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

The autotrophic methanogenic bacterium Methanobacterium thermoautotrophicum assimilates CO₂ via a novel CO₂ fixation pathway rather than via the Reductive Pentosephosphate Cycle (Calvin Cycle). The first known fixation product of this pathway is acetyl CoA which is the starting compound for the synthesis of the carbon skeleton of all cell compounds except for one-carbon units. This central intermediate appears to be synthesized from 2 CO₂ via bound one-carbon units rather than via cleavage of a compound which itself is synthesized from acetyl CoA and CO₂. Further CO₂ fixation proceeds via the reductive carboxylation of acetyl CoA to pyruvate, the carboxylation of phosphoenolpyruvate to oxaloacetate, and the reductive carboxylation of succinyl CoA to α-ketoglutarate. Triosephosphate and hexosephosphate synthesis proceeds from acetyl CoA and CO₂ via pyruvate and phosphoenolpyruvate.

This contribution describes the outlines of the proposed new pathway and summarizes the experimental evidence on which it is based.

The acidothermophilic Archaebacteria, Sulfolobus acidocaldarius and S. brierleyi, oxidized elemental sulfur anaerobically producing sulfuric acid by using Mo (VI) as an apparent electron acceptor. Molybdenum reduction resulted in the formation of a blue color which was intensified in the presence of aluminum at concentrations of 20–50 mM. Molybdenum was not reduced when S. brierleyi was grown anaerobically on yeast extract as an energy source, suggesting that the organic substrate was utilized in a fermentative metabolism mode.

Halobacterium pharaonis sp. nov. was isolated from the alkaline brines of eutrophic desert lakes of Wadi Natrun, Egypt. The new species differs from the Halobacterium species so far described in being alkaliphilic, in its extremely low Mg²⁺ requirement for growth, and in its DNA base composition (64.3 mol% guanine + cytosine, determined by thermal decomposition; no satellite DNA). Magnesium in concentrations above 0.01 mol/1 (≈ 0.25% w/v MgSO₄·7H²O) inhibits growth. Good growth occurs between pH 7.7 and 9.3, optimal growth at pH 8.5.

Methanogenic bacteria have catalyzed a revolution in our understanding of procaryote diversity. The development of a comprehensive phylogenetic basis for viewing methanogen relationships has modified considerably our concept of both the phylogenetic and phenotypic complexity of the bacteria. It provided the basis for description of a new taxonomic scheme for the methanogenic bacteria in which a measure of phylogenetic relationships served as a framework for organizing an extensive range of syntactic features circumscribing the group. The scheme illustrates in a general way the central role that relationships can play in bacterial systematics.

This article reviews available data on geochemical fossils and their potential precursors in archaebacteria. The evidence compiled during the last 3 years suggests that a large fraction of the isoprenoid hydrocarbons in sedimentary rocks as old as Precambrian is of archaebacterial origin and that archaebacteria have contributed significantly to the sedimentary organic matter through most of earth's history, at least from the late Proterozoic on. It remains to be seen whether geochemical fossils of archaebacterial origin have survived from Archean times.

The nucleotide sequence of Thermoplasma acidophilum tRNA{ie} has been shown to be: pGCCGGGGs⁴UGGCUCANCUGGAGGAGCm₂²GCCGGAC_m UCAUt⁶AAUCCGGAG-GUCUCGGGψψC_mGAUCCCCGAUCCCGGCACCA_oH. The tRNA contains eight modified nucleosides including the sequence ψψC_m (54–56) which has been proposed as a unique feature of archaebacterial tRNAs. One modification is unknown but it is likely to be typically archaebacterial (N-15). Of the remaining four, one (s⁴U-8) is a typical eubac-terial modification and one (m₂²G-26) is a typical eukaryotic modification. The sequence shows little homology with any other published tRNA but shows almost 90% homology with the ancestral quasi-species sequence deduced by Eigen and Winter-Oswatitsch (1981).

The requirement for the small ribosomal 5S RNA as an integral part of the protein synthesizing machinery, the ribosome, has been conserved throughout the course of evolution. Eubacterial, eukaryotic, archaebacterial and chloroplast 5S RNAs have been used for protein binding studies, reconstitution experiments and structural analysis with the single strand specific ribonuclease S₁ These comparative studies reflect the phylogenetic relationship of the individual species examined; besides the two major classes, eubacterial and eukaryotic 5 S RNA, archaebacterial 5S RNA represents a further class, which is structurally and functionally distinct.

Chloroplast 5S RNA is demonstrated to be closely related to the eubacterial class.

Molecular cloning and Southern hybridization techniques have allowed us to show that the genome of Halobacterium halobium contains a large number of repeated sequences, comprising many families. Some elements from different families may be clustered in the genome. Rearrangements (transpositions?) affecting such elements occur frequently and spontaneously. Some H. halobium repeat sequence families are also represented in the genome of H. volcanii.

The genomic DNA of Halobacterium halobium and several other extremely halophilic species is separated on bisacrylamide/malachitegreen columns into two fractions which differ considerably in their GC content. It is shown that the AT richer fraction exhibits a high degree of variability and often forms circular DNA elements of various sizes. The major circular DNA behaves like a plasmid in that it is present in a constant number of copies. Insertions of IS-like elements of different lengths seem to be responsible for the genetic variability. These insertions are reversible in some instances. This has allowed us to localize the genetic determinant for gas vesicle formation on the major circular DNA.

By comparing the nucleotide alignment of 5S rRNA sequences, we have constructed a phylogenic tree of 95 species of organisms, including a unique group of bacteria for which we previously proposed the name “metabacteria”. Various lines of evidence indicate that the metabacteria are more related to eukaryotes than to eubacteria.