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At least 1,387 records · Page 77Linked to original sources
PubMed1973

BCG vaccination of children against leprosy: seven-year findings of the controlled WHO trial in Burma.

A controlled study of the efficacy of BCG vaccination for the prevention of leprosy began in Burma at the end of August 1964. This paper presents the findings after 7 years-i.e., the results of 6 annual follow-up examinations up to the end of June 1971. The incidence rate in BCG-vaccinated children 0-4 years of age at intake was lower than that in children in the control group. The protection conferred by BCG was relatively low (44%) and applied only to early cases of leprosy, the great majority tuberculoid cases. BCG vaccination did not protect household contacts or children 5-14 years of age who were not exposed in the household. This reduction must be interpreted in the light of several factors: form of leprosy, bacterial status, lepromin reactivity, evolution of cases, and level of endemicity. Consequently it does not seem probable that the reduction in incidence would substantially affect the pattern or trend of the disease in an area similar to that where the study is being carried out; the probability would be much lower if not nil in regions of relatively low endemicity (1-2 per 1 000 or less).

Adolescent↗
PubMed1984

[Induction of repetitive nucleotide sequences. The probable mechanisms of genome evolution and gene conversion].

In the preselected site of pBR322 plasmid DNA related to the Tcr gene mutations were induced by the complementary single-stranded DNA restricts carrying alkylating groups. The alterations of the DNA primary structure in the mutagenized site were studied. It was found and that in the majority of mutants with the impaired Tcr gene function, the tandem direct repeats appeared. The repeats of 7-8 base pairs were localized in a fixed site of the Tcr gene, downstream of the palindrome. It is suggested that tandem repeats appear as a result of D-loops formation when single-stranded DNA forms a hairpin structure, due to the presence of palindromes. In the light of this notion, the tentative schemes of gene conversion and genome evolution are discussed.

Base Sequence↗
PubMed2000

Intraspecies variation in bacterial genomes: the need for a species genome concept.

Bacterial populations are clonal. Their evolution involves not only divergence between orthologous genes but also gain of genes from other clones or species, which has only recently been widely appreciated through macrorestriction mapping, genomic subtraction and complete genome sequencing. Genes can also be lost in response to selection or by random mutation after becoming redundant. The bacterial genome is a dynamic structure and intraspecies variation needs to be included in genome analysis if we are to gain insight into the full species genome.

Bacteria↗
PubMed1999

Endosymbiosis and evolution of the plant cell.

The bacterial origins of plastid division and protein import by plastids are beginning to emerge - thanks largely to the availability of a total genome sequence for a cyanobacterium. Despite existing for hundreds of millions of years within the plant cell host, the chloroplast endosymbiont retains clear hallmarks of its bacterial ancestry. Plastid division relies on proteins that are also responsible for bacterial division, although may of the genes for these proteins have been confiscated by the host. Plastid protein import on the other hand relies on proteins that seem to have functioned originally as exporters but that have now been persuaded to operate in the reverse direction to traffic proteins from the host cell into the endosymbiont.

Chloroplasts↗
PubMed2004

Escherichia coli evolution during stationary phase.

The process of evolution by natural selection has been known for a century and a half, yet the mechanics of selection are still poorly understood. In most cases where natural selection has been studied, the genetic and physiological bases of fitness variation that result in population changes were not identified, leaving only a partial understanding of selection. Starved cultures of the bacterium Escherichia coli present a model system with which to address the genetic and physiological bases of natural selection. This is a model system that also reflects the prevalent state of bacteria in the natural world; due to intense competition for nutrients, microorganisms spend the majority of their lives under starvation conditions. Genetic analyses of a single survivor of starvation identified four adaptive mutations(1). Investigation of these mutations has revealed insights into the molecular and physiological bases of evolution during prolonged starvation stress.

Adaptation, Biological↗
PubMed1993

Attempts to define distinct parts of NADH:ubiquinone oxidoreductase (complex I).

The NADH:ubiquinone oxidoreductase (complex I) is made up of a peripheral part and a membrane part. The two parts are arranged perpendicular to each other and give the complex an unusual L-shaped structure. The peripheral part protrudes into the matrix space and constitutes the proximal segment of the electron pathway with the NADH-binding site, the FMN and at least three iron-sulfur clusters. The membrane part constitutes the distal segment of the electron pathway with at least one iron-sulfur cluster and the ubiquinone-binding site. Both parts are assembled separately and relationships of the major structural modules of the two parts with different bacterial enzymes suggest, that both parts also emerged independently in evolution. This assumption is further supported by the conserved order of bacterial complex I genes, which correlates with the topological arrangement of the corresponding subunits in the two parts of complex I.

Animals↗
PubMed2006

Probing genomic diversity and evolution of Escherichia coli O157 by single nucleotide polymorphisms.

Infections by Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) are the predominant cause of bloody diarrhea and hemolytic uremic syndrome in the United States. In silico comparison of the two complete STEC O157 genomes (Sakai and EDL933) revealed a strikingly high level of sequence identity in orthologous protein-coding genes, limiting the use of nucleotide sequences to study the evolution and epidemiology of this bacterial pathogen. To systematically examine single nucleotide polymorphisms (SNPs) at a genome scale, we designed comparative genome sequencing microarrays and analyzed 1199 chromosomal genes (a total of 1,167,948 bp) and 92,721 bp of the large virulence plasmid (pO157) of eleven outbreak-associated STEC O157 strains. We discovered 906 SNPs in 523 chromosomal genes and observed a high level of DNA polymorphisms among the pO157 plasmids. Based on a uniform rate of synonymous substitution for Escherichia coli and Salmonella enterica (4.7x10(-9) per site per year), we estimate that the most recent common ancestor of the contemporary beta-glucuronidase-negative, non-sorbitolfermenting STEC O157 strains existed ca. 40 thousand years ago. The phylogeny of the STEC O157 strains based on the informative synonymous SNPs was compared to the maximum parsimony trees inferred from pulsed-field gel electrophoresis and multilocus variable numbers of tandem repeats analysis. The topological discrepancies indicate that, in contrast to the synonymous mutations, parts of STEC O157 genomes have evolved through different mechanisms with highly variable divergence rates. The SNP loci reported here will provide useful genetic markers for developing high-throughput methods for fine-resolution genotyping of STEC O157. Functional characterization of nucleotide polymorphisms should shed new insights on the evolution, epidemiology, and pathogenesis of STEC O157 and related pathogens.

Chromosome Mapping↗
PubMed1995

Relationship between evolutionary rate and cellular location among the Inv/Spa invasion proteins of Salmonella enterica.

For 21 strains of Salmonella enterica, nucleotide sequences were obtained for three invasion genes, spaO, spaP, and spaQ, of the chromosomal inv/spa complex, the products of which form a protein export system required for entry of the bacteria into nonphagocytic host cells. These genes are present in all eight subspecies of the salmonellae, and homologues occur in a variety of other bacteria, including the enteric pathogens Shigella and Yersinia, in which they are plasmid borne. Evolutionary diversification of the invasion genes among the subspecies of S. enterica has been generally similar in pattern and average rate to that of housekeeping genes. However, the range of variation in evolutionary rate among the invasion genes is unusually large, and there is a relationship between the evolutionary rate and cellular location of the invasion proteins, possibly reflecting diversifying selection on exported proteins in adaptation to variable host factors in extracellular environments. The SpaO protein, which is hypervariable in S. enterica and exhibits only 24% sequence identity with its homologues in Shigella and Yersinia, is secreted. In contrast, the membrane-associated proteins SpaP, SpaQ, and InvA are weakly polymorphic and have > 60% sequence identity with the corresponding proteins of other enteric bacteria. Acquisition of the inv/spa genes may have been a key event in the evolution of the salmonellae as pathogens, following which the invention of flagellar phase shifting facilitated niche expansion to include warm-blooded vertebrates.

Adhesins, Bacterial↗
PubMed2006

Evolution of paralogous genes: Reconstruction of genome rearrangements through comparison of multiple genomes within Staphylococcus aureus.

Analysis of evolution of paralogous genes in a genome is central to our understanding of genome evolution. Comparison of closely related bacterial genomes, which has provided clues as to how genome sequences evolve under natural conditions, would help in such an analysis. With species Staphylococcus aureus, whole-genome sequences have been decoded for seven strains. We compared their DNA sequences to detect large genome polymorphisms and to deduce mechanisms of genome rearrangements that have formed each of them. We first compared strains N315 and Mu50, which make one of the most closely related strain pairs, at the single-nucleotide resolution to catalogue all the middle-sized (more than 10 bp) to large genome polymorphisms such as indels and substitutions. These polymorphisms include two paralogous gene sets, one in a tandem paralogue gene cluster for toxins in a genomic island and the other in a ribosomal RNA operon. We also focused on two other tandem paralogue gene clusters and type I restriction-modification (RM) genes on the genomic islands. Then we reconstructed rearrangement events responsible for these polymorphisms, in the paralogous genes and the others, with reference to the other five genomes. For the tandem paralogue gene clusters, we were able to infer sequences for homologous recombination generating the change in the repeat number. These sequences were conserved among the repeated paralogous units likely because of their functional importance. The sequence specificity (S) subunit of type I RM systems showed recombination, likely at the homology of a conserved region, between the two variable regions for sequence specificity. We also noticed novel alleles in the ribosomal RNA operons and suggested a role for illegitimate recombination in their formation. These results revealed importance of recombination involving long conserved sequence in the evolution of paralogous genes in the genome.

Amino Acid Sequence↗
PubMed2006

Clonal adaptive radiation in a constant environment.

The evolution of new combinations of bacterial properties contributes to biodiversity and the emergence of new diseases. We investigated the capacity for bacterial divergence with a chemostat culture of Escherichia coli. A clonal population radiated into more than five phenotypic clusters within 26 days, with multiple variations in global regulation, metabolic strategies, surface properties, and nutrient permeability pathways. Most isolates belonged to a single ecotype, and neither periodic selection events nor ecological competition for a single niche prevented an adaptive radiation with a single resource. The multidirectional exploration of fitness space is an underestimated ingredient to bacterial success even in unstructured environments.

Adaptation, Physiological↗
PubMed2001

Comparable system-level organization of Archaea and Eukaryotes.

A central and long-standing issue in evolutionary theory is the origin of the biological variation upon which natural selection acts. Some hypotheses suggest that evolutionary change represents an adaptation to the surrounding environment within the constraints of an organism's innate characteristics. Elucidation of the origin and evolutionary relationship of species has been complemented by nucleotide sequence and gene content analyses, with profound implications for recognizing life's major domains. Understanding of evolutionary relationships may be further expanded by comparing systemic higher-level organization among species. Here we employ multivariate analyses to evaluate the biochemical reaction pathways characterizing 43 species. Comparison of the information transfer pathways of Archaea and Eukaryotes indicates a close relationship between these domains. In addition, whereas eukaryotic metabolic enzymes are primarily of bacterial origin, the pathway-level organization of archaeal and eukaryotic metabolic networks is more closely related. Our analyses therefore suggest that during the symbiotic evolution of eukaryotes, incorporation of bacterial metabolic enzymes into the proto-archaeal proteome was constrained by the host's pre-existing metabolic architecture.

Archaea↗
PubMed2003

Signal sequence conservation and mature peptide divergence within subgroups of the murine beta-defensin gene family.

Beta-defensins are two exon genes which encode broad spectrum antimicrobial cationic peptides. We have analyzed the largest murine cluster of these genes which localizes to chromosome 8. Using hidden Markov models, we identified six beta-defensin exon 2-like sequences and subsequently found full-length expressed transcripts for these novel genes. Expression was high in brain and reproductive tissues. Eleven beta-defensins could be grouped into two clear subgroups by virtue of their position and high signal sequence (exon 1 encoded) identity. In contrast, however, there was a very low level of sequence conservation in the exon 2 region encoding the mature antimicrobial peptide. Examination of the gene sequences of orthologs in other rodents also revealed an excess of nucleotide changes that altered amino acids in the mature peptide region. Evolutionary analysis revealed strong evidence that following gene duplication, exon 1 and surrounding noncoding DNA show little divergence within subgroups. The focus for rapid sequence divergence is localized in the DNA encoding the mature peptide and this is driven by accelerated positive selection. This mechanism of evolution is consistent with the role of this gene family as defense against bacterial pathogens and the sequence changes have implications for novel antibiotic design.

Animals↗