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  • Chemical Engineering  (1,635)
  • Endosymbiosis
  • 1995-1999  (1,644)
  • 1
    Electronic Resource
    Electronic Resource
    Discovery and molecular characterization of a plasmid localized in Buchnera sp. bacterial endosymbiont of the aphid Rhopalosiphum padi (1995)
    Springer
    Journal of molecular evolution 41 (1995), S. 67-73 
    Details
    ISSN: 1432-1432
    Keywords: Aphid ; Endosymbiosis ; Leucine operon ; Buchnera ; Plasmid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have identified and completely sequenced a novel plasmid isolated from the aphid Rhopalosiphum padi. Evidence which suggests that the plasmid occurs localized within the bacterial endosymbionts is presented. The plasmid contains the four genes that constitute the entire leucine operon. This fact makes it really unique since most plasmids are dispensable and lack genes that encode essential anabolic functions. Four more phloem-feeding aphid species also seem to contain homologous plasmids. Although further work is necessary, we hypothesize that this plasmid has appeared during the evolution of the symbiotic association between the aphid and the bacterial endosymbiont. The fact that this plasmid contains the entire leucine operon can be related to physiological evidence showing that the aphid host's diet of plant phloem is deficient in essential amino acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00174042
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  • 2
    Electronic Resource
    Electronic Resource
    Analyses of ribosomal RNA sequences from glaucocystophyte cyanelles provide new insights into the evolutionary relationships of plastids (1995)
    Springer
    Journal of molecular evolution 41 (1995), S. 203-210 
    Details
    ISSN: 1432-1432
    Keywords: Cyanelles ; Cyanophora paradoxa ; Endosymbiosis ; Evolution ; Glaucocystophyta ; Glaucophyta ; Phylogeny ; Plastid ; 16S ribosomal RNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glaucocystophyte algae (sensu Kies, Berl. Deutsch. Bot. Ges. 92, 1979) contain plastids (cyanelles) that retain the peptidoglycan wall of the putative cyanobacterial endosymbiont; this and other ultrastructural characters (e.g., unstacked thylakoids, phycobilisomes) have suggested that cyanelles are “primitive” plastids that may represent undeveloped associations between heterotrophic “host” cells (i.e., glaucocystophytes) and cyanobacteria. To test the monophyly of glaucocystophyte cyanelles and to determine their evolutionary relationship to other plastids, complete 16S ribosomal RNA sequences were determined for Cyanophora paradoxa, Glaucocystis nostochinearum, Glaucosphaera vacuolata, and Gloeochaete wittrockiana. Plastid rRNAs were analyzed with the maximum-likelihood, maximumparsimony, and neighbor joining methods. The phylogenetic analyses show that the cyanelles of C. paradoxa, G. nostochinearum, and G. wittrockiana form a distinct evolutionary lineage; these cyanelles presumably share a monophyletic origin. The rDNA sequence of G. vacuolata was positioned within the nongreen plastid lineage. This result is consistent with analyses of nuclear-encoded rRNAs that identify G. vacuolata as a rhodophyte and support its removal from the Glaucocystophyta. Results of a global search with the maximumlikelihood method suggest that cyanelles are the first divergence among all plastids; this result is consistent with a single loss of the peptidoglycan wall in plastids after the divergence of the cyanelles. User-defined tree analyses with the maximum-likelihood method indicate, however, that the position of the cyanelles is not stable within the rRNA phylogenies. Both maximumparsimony and neighbor-joining analyses showed a close evolutionary relationship between cyanelles and nongreen plastids; these phylogenetic methods were sensitive to inclusion/exclusion of the G. wittrockiana cyanelle sequence. Base compositional bias within the G. wittrockiana 16S rRNA may explain this result. Taken together the phylogenetic analyses are interpreted as supporting a near-simultaneous radiation of cyanelles and green and nongreen plastids; these organelles are all rooted within the cyanobacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170674
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  • 3
    Electronic Resource
    Electronic Resource
    Faster evolutionary rates in endosymbiotic bacteria than in cospeciating insect hosts (1995)
    Springer
    Journal of molecular evolution 41 (1995), S. 727-731 
    Details
    ISSN: 1432-1432
    Keywords: Aphid ; Bacteria ; Buchnera ; Cospeciation ; Endosymbiosis ; Evolutionary rates ; Molecular clock ; Prokaryote ; Ribosomal DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The hypothesis of a universal molecular clock holds that divergent lineages exhibit approximately constant rates of nucleotide substitution over evolutionary time for a particular macromolecule. We compare divergences of ribosomal DNA for aphids (Insecta) and Buchnera, the maternally transmitted, endosymbiotic bacteria that have cospeciated with aphids since initially infecting them over 100 million years ago. Substitution rates average 36 times greater for Buchnera than for their aphid hosts for regions of small-subunit rDNA that are homologous for prokaryotes and eukaryotes. Aphids exhibit 18S rDNA substitution rates that are within the range observed in related insects. In contrast, 16S rDNA evolves about twice as fast in Buchnera as in related free-living bacterial lineages. Nonetheless, the difference between Buchnera and aphids is much greater, suggesting that rates may be generally higher in bacteria. This finding adds to evidence that molecular clocks are only locally rather than universally valid among taxonomic groups. It is consistent with the hypothesis that rates of sequence evolution depend on generation time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00173152
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  • 4
    Electronic Resource
    Electronic Resource
    Free-radical-induced mutation vs redox regulation: Costs and benefits of genes in organelles (1996)
    Springer
    Journal of molecular evolution 42 (1996), S. 482-492 
    Details
    ISSN: 1432-1432
    Keywords: Aging ; Chloroplasts ; Mitochondria ; Cell evolution ; Cytoplasmic genomes ; Gene transfer ; Redox regulation ; Free radical mutagenesis ; Nitrogen fixation ; Endosymbiosis ; Mutation frequency ; Uniparental inheritance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The prokaryotic endosymbionts that became plastids and mitochondria contained genes destined for one of three fates. Genes required for free-living existence were lost. Most genes useful to the symbiosis were transferred to the nucleus of the host. Some genes, a small minority, were retained within the organelle. Here we suggest that a selective advantage of movement of genes to the nucleus is decreased mutation: plastids and mitochondria have high volume-specific rates of redox reactions, producing oxygen free radicals that chemically modify DNA. These mutations lead to synthesis of modified electron carriers that in turn generate more mutagenic free radicals—the “vicious circle” theory of aging. Transfer of genes to the nucleus is also advantageous in facilitating sexual recombination and DNA repair. For genes encoding certain key components of photosynthesis and respiration, direct control of gene expression by redox state of electron carriers may be required to minimize free radical production, providing a selective advantage of organelle location which outweighs that of location in the nucleus. A previous proposal for transfer of genes to the nucleus is an economy of resources in having a single genome and a single apparatus for gene expression, but this argument fails if any organellar gene is retained. A previous proposal for the retention of genes within organelles is that certain proteins are organelle-encoded because they cannot be imported, but there is now evidence against this view. Decreased free radical mutagenesis and increased sexual recombination upon transfer to the nucleus together with redox control of gene expression in organelles may now account for the slightly different gene distributions among nuclei, plastids, and mitochondria found in major eukaryote taxa. This analysis suggests a novel reason for uniparental inheritance of organelles and the evolution of anisogametic sex, and may also account for the occurrence of nitrogen fixation in symbionts rather than in nitrogen-fixing organelles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02352278
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  • 5
    Electronic Resource
    Electronic Resource
    The evolution of the Calvin cycle from prokaryotic to eukaryotic chromosomes: a case study of functional redundancy in ancient pathways through endosymbiosis (1997)
    Springer
    Current genetics 32 (1997), S. 1-18 
    Details
    ISSN: 1432-0983
    Keywords: Key words Chloroplast ; Mitochondria ; Endosymbiosis ; Endosymbiotic gene transfer ; Calvin cycle ; Glycolysis ; Evolution ; Amitochondriate ; Metabolism ; Compartmentation ; Hydrogenosome ; Eukaryote ; Origin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The evolutionary histories of the 12 enzymes that catalyze the reactions of the Calvin cycle in higher-plant chloroplasts are summarized. They are shown to be encoded by a mixture of nuclear genes of cyanobacterial and proteobacterial origin. Moreover, where cytosolic isoforms of these enzymes are found they are almost invariably encoded by genes of clearly endosymbiont origin. We infer that endosymbiosis resulted in functional redundancy that was eliminated through differential gene loss, with intruding eubacterial genes repeatedly replacing pre-existing nuclear counterparts to which they were either functionally or structurally homologous. Our findings fail to support the `product-specificity corollary', which predicts re-targeting of nuclear-encoded gene products to the organelle from whose genome they originated. Rather it would appear that the enzymes of central carbohydrate metabolism have evolved novel targeting possibilities regardless of their origins. Our findings suggest a new hypothesis to explain organelle genome persistence, based on the testable idea that some organelle-encoded gene products might be toxic when present in the cytosol or other inappropriate cellular compartments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002940050241
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  • 6
    Electronic Resource
    Electronic Resource
    Multiple recruitment of class-I aldolase to chloroplasts and eubacterial origin of eukaryotic class-II aldolases revealed by cDNAs from Euglena gracilis (1997)
    Springer
    Current genetics 31 (1997), S. 430-438 
    Details
    ISSN: 1432-0983
    Keywords: Key wordsEuglena gracilis ; Endosymbiosis ; Endosymbiotic gene transfer ; Molecular evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The photosynthetic protist Euglena gracilis is one of few organisms known to possess both class-I and class-II fructose-1,6-bisphosphate aldolases (FBA). We have isolated cDNA clones encoding the precursor of chloroplast class-I FBA and cytosolic class-II FBA from Euglena. Chloroplast class-I FBA is encoded as a single subunit rather than as a polyprotein, its deduced transit peptide of 139 amino acids possesses structural motifs neccessary for precursor import across Euglena's three outer chloroplast membranes. Evolutionary analyses reveal that the class-I FBA of Euglena was recruited to the chloroplast independently from the chloroplast class-I FBA of chlorophytes and may derive from the cytosolic homologue of the secondary chlorophytic endosymbiont. Two distinct subfamilies of class-II FBA genes are shown to exist in eubacteria, which can be traced to an ancient gene duplication which occurred in the common ancestor of contemporary gram-positive and proteobacterial lineages. Subsequent duplications involving eubacterial class-II FBA genes resulted in functional specialization of the encoded products for substrates other than fructose-1,6-bisphosphate. Class-II FBA genes of Euglena and ascomycetes are shown to be of eubacterial origin, having been acquired via endosymbiotic gene transfer, probably from the antecedants of mitochondria. The data provide evidence for the chimaeric nature of eukaryotic genomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002940050226
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  • 7
    Electronic Resource
    Electronic Resource
    Studies on initiation and development of the partner association inGeosiphon pyriforme (Kütz.) v. Wettstein, a unique endocytobiotic system of a fungus (Glomales) and the cyanobacteriumNostoc punctiforme (Kütz.) Hariot (1996)
    Springer
    Protoplasma 193 (1996), S. 3-9 
    Details
    ISSN: 1615-6102
    Keywords: Cyanobacteria ; Endocytobiosis ; Endosymbiosis ; Geosiphon ; Nostoc ; Phagocytosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Phagocytosis ofNostoc filaments byGeosiphon, a fungus closely related to AM forming Glomales, was observed under light microscopes. Incorporation can only be performed ifNostoc primordia come into contact with growing hyphal tips of the fungus. The fungal wall just below the apex softens, and fungal cytoplasm is bulged out repeatedly covering the vegetativeNostoc cells but not the heterocytes. New heterocytes are differentiated by the internalised filament whose cells can increase up to ten times in volume after recovering from incorporation strain. TheNostoc cells are coated stepwise by short finger-shaped protuberances of the fungal hypha. These hernia-like outgrowths first remain separated, after 1 to 2 days they merge. Adjacent hyphal walls inside the complex covering disintegrate. Periphal fungal wall portions are united to form a smooth strong outer envelope. Internalisation is categorised as phagocytosis. The partnership is partly specific,Nostoc strains capable of living endocytobiotically are often partners in other symbioses besidesGeosiphon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01276630
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  • 8
    Electronic Resource
    Electronic Resource
    Structure and expression of the gene encoding ribosomal protein S1 from the cyanobacterium Synechococcus sp. strain PCC 6301: striking sequence similarity to the chloroplast ribosomal protein CS1 (1995)
    Springer
    Molecular genetics and genomics 246 (1995), S. 142-147 
    Details
    ISSN: 1617-4623
    Keywords: ssDNA-binding protein Cyanobacteria ; Ribosomal protein S1 ; Endosymbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We isolated a 38 kDa ssDNA-binding protein from the unicellular cyanobacterium Synechococcus sp. strain PCC 6301 and determined its N-terminal amino acid sequence. A genomic clone encoding the 38 kDa protein was isolated by using a degenerate oligonucleotide probe based on the amino acid sequence. The nucleotide sequence and predicted amino acid sequence revealed that the 38 kDa protein is 306 amino acids long and homologous to the nuclear-encoded 370 amino acid chloroplast ribosomal protein CS1 of spinach (48% identity), therefore identifying it as ribosomal protein (r-protein) S1. Cyanobacterial and chloroplast S1 proteins differ in size from Escherichia coli r-protein S1 (557 amino acids). This provides an additional evidence that cyanobacteria are closely related to chloroplasts. The Synechococcus gene rps1 encoding S1 is located 1.1 kb downstream from psbB, which encodes the photosystem 11 P680 chlorophyll a apoprotein. An open reading frame encoding a potential protein of 168 amino acids is present between psbB and rps1 and its deduced amino acid sequence is similar to that of E. coli hypothetical 17.2 kDa protein. Northern blot analysis showed that rps1 is transcribed as a monocistronic mRNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00294676
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  • 9
    Electronic Resource
    Electronic Resource
    Cloning and characterization of endosymbiotic algae isolated fromParamecium bursaria (1998)
    Springer
    Protoplasma 203 (1998), S. 91-99 
    Details
    ISSN: 1615-6102
    Keywords: Chlorella sp. ; Endosymbiosis ; Infection ; Paramecium bursaria ; Paraquat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The green parameciumParamecium bursaria has many endosymbiotic algae in its cytoplasm. Here, we cloned and characterized endosymbiotic algae fromP. bursaria and examined in detail the interaction between the cloned algae and algae-free paramecia. Homogenates ofP. bursaria were cultured on agar plates containing various kinds of media to establish clones of the endosymbiotic algae. Many algal colonies were obtained from poorly nutritious medium (CA medium) after one month in culture. Algae were picked up from these colonies and inoculations were repeated 9 times on agar plates containing CA medium. On enriched media including bacto-peptone, glucose, proteose-peptone and/or yeast extract, however, bacteria and mold grew rapidly and no algal colonies were formed. When the cloned algae were cultured in liquid CA medium, they grew faster than on agar plates and the numbers stayed constant at 1 × 107 algae/ml after 7 days in culture. They revealed high infectivity to algae-free paramecia, and an incubation period of 24 h and at least 1 × 103 algae/paramecium were required to achieve successful infection (80–90%). The growth and infection rate did not change through 74 repeated inoculations of algae in liquid CA medium. Optical microscopic observations revealed marked morphological similarity between endosymbiotic algae and free-livingChlorella, but the latter showed no infectivity to algae-free paramecia. The cloned endosymbiotic algae presented here will provide an excellent opportunity to examine the mechanism of symbiont-host interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280591
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  • 10
    Electronic Resource
    Electronic Resource
    Compatibility of poly(ethylene 2,6-naphthalate) and poly(butylene 2,6-naphthalate) blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1807-1810 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends prepared from poly(ethylene 2,6-naphthalate) (PEN) and poly(butylene 2,6-naphthalate) (PBN) show only partial miscibility judged from their glass transition temperatures. Two distinct mechanical behaviors are observed: brittle for the blends 〈 20 wt% of PBN, while ductile 〉 20 wt% of PBN. The experimental modulus and strength values of the blends are within the predicted values according to Kleiner and Paul models, respectively. This means that PEN/PBN blends are somewhat compatible based on their tensile properties. Especially for 20 wt% of PBN blend, the high modulus and strength are observed. The viscosity of the blend is high, which may imply a somewhat entangled morphology in the amorphous state.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760352210
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