Biomedical subjects

L Achenbach-Richter

Publications and source records attributed to L Achenbach-Richter.

4 recordsLinked to original sources

PubMed1988

The ribosomal gene spacer region in archaebacteria.

Sequences for the spacer regions that separate the 16S and 23S ribosomal RNA genes have been determined for four more (strategically placed) archaebacteria. These confirm the general rule that methanogens and extreme halophiles have spacers that contain a single tRNAala gene, while tRNA genes are not found in the spacer region of the true extreme thermophiles. The present study also shows that the spacer regions from the sulfate reducing Archaeglobus and the extreme thermophile Thermococcus (both of which cluster phylogenetically with the methanogens and extreme halophiles) contain each a tRNAala gene. Thus, not only all methanogens and extreme halophiles show this characteristic, but all organisms on the "methanogen branch" of the archaebacterial tree appear to do so. The finding of a tRNA gene in the spacer region of the extreme thermophile Thermococcus celer is the first known phenotypic property that links this organism with its phylogenetic counterparts, the methanogens, rather than with its phenotypic counterparts, the sulfur-dependent extreme thermophiles.

Alanine↗

PubMed1988

Rooting the archaebacterial tree: the pivotal role of Thermococcus celer in archaebacterial evolution.

The sequence of the 16S ribosomal RNA gene from the archaebacterium Thermococcus celer shows the organism to be related to the methanogenic archaebacteria rather than to its phenotypic counterparts, the extremely thermophilic archaebacteria. This conclusion turns on the position of the root of the archaebacterial phylogenetic tree, however. The problems encountered in rooting this tree are analyzed in detail. Under conditions that suppress evolutionary noise both the parsimony and evolutionary distance methods yield a root location (using a number of eubacterial or eukaryotic outgroup sequences) that is consistent with that determined by an "internal rooting" method, based upon an (approximate) determination of relative evolutionary rates.

Archaea↗

PubMed1987

A possible biochemical missing link among archaebacteria.

Until recently all archaebacteria isolated conformed to one of three basic phenotypes: they were either methanogens, extreme halophiles, or ('sulphur-dependent') extreme thermophiles. However, a novel phenotype, that fits none of these categories, has recently been described. The organism, strain VC-16 (tentatively called "Archaeoglobus fulgidus") reduces sulphate--the only archaebacterium so far known to do so--and makes very small quantities of methane, although it lacks some of the cofactors normally associated with methanogenesis. These characteristics suggest that strain VC-16 might represent a transition form between an anaerobic thermophilic sulfur-based type of metabolism (which seems to be the ancestral metabolism for archaebacteria and methanogenesis (which somehow then derives from it). We here show that the lineage represented by strain VC-16 arises from the archaebacterial tree precisely where such an interpretation would predict that it would, between the Methanococcus lineage (which is the deepest of the methanogen branchings) and that of Thermococcus (the deepest of all branchings on the methanogen side of the tree).

Archaea↗

PubMed1987

Were the original eubacteria thermophiles?

Thermotoga maritima is one of the more unusual eubacteria: It is highly thermophilic, growing at temperatures higher than any other eubacterium; its cell wall appears to have a unique structure and its lipids a unique composition; and the organism is surrounded by a loose-fitting sheath of unknown function. Its phenotypic uniqueness is matched by its phylogenetic position; Thermotoga maritima represents the deepest known branching in the eubacterial line of descent, as measured by ribosomal RNA sequence comparisons. T. maritima also represents the most slowly evolving of eubacterial lineages. The fact that the two deepest branchings in the eubacterial line of descent (the other, the green non-sulfur bacteria and relatives, i.e. Chloroflexus, Thermomicrobium, etc.) are both basically thermophilic and slowly evolving, strongly suggests that all eubacteria have ultimately arisen from a thermophilic ancestor.

Bacteria↗