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At least 1,315 records · Page 73Linked to original sources
PubMed1996

Intracellular endosymbiotic bacteria of Camponotus species (carpenter ants): systematics, evolution and ultrastructural characterization.

Intracellular endosymbiotic bacteria inherent to ants of the genus Camponotus were characterized. The bacteria were localized in bacteriocytes, which are specialized cells of both workers and queen ants; these cells are intercalated between epithelial cells of the midgut. The bacteriocytes show a different morphology from the normal epithelial cells and carry a large number of the rod-shaped Gram-negative bacteria free in the cytoplasm. The bacteria were never observed in the neighbouring epithelial cells, but they were found intracellularly in oocytes, strongly indicating a maternal transmission of the bacteria. The 16S DNA encoding rrs loci of the endosymbionts of four species of the genus Camponotus derived either from Germany (C. herculeanus and C. ligniperdus), North America (C. floridanus) or South America (C. rufipes) were cloned after polymerase chain reaction (PCR) amplification using oligonucleotides complementary to all so far known eubacterial rrs sequences. The DNA sequences of the rrs loci of the four endosymbionts were determined, and, using various genus- and species-specific oligonucleotides derived from variable regions in the rrs sequences, the identity of the bacteria present in the bacteriocytes and the ovarian cells was confirmed by PCR and in situ hybridization techniques. Comparison of the 16S DNA sequences with the available database showed the endosymbiotic bacteria to be members of the gamma-subclass of Proteobacteria. They formed a distinct taxonomic group, a sister taxon of the taxons defined by the tsetse fly and aphid endosymbionts. Within the gamma-subclass, the cluster of the ant, tsetse fly and aphid endosymbionts are placed adjacent to the family of Enterobacteriaceae. The evolutionary tree of the ant endosymbionts reflects the systematic classification and geographical distribution of their host insects, indicating an early co-evolution of the symbiotic partners and a vertical transmission of the bacteria.

Animals↗
PubMed2006

Iron-sulphur clusters and the problem with oxygen.

During the first billion years of life on the Earth, the environment was anaerobic. Iron and sulphur were plentiful, and they were recruited in the formation of iron-sulphur (Fe-S) clusters within ancient proteins. These clusters provided many enzymes with the ability to transfer electrons; to others they offered a cationic feature that tightly bound oxyanionic and nitrogenous metabolites. Still others acquired a crystallizing surface around which polypeptide could fold to establish a three-dimensional structure. However, the subsequent oxygenation of the Earth's atmosphere by photosynthetic organisms created a threat to cluster-dependent proteins that still has not been fully resolved. By oxidizing environmental iron, oxygen limits its bioavailability, requiring that organisms employ complex schemes with which to satisfy their iron requirement. More directly, oxygen species convert exposed Fe-S clusters to unstable forms that quickly decompose. Some microbes responded to this dilemma by retreating to anaerobic habitats. Others abandoned the use of low-potential electron-transfer pathways, which rely upon the least stable cluster enzymes, and developed antioxidant strategies to protect the remainder. These adjustments were only partially successful: largely because of their reliance upon Fe-S clusters, aerobes remain vulnerable to iron restriction and oxidative stress, features that higher organisms exploit in defending themselves against bacterial pathogens. Thus, the history of Fe-S clusters is an unusual one that has profoundly shaped contemporary microbial ecology.

Anaerobiosis↗
PubMed1987

Phenylalanine dehydrogenase of Bacillus badius. Purification, characterization and gene cloning.

Phenylalanine dehydrogenase produced by Bacillus badius IAM 11059 was purified from the crude extract of B. badius to homogeneity, as judged by disc gel electrophoresis. The enzyme has an isoelectric point of 3.5 and a relative molecular mass, Mr, of 310,000-360,000. The enzyme is composed of identical subunits with an Mr 41,000-42,000. The substrate specificity of the enzyme in the oxidative deamination reaction was high for L-phenylalanine, but rather low in the reductive amination reaction, with phenylpyruvate, p-hydroxyphenylpyruvate, and 2-oxohexanoate. The gene for the enzyme was cloned into Escherichia coli with plasmid pBR322 as a vector. The enzyme was expressed in high level in E. coli. The enzyme produced by E. coli transformant was purified to homogeneity and shown to be identical to that of B. badius IAM 11,059 with respect to the specific activity, Mr, subunit structure and amino acid composition.

Amino Acid Oxidoreductases↗
PubMed1996

Phylogenetic analysis of tnpR genes in mercury resistant soil bacteria: the relationship between DNA sequencing and RFLP typing approaches.

The diversity of resolvase (tnpR) genes carried by a number of mercury resistant soil bacteria has been investigated by DNA sequencing. The resulting DNA sequence information was compared to previously published tnpR DNA sequences and to previously published restriction fragment length polymorphism (RFLP) data, permitting the relationships between DNA sequencing and RFLP approaches to be studied by the use of phylogenetic trees. DNA maximum likelihood and DNA parsimony were used to construct a variety of phylogenetic trees. DNA sequencing confirmed the validity of RFLP analysis and highlighted the importance of restriction endonuclease choice upon the resulting RFLP patterns and dendrogram topology. The tnpR genes of two previously uncharacterised mercury resistant bacteria, T2-7 and T2-12 were also studied. DNA sequence data placed T2-7 in a previously described gene class, tnpR-D and T2-12 in a new gene class, tnpR-F. The significance of this data with respect to the recombination and evolution events occurring within bacterial populations are discussed.

Base Sequence↗
PubMed2000

The colanic acid gene cluster of Salmonella enterica has a complex history.

The colanic acid gene cluster of Salmonella enterica LT2 was sequenced and compared with that of Escherichia coli K-12. The two clusters are similar with divergence slightly higher than average for genes of the two species. The cluster was divided into four blocks by GC content and seems likely to have transferred from a higher GC content species to the ancestor of E. coli and S. enterica. All 19 genes of K-12 and 13 genes of LT2 appear to have undergone random genetic drift with amelioration of the GC content. However, in the case of S. enterica, we believe that the six genes of the GDP-fucose pathway group were replaced relatively recently by genes closely related to those of the original donor species. Two repetitive elements were observed: a bacterial interspersed mosaic element in the intergenic region between wzx and wcaK in K-12 only and a RSA (repetitive sequence element) sequence between wcaJ and wzx in LT2 only.

Bacterial Proteins↗
PubMed1979

Gene exchange and natural selection cause Bacillus subtilis to evolve in soil culture.

Strains of Bacillus subtilis exchange linked blocks of genes when growing together in soil; such exchange leads to extensive reorganization of the genotypic structure of the population and to the appearance and eventual dominance of a single phenotype. This process illustrates how recombination and selection lead to adaptive changes in populations.

Bacillus subtilis↗
PubMed2003

A genomic view of the human-Bacteroides thetaiotaomicron symbiosis.

The human gut is colonized with a vast community of indigenous microorganisms that help shape our biology. Here, we present the complete genome sequence of the Gram-negative anaerobe Bacteroides thetaiotaomicron, a dominant member of our normal distal intestinal microbiota. Its 4779-member proteome includes an elaborate apparatus for acquiring and hydrolyzing otherwise indigestible dietary polysaccharides and an associated environment-sensing system consisting of a large repertoire of extracytoplasmic function sigma factors and one- and two-component signal transduction systems. These and other expanded paralogous groups shed light on the molecular mechanisms underlying symbiotic host-bacterial relationships in our intestine.

Adult↗
PubMed1967

Life at high temperatures. Evolutionary, ecological, and biochemical significance of organisms living in hot springs is discussed.

The time is now ripe for a concerted attack on the evolutionary, ecological, and molecular aspects of life at high temperatures. Hot springs provide nearly ideal ecosystems for such study, since they are natural environments of great antiquity and relative constancy, where organisms have evolved to meet the environmental challenges of high temperatures. Even from our present limited knowledge, we can draw a number of conclusions.

Adaptation, Physiological↗
PubMed1992

Evidence that eukaryotes and eocyte prokaryotes are immediate relatives.

The phylogenetic origin of eukaryotes has been unclear because eukaryotic nuclear genes have diverged substantially from prokaryotic ones. The genes coding for elongation factor EF-1 alpha were compared among various organisms. The EF-1 alpha sequences of eukaryotes contained an 11-amino acid segment that was also found in eocytes (extremely thermophilic, sulfur-metabolizing bacteria) but that was absent in all other bacteria. The related (paralogous) genes encoding elongation factor EF-2 and initiation factor IF-2 also lacked the 11-amino acid insert. These data imply that the eocytes are the closest surviving relatives (sister taxon) of the eukaryotes.

Amino Acid Sequence↗
PubMed1989

Chromosomal location and evolutionary rate variation in enterobacterial genes.

The basal rate of DNA sequence evolution in enterobacteria, as seen in the extent of divergence between Escherichia coli and Salmonella typhimurium, varies greatly among genes, even when only "silent" sites are considered. The degree of divergence is clearly related to the level of gene expression, reflecting constraints on synonymous codon choice. However, where this constraint is weak, among genes not expressed at high levels, divergence is also related to the chromosomal location of the gene; it appears that genes furthest away from oriC, the origin of replication, have a mutation rate approximately two times that of genes near oriC.

Bias↗
PubMed1996

Life's last domain.

Explore the source record for details and available documents.

Biological Evolution↗
PubMed1998

Isolation of acidophilic methane-oxidizing bacteria from northern peat wetlands.

Acidic northern wetlands are an important source of methane, one of the gases that contributes to global warming. Methane oxidation in the surface of these acidic wetlands can reduce the methane flux to the atmosphere up to 90 percent. Here the isolation of three methanotrophic microorganisms from three boreal forest sites is reported. They are moderately acidophilic organisms and have a soluble methane monooxygenase. In contrast to the known groups of methanotrophs, 16S ribosomal DNA sequence analysis shows that they are affiliated with the acidophilic heterotrophic bacterium Beijerinckia indica subsp. indica.

Amino Acid Sequence↗
PubMed1979

DNA organization of Methanobacterium thermoautotrophicum.

The organism Methanobacterium thermoautotrophicum, an archaebacterium, is envolutionarily very distant from both traditional prokaryotes and eukaryotes. Its genome (DNA) has physical characteristics typical of most prokaryotes except that it is quite small (about 10(9) daltons, less than half the size of the genome of Escherichia coli) and contains a significant amount (6 percent) DNA which renatures extremely rapidly.

Base Sequence↗