Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SYMBIOSIS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed2006

Leeches and their microbiota: naturally simple symbiosis models.

Strictly blood-feeding leeches and their limited microbiota provide natural and powerful model systems to examine symbiosis. Blood is devoid of essential nutrients and it is thought that symbiotic bacteria synthesize these for the host. In this review, three distinct leech-microbe associations are described: (i) the mycetome, which is the large symbiont-containing organ associated with the esophagus; (ii) the nephridia and bladders that form the excretory system; and (iii) the digestive tract, where two bacterial species dominate the microbiota. The current knowledge and features of leech biology that promote the investigation of interspecific interactions (host-microbe and microbe-microbe) and their evolution are highlighted.

Animals↗
PubMed2006

Multiple origins of the ascidian-Prochloron symbiosis: molecular phylogeny of photosymbiotic and non-symbiotic colonial ascidians inferred from 18S rDNA sequences.

In the tropics, certain didemnid ascidians harbor the prokaryotic photosymbiont Prochloron. To date, this photosymbiosis has been found in four didemnid genera that include non-symbiotic species. Here, we report the molecular phylogeny of symbiotic and non-symbiotic didemnids based on their 18S rDNA sequences. The data cover all four genera containing symbiotic species and one other genus comprised of only non-symbiotic species. Near-complete nucleotide sequences of 18S rDNAs were determined for four non-didemnid species and 52 didemnid samples (five genera), including 48 photosymbiotic samples collected from the Ryukyu Archipelago, the Great Barrier Reef, Hawaii, and Bali. Our phylogenetic trees indicated a monophyletic origin of the family Didemnidae, as well as each of the didemnid genera. The results strongly support the hypothesis that establishment of the ascidian-Prochloron symbiosis occurred independently in the Didemnidae lineage at least once in each of the genera that possess symbiotic species.

Animals↗
PubMed2001

Metals and the rhizobial-legume symbiosis--uptake, utilization and signalling.

In this review, we consider how the nitrogen-fixing root nodule bacteria, the 'rhizobia', acquire various metals, paying particular attention to the uptake of iron. We also review the literature pertaining to the roles of molybdenum and nickel in the symbiosis with legumes. We highlight some gaps in our knowledge, for example the lack of information on how rhizobia acquire molybdenum. We examine the means whereby different metals affect rhizobial physiology and the role of metals as signals for gene regulation. We describe the ways in which genetics has shown (or not) if, and how, particular metal uptake and/or metal-mediated signalling pathways are required for the symbiotic interaction with legumes.

Fabaceae↗
PubMed2002

A novel bioremediation system for heavy metals using the symbiosis between leguminous plant and genetically engineered rhizobia.

A novel plant-bacterial remediation system for heavy metals (HM) was developed by expression of tetrameric human metallothionein (MTL4) in Mesorhizobium huakuii subsp. rengei B3, a strain which infects and forms nodules on a green manure, Astragalus sinicus. The MTL4 gene was fused to the nifH and nolB promoters, which generated nodule- specific expression of the MTL4 gene. The expression analysis of the MTL4 gene was demonstrated in free-living cells in the presence of Cd(2+) and Cu(2+), under the low oxygen condition. The MTL4 under the nifH and nolB promoters was expressed and increased the accumulation of Cd(2+), but not Cu(2+) in free-living cells. The expression of the integrated nifH-MTL4 gene in the chromosome of strain B3 was also expressed stably and accumulated Cd(2+) in the bacterial cells. The MTL4 transcripts were detected by in situ hybridization in bacteroids of mature nodules of A. sinicus containing nifH-MTL4 and nolB-MTL4 fusion gene. Moreover the MTL4 protein was detected by immunostaining. By infection of the recombinant B3, A. sinicus established symbiosis with the recombinant B3 that was grown in Cd(2+) and Cu(2+)-polluted soils. The symbionts increased Cd(2+) accumulation in nodules 1.7-2.0-fold, whereas, no significantly increase in Cu(2+) accumulation was noted.

Astragalus Plant↗
PubMed2000

Common molecular mechanisms of symbiosis and pathogenesis.

Traditionally, symbiotic and pathogenic interactions were considered different manifestations of the bacteria-host interaction. However, the molecular mechanisms that mediate communication between and cellular modulation of the involved partners are quite similar. With this review we aim to contribute to a reduction of the traditional gap between symbiosis and pathogenesis research.

Animals↗
PubMed2001

Genetics and genomics of root symbiosis.

Model genetics and genomics have been developed as tools for studying the third largest family of flowering plants, the Leguminosae, which includes important crop plants. Functional genomics strategies for the global analysis of gene expression, the elucidation of pathways and reverse genetics are established. These approaches provide new possibilities for investigating rhizobial as well as mycorrhizal endosymbiosis. Plant genes with central functions in these mutualistic interactions have been identified by positional cloning and gene tagging. With progress in Lotus japonicus genome sequencing, which was recently initiated by Japanese researchers, comparative genomics will contribute to our understanding of symbiosis, pathogenesis and the evolution of plant genomes.

Fabaceae↗
PubMed2003

Signaling in symbiosis.

In recent years, the major focus in nodulation research has been on the genetic dissection of Nod-factor signaling. Components of this pathway appear to be shared with signaling processes that are induced during the formation of mycorrhiza. With the cloning of orthologs of the NIN and DMI2 genes from several legumes, the molecular characteristics of components of the Nod-factor-signaling pathway are now starting to be revealed. Orthologs of HAR1, a key player in the systemic autoregulatory mechanism controlling nodule numbers, have also been cloned recently. The mechanism by which nodulation is autoregulated is related to that by which fixed nitrogen inhibits nodulation. Genes that are involved in Nod-factor signaling may be targets for mechanisms that suppress nodulation. If this is the case, it would bring two fascinating areas of symbiosis together.

Nitrogen Fixation↗
PubMed1999

Bacteroid formation in the Rhizobium-legume symbiosis.

During the Rhizobium-legume symbiosis, bacteria enter the cells of host plants and differentiate into nitrogen-fixing bacteroids. Recent mutant screens and expression studies have revealed bacterial genes involved in the developmental pathway and demonstrate how the genetic requirements can vary from one host-microbe system to another. Whether bacteroids are terminally differentiated cells is an ongoing debate and new experimental systems are required to address this issue.

Fabaceae↗
PubMed1997

Emergence of symbiosis in peptide self-replication through a hypercyclic network.

Symbiosis is an association between different organisms that leads to a reciprocal enhancement of their ability to survive. Similar mutually beneficial relationships can operate at the molecular level in the form of a hypercycle, a collective of two or more self-replicating species interlinked through a cyclic catalytic network. The superposition of cross-catalysis onto autocatalytic replication integrates the members of the hypercycle into a single system that reproduces through a second-order (or higher) form of nonlinear autocatalysis. The hypercycle population as a whole is therefore able to compete more efficiently for existing resources than any one member on its own. In addition, the effects of beneficial mutations of any one member are spread over the entire population. The formation of hypercycles has been suggested as an important step in the transition from inanimate to living chemistry, and a large number of hypercycles are expected to be embedded within the complex networks of living systems. But only one naturally occurring hypercycle has been well documented, while two autocatalytic chemical systems may contain vestiges of hypercyclic organization. Here we report a chemical system that constitutes a clear example of a minimal hypercyclic network, in which two otherwise competitive self-replicating peptides symbiotically catalyse each others' production.

Amino Acid Sequence↗
PubMed2003

Amino-acid cycling drives nitrogen fixation in the legume-Rhizobium symbiosis.

The biological reduction of atmospheric N2 to ammonium (nitrogen fixation) provides about 65% of the biosphere's available nitrogen. Most of this ammonium is contributed by legume-rhizobia symbioses, which are initiated by the infection of legume hosts by bacteria (rhizobia), resulting in formation of root nodules. Within the nodules, rhizobia are found as bacteroids, which perform the nitrogen fixation: to do this, they obtain sources of carbon and energy from the plant, in the form of dicarboxylic acids. It has been thought that, in return, bacteroids simply provide the plant with ammonium. But here we show that a more complex amino-acid cycle is essential for symbiotic nitrogen fixation by Rhizobium in pea nodules. The plant provides amino acids to the bacteroids, enabling them to shut down their ammonium assimilation. In return, bacteroids act like plant organelles to cycle amino acids back to the plant for asparagine synthesis. The mutual dependence of this exchange prevents the symbiosis being dominated by the plant, and provides a selective pressure for the evolution of mutualism.

Amino Acids↗
PubMed2005

Nitrogen transfer in the arbuscular mycorrhizal symbiosis.

Most land plants are symbiotic with arbuscular mycorrhizal fungi (AMF), which take up mineral nutrients from the soil and exchange them with plants for photosynthetically fixed carbon. This exchange is a significant factor in global nutrient cycles as well as in the ecology, evolution and physiology of plants. Despite its importance as a nutrient, very little is known about how AMF take up nitrogen and transfer it to their host plants. Here we report the results of stable isotope labelling experiments showing that inorganic nitrogen taken up by the fungus outside the roots is incorporated into amino acids, translocated from the extraradical to the intraradical mycelium as arginine, but transferred to the plant without carbon. Consistent with this mechanism, the genes of primary nitrogen assimilation are preferentially expressed in the extraradical tissues, whereas genes associated with arginine breakdown are more highly expressed in the intraradical mycelium. Strong changes in the expression of these genes in response to nitrogen availability and form also support the operation of this novel metabolic pathway in the arbuscular mycorrhizal symbiosis.

Acetates↗
PubMed2026

Yellow protein co-opted to sustain obligate symbiosis in leaf beetles.

Yellow proteins are best known for their roles in pigmentation, behavior, and development across insects. Here, we uncover their striking evolutionary co-option for a wholly distinct function: sustaining a Paleocene-aged digestive symbiosis in tortoise beetles. We show that a female-specific Yellow forms the gelatinous spheres that encapsulate the bacterium Stammera during vertical transmission, allowing it to subsist extracellularly despite its drastically reduced genome (0.24 Mb) and limited metabolic capacity. Yellow expression is highly localized to symbiont-harboring glands in the ovaries, where the protein is assembled into a matrix and secreted during egg-laying. Functional knockdown of yellow disrupts sphere integrity and compromises symbiont viability under dry conditions, underscoring the protein's embedding properties and protective role for Stammera. These findings reveal a novel function for an ancient gene family and demonstrate how tortoise beetles have repurposed Yellows to overcome the extreme metabolic constraints faced by their symbionts during extracellular transmission.

Animals↗
PubMed2003

Analysis of the legume-rhizobia symbiosis in shrubs from central western Spain.

AIMS: This work analyses the diversity of rhizobia associated with some of the predominant shrubby legumes in central-western Spain. Symbiotic promiscuity and effectiveness were studied using cross-inoculation experiments with shrubby species. MATERIAL AND RESULTS: Six new bradyrhizobia strains were isolated from nodules collected from wild plants of six leguminous species, Cytisus balansae, C. multiflorus, C. scoparius, C. striatus, Genista hystrix and Retama sphaerocarpa. These isolates were genetically characterized by 16S rDNA partial sequencing and random amplification of polymorphic DNA-PCR fingerprinting. The phylogenetic analysis revealed that these isolates could represent three new Bradyrhizobium species. Shrubby legumes and bradyrhizobia displayed a high symbiotic promiscuity both for infectivity and effectiveness. Symbioses were effective in more than 70% of the associations established by four of the six plant species. CONCLUSIONS: Native woody legumes in western Spain are nodulated by Bradyrhizobium strains. The high degree of symbiotic promiscuity and effectiveness highlights the complex dynamics of these communities in wild ecosystems under a Mediterranean-type climate. Furthermore, the results from this study suggest a potential importance of inoculation for these legume species in soil-restoration projects. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study, to our knowledge, that combines both molecular analysis and pot trials to study the rhizobia-legume symbiosis for wild legumes.

Biomass↗
PubMed2000

Critical protective role of bacterial superoxide dismutase in rhizobium-legume symbiosis.

In nitrogen-poor soils, rhizobia elicit nodule formation on legume roots, within which they differentiate into bacteroids that fix atmospheric nitrogen. Protection against reactive oxygen species (ROS) was anticipated to play an important role in Rhizobium-legume symbiosis because nitrogenase is extremely oxygen sensitive. We deleted the sodA gene encoding the sole cytoplasmic superoxide dismutase (SOD) of Sinorhizobium meliloti. The resulting mutant, deficient in superoxide dismutase, grew almost normally and was only moderately sensitive to oxidative stress when free living. In contrast, its symbiotic properties in alfalfa were drastically affected. Nitrogen-fixing ability was severely impaired. More strikingly, most SOD-deficient bacteria did not reach the differentiation stage of nitrogen-fixing bacteroids. The SOD-deficient mutant nodulated poorly and displayed abnormal infection. After release into plant cells, a large number of bacteria failed to differentiate into bacteroids and rapidly underwent senescence. Thus, bacterial SOD plays a key protective role in the symbiotic process.

Bacterial Proteins↗
PubMed2002

The Sinorhizobium meliloti stringent response affects multiple aspects of symbiosis.

Sinorhizobium meliloti and host legumes enter into a nitrogen-fixing, symbiotic relationship triggered by an exchange of signals between bacteria and plant. S. meliloti produces Nod factor, which elicits the formation of nodules on plant roots, and succinoglycan, an exopolysaccharide that allows for bacterial invasion and colonization of the host. The biosynthesis of these molecules is well defined, but the specific regulation of these compounds is not completely understood. Bacteria control complex regulatory networks by the production of ppGpp, the effector molecule of the stringent response, which induces physiological change in response to adverse growth conditions and can also control bacterial development and virulence. Through detailed analysis of an S. meliloti mutant incapable of producing ppGpp, we show that the stringent response is required for nodule formation and regulates the production of succinoglycan. Although it remains unknown whether these phenotypes are connected, we have isolated suppressor strains that restore both defects and potentially identify key downstream regulatory genes. These results indicate that the S. meliloti stringent response has roles in both succinoglycan production and nodule formation and, more importantly, that control of bacterial physiology in response to the plant and surrounding environment is critical to the establishment of a successful symbiosis.

Bacterial Proteins↗
PubMed2003

A delta13C-based carbon flux model for the hydrothermal vent chemoautotrophic symbiosis Riftia pachyptila predicts sizeable CO(2) gradients at the host-symbiont interface.

The chemoautotrophic symbiosis Riftia pachyptila has extremely 13C-enriched delta13C values. Neither isotopic discrimination by the RubisCO enzyme of their bacterial endosymbionts, nor the delta13C value of CO2 at their hydrothermal vent habitat, suffice to explain biomass delta13C values in this organism, which range from - 9 to - 16 per thousand. However, these 13C-enriched delta13C values are consistent with the presence of 13C-enriched CO2 within the symbiont cytoplasm. Such a 13C-enriched pool of CO2 is expected when the rate of CO2 fixation by RubisCO, which fixes 12CO2 more rapidly than 13CO2, approaches the rate of exchange between intracellular and extracellular CO2 pools. Rapid CO2 fixation rates will also generate concentration gradients between these two pools. In order to estimate the size of these concentration gradients, an equation was derived, which describes the delta13C of tubeworm biomass in terms of the size of the CO2 gradient between the hydrothermal vent environment and the symbiont cytoplasm. Using mass balance equations for CO2 exchange and fixation by the symbionts and the tubeworm host, this model predicts that a CO2 concentration gradient of up to 17-fold between the symbiont cytoplasm and the environment is sufficient to explain even the most 13C-enriched R. pachyptila biomass. This model illustrates how both physical and enzymatic factors can act to influence the delta13C of intracellular CO2, which, in turn, highlights the danger of assigning a carbon fixation pathway to an autotroph based solely on its biomass delta13C value.

Animals↗
PubMed2005

Herbivores cause a rapid increase in hereditary symbiosis and alter plant community composition.

Microbial symbioses are ubiquitous in nature. Hereditary symbionts warrant particular attention because of their direct effects on the evolutionary potential of their hosts. In plants, hereditary fungal endophytes can increase the competitive ability, drought tolerance, and herbivore resistance of their host, although it is unclear whether or how these ecological benefits may alter the dynamics of the endophyte symbiosis over time. Here, we demonstrate that herbivores alter the dynamics of a hereditary symbiont under field conditions. Also, we show that changes in symbiont frequency were accompanied by shifts in the overall structure of the plant community. Replicated 25-m2 plots were enriched with seed of the introduced grass, Lolium arundinaceum at an initial frequency of 50% infection by the systemic, seed-transmitted endophyte Neotyphodium coenophialum. Over 54 months, there was a significantly greater increase in endophyte-infection frequency in the presence of herbivores (30% increase) than where mammalian and insect herbivory were experimentally reduced by fencing and insecticide application (12% increase). Under ambient mammalian herbivory, the above-ground biomass of nonhost plant species was reduced compared with the mammal-exclusion treatment, and plant composition shifted toward greater relative biomass of infected, tall fescue grass. These results demonstrate that herbivores can drive plant-microbe dynamics and, in doing so, modify plant community structure directly and indirectly.

Animals↗
PubMed1994

Differential gene expression in an actinorhizal symbiosis: evidence for a nodule-specific cysteine proteinase.

Nodules formed on the roots of actinorhizal plants as a consequence of nitrogen-fixing symbioses with the actinomycete Frankia appear to result from modification of the developmental pathway that leads to lateral root formation. Presently no information exists about factors that control this developmental switch or, until now, about genes that are differentially expressed as a result of an altered developmental pathway. Differential screening of an Alnus glutinosa nodule cDNA library revealed altered levels of gene expression in nodules as compared with roots and allowed isolation of host plant nodule-specific cDNA sequences. The deduced amino acid sequence of one full-length cDNA, AgNOD-CP1, represents a nodule-specific cysteine proteinase similar to cysteine proteinases of the papain superfamily. Residues critical to catalysis, active site, and disulfide bridges are conserved. Suggested roles for this enzyme are as a defense response to Frankia invasion, as a component of tissue remodeling in root and nodule tissues, as a cell cycle component, or as an element of protein turnover. Complexity of hybridization patterns revealed by Southern blot analysis suggests that the gene for AgNOD-CP1 is a member of a multigene family. Northern hybridization results indicate that this gene may have been recruited for a role specific to this symbiosis, a phenomenon observed in the Rhizobium-legume symbioses, perhaps common to many microbe-plant interactions.

Actinomycetales↗