Search results for "SYMBIOSIS"
showing 10 items of 627 documents
GroEL and the maintenance of bacterial endosymbiosis
2004
Many eukaryotic organisms have symbiotic associations with obligate intracellular bacteria. The clonal transmission of endosymbionts between host generations should lead to the irreversible fixation of slightly deleterious mutations in their non-recombinant genome by genetic drift. However, the stability of endosymbiosis indicates that some mechanism is involved in the amelioration of the effects of these mutations. We propose that the chaperone GroEL was involved in the acquisition of an endosymbiotic lifestyle not only by means of its over-production, as proposed by Moran, but also by its adaptive evolution mediated by positive selection to improve the interaction with the unstable endosy…
Why are the genomes of endosymbiotic bacteria so stable?
2003
The comparative analysis of three strains of the endosymbiotic bacterium Buchnera aphidicola has revealed high genome stability associated with an almost complete absence of chromosomal rearrangements and horizontal gene transfer events during the past 150 million years. The loss of genes involved in DNA uptake and recombination in the initial stages of endosymbiosis probably underlies this stability. Gene loss, which was extensive during the initial steps of Buchnera evolution, has continued in the different Buchnera lineages since their divergence.
The IStron CdISt1 of Clostridium difficile: molecular symbiosis of a group I intron and an insertion element
2003
Abstract The IStron CdISt1 was first discovered as an insertion into the tcdA gene of the clinical isolate C34. It combines structural and functional properties of a group I intron at its 5′-end with those of an insertion element at its 3′-end. Up to date four different types could be found, mainly differing in their IS-element portions. Contrasting classical group I introns, CdISt1 is always integrated in ORFs encoding bacterial protein. In case CdISt1 had only the IS-element function such insertion would inactivate the protein encoded by the host gene. It is only due to the self-splicing activity of the group I intron parts that CdISt1 integration does not abolish protein function. Both e…
Plasmids in the aphid endosymbiont Buchnera aphidicola with the smallest genomes. A puzzling evolutionary story
2006
Buchnera aphidicola, the primary endosymbiont of aphids, has undergone important genomic and biochemical changes as an adaptation to intracellular life. The most important structural changes include a drastic genome reduction and the amplification of genes encoding key enzymes for the biosynthesis of amino acids by their translocation to plasmids. Molecular characterization through different aphid subfamilies has revealed that the genes involved in leucine and tryptophan biosynthesis show a variable fate, since they can be located on plasmids or on the chromosome in different lineages. This versatility contrasts with the genomic stasis found in three distantly related B. aphidicola strains …
Complete Genome Sequence of “Candidatus Tremblaya princeps” Strain PCVAL, an Intriguing Translational Machine below the Living-Cell Status
2011
ABSTRACT The sequence of the genome of “ Candidatus Tremblaya princeps” strain PCVAL, the primary endosymbiont of the citrus mealybug Planococcus citri , has been determined. “ Ca . Tremblaya princeps” presents an unusual nested endosymbiosis and harbors a gammaproteobacterial symbiont within its cytoplasm in all analyzed mealybugs. The genome sequence reveals that “ Ca . Tremblaya princeps” cannot be considered an independent organism but that the consortium with its gammaproteobacterial symbiotic associate represents a new composite living being.
Adaptive evolution in GroEL from distantly related endosymbiotic bacteria of insects
2005
Many symbioses between bacteria and insects resulted from ancient infections followed by strict vertical transmission within host lineages. The strong bottlenecks under which this transmission occurs promote the neutral fixation of slightly deleterious mutations by genetic drift. As predicted by Muller's ratchet, this fixation will drive endosymbiotic bacteria through an irreversible dynamics of fitness loss. The chaperonin GroEL has been proposed as a compensatory mechanism whereby endosymbiotic bacteria of aphids persist. Here, we show that endosymbiotic bacteria of insects from two phylogenetically very distant bacterial phyla have fixed amino acid substitutions by positive selection in …
Signalling between arbuscular mycorrhizal fungi and plants: Identification of a gene expressed during early interactions by differential RNA display …
2002
Although there is evidence for an interplay of signalling/recognition events at different stages during plant/fungal interactions in arbuscular mycorrhiza, the nature of signalling molecules and signal perception/transduction processes are so far unknown. Virtually nothing is known of molecular interactions during initial contact between arbuscular mycorrhizal symbionts, but plant mutants which limit fungal development to these first steps (myc-1) provide proof of the involvement of plant genes. One such pea mutant (P2) has been used to investigate gene expression during early plant-fungal interactions by differential RNA display. Partial transcriptome analysis has indicated frequent simila…
Comparative Genomics of Serratia spp.: Two Paths towards Endosymbiotic Life
2012
Symbiosis is a widespread phenomenon in nature, in which insects show a great number of these associations. Buchnera aphidicola, the obligate endosymbiont of aphids, coexists in some species with another intracellular bacterium, Serratia symbiotica. Of particular interest is the case of the cedar aphid Cinara cedri, where B. aphidicola BCc and S. symbiotica SCc need each other to fulfil their symbiotic role with the insect. Moreover, various features seem to indicate that S. symbiotica SCc is closer to an obligate endosymbiont than to other facultative S. symbiotica, such as the one described for the aphid Acirthosyphon pisum (S. symbiotica SAp). This work is based on the comparative genomi…
Genetic Variability of Hepatitis C Virus before and after Combined Therapy of Interferon plus Ribavirin
2008
We present an analysis of the selective forces acting on two hepatitis C virus genome regions previously postulated to be involved in the viral response to combined antiviral therapy. One includes the three hypervariable regions in the envelope E2 glycoprotein, and the other encompasses the PKR binding domain and the V3 domain in the NS5A region. We used a cohort of 22 non-responder patients to combined therapy (interferon alpha-2a plus ribavirin) for which samples were obtained before initiation of therapy and after 6 or/and 12 months of treatment. A range of 25-100 clones per patient, genome region and time sample were sequenced. These were used to detect general patterns of adaptation, t…
Compatibility of Rhizobial Genotypes within Natural Populations of Rhizobium leguminosarum Biovar viciae for Nodulation of Host Legumes
2003
ABSTRACT Populations of Rhizobium leguminosarum biovar viciae were sampled from two bulk soils, rhizosphere, and nodules of host legumes, fava bean ( Vicia faba ) and pea ( Pisum sativum ) grown in the same soils. Additional populations nodulating peas, fava beans, and vetches ( Vicia sativa ) grown in other soils and fava bean-nodulating strains from various geographic sites were also analyzed. The rhizobia were characterized by repetitive extragenomic palindromic-PCR fingerprinting and/or PCR-restriction fragment length polymorphism (RFLP) of 16S-23S ribosomal DNA intergenic spacers as markers of the genomic background and PCR-RFLP of a nodulation gene region, nodD , as a marker of the sy…