 gal: 1 galN: 1 glcN: 2 galUA: 2 SO₄^2-. This HMW-saccharide is not a heterosaccharide, but exhibits rather a repeating unit structure similar to that of the animal glycosaminoglycans. Incorporation into the cell wall glycoprotein of this HMW-saccharide is specifically inhibited by the antibiotic bacitracin (Wieland et al., 1980). This inhibition results in a remarkable change of the halobacterial shape: the normally rod shaped cells grown in the presence of bacitracin convert to regular spheres (Mescher and Strominger, 1975).

This HMW-saccharide is synthesized bound to a lipid anchor: only after completion the fully sulphated saccharide is transferred to the core protein.