Specific Symbiosis Research Articles

Partner switching and metabolic flux in a model cnidarian-dinoflagellate symbiosis.

Metabolite exchange is fundamental to the viability of the cnidarian-Symbiodiniaceae symbiosis and survival of coral reefs. Coral holobiont tolerance to environmental change might be achieved through changes in Symbiodiniaceae species composition, but differences in the metabolites supplied by different Symbiodiniaceae species could influence holobiont fitness. Using 13C stable-isotope labelling coupled to gas chromatography-mass spectrometry, we characterized newly fixed carbon fate in the model cnidarian Exaiptasia pallida (Aiptasia) when experimentally colonized with either native Breviolum minutum or non-native Durusdinium trenchii Relative to anemones containing B. minutum, D. trenchii-colonized hosts exhibited a 4.5-fold reduction in 13C-labelled glucose and reduced abundance and diversity of 13C-labelled carbohydrates and lipogenesis precursors, indicating symbiont species-specific modifications to carbohydrate availability and lipid storage. Mapping carbon fate also revealed significant alterations to host molecular signalling pathways. In particular, D. trenchii-colonized hosts exhibited a 40-fold reduction in 13C-labelled scyllo-inositol, a potential interpartner signalling molecule in symbiosis specificity. 13C-labelling also highlighted differential antioxidant- and ammonium-producing pathway activities, suggesting physiological responses to different symbiont species. Such differences in symbiont metabolite contribution and host utilization may limit the proliferation of stress-driven symbioses; this contributes valuable information towards future scenarios that select in favour of less-competent symbionts in response to environmental change.

Symbiosis Specificity of the Preceding Host Plant Can Dominate but Not Obliterate the Association Between Wheat and Its Arbuscular Mycorrhizal Fungal Partners.

The symbiosis established between arbuscular mycorrhizal fungi (AMF) and roots of most land plants plays a key role in plant nutrient acquisition and alleviation of environmental stresses. Despite the ubiquity of the symbiosis, AMF and host species display significant specificity in their interactions. To clarify preferential associations between wheat (Triticum aestivum) and AMF, we characterized root AMF communities in the transition from two first host species, ryegrass (Lolium rigidum) and yellow-serradella (Ornithopus compressus), grown separately or together, to a second host (wheat), by sequencing the large subunit ribosomal DNA (LSU rDNA) gene. The response of AMF communities in wheat to prior soil disturbance – and consequently of the mycelial network [intact extraradical mycelium (ERM) vs. disrupted mycelium] established with either of the first hosts – was also investigated. Since the outcome of a specific host–symbiont interaction depends on the molecular responses of the host plant upon microbial colonization, we studied the expression of six key symbiosis-related genes in wheat roots. AMF communities on L. rigidum and O. compressus roots were clearly distinct. Within an undisturbed ERM, wheat AMF communities were similar to that of previous host, and O. compressus-wheat-AMF interactions supported a greater growth of wheat than L. rigidum-wheat-AMF interactions. This effect declined when ERM was disrupted, but generated a greater activation of symbiotic genes in wheat, indicating that plant symbiotic program depends on some extent on the colonizing symbiont propagule type. When a mixture of L. rigidum and O. compressus was planted, the wheat colonization pattern resembled that of O. compressus, although this was not reflected in a greater growth. These results show a lasting effect of previous hosts in shaping wheat AMF communities through an efficient use of the established ERM, although not completely obliterating host–symbiont specificity.

The Use of the Educational Function of Media in Foreign Language Teaching

Abstract The use of mass communication in the field of foreign language teaching is not a new phenomenon, because traditional media have been in use in this area for a few decades. Nowadays, however, several tendencies confirming the scale of this phenomenon can be observed. Mass media, and new media in particular, are used both in the process of self-education and as an important tool used by foreign language teachers. Technological progress, the communication revolution, the spread of the Internet, and the development of new media and mobile technologies offer modern and more effective methods of language education. This article reviews the conditions relating to the relationship between mass media and language learning, taking into account the possibility of using one of the key functions of mass communication, namely its educational function. The authors, using literature analysis, defined and analyzed the causes of specific symbiosis between media tools and technologies as well as the methodology used in the field of foreign language teaching.

Stenotrophomonas-Like Bacteria Are Widespread Symbionts in Cone Snail Venom Ducts.

Cone snails are biomedically important sources of peptide drugs, but it is not known whether snail-associated bacteria affect venom chemistry. To begin to answer this question, we performed 16S rRNA gene amplicon sequencing of eight cone snail species, comparing their microbiomes with each other and with those from a variety of other marine invertebrates. We show that the cone snail microbiome is distinct from those in other marine invertebrates and conserved in specimens from around the world, including the Philippines, Guam, California, and Florida. We found that all venom ducts examined contain diverse 16S rRNA gene sequences bearing closest similarity to Stenotrophomonas bacteria. These sequences represent specific symbionts that live in the lumen of the venom duct, where bioactive venom peptides are synthesized.IMPORTANCE In animals, symbiotic bacteria contribute critically to metabolism. Cone snails are renowned for the production of venoms that are used as medicines and as probes for biological study. In principle, symbiotic bacterial metabolism could either degrade or synthesize active venom components, and previous publications show that bacteria do indeed contribute small molecules to some venoms. Therefore, understanding symbiosis in cone snails will contribute to further drug discovery efforts. Here, we describe an unexpected, specific symbiosis between bacteria and cone snails from around the world.

Tourism and recreation a global threat to orchids

Orchidaceae is a mega diverse family accounting for 10% of the world’s flowering plants. Due to factors such as small dispersed populations, specific symbiosis with fungi and with pollinators and their desirability for collecting, many orchids are threatened with extinction. Tourism and recreation is increasingly recognised as a global threat for plants, but is it an issue for orchids? When data on orchids from the International Union for Nature Conservation (IUCN) Red List was reviewed, we found that 149 (40%) of the 442 orchid species with threat data were at risk from tourism and recreation. This included: 98 (22%) species threatened by residential and commercial development for tourism and recreation, 75 (17%) by intentional collecting within protected areas, and 90 (20%) by human intrusions and disturbance from recreational activities. The three threats often co-occurred and hence can be treated as a threat syndrome. The proportion of species threatened varied among locations with 80% of the 65 species in East Asia, 32% of 68 species in South and Southeast Asia and 94% of 16 orchid species in Europe threatened by tourism and recreation. Terrestrial orchids and those growing in forests were more likely to be at risk from these threats. With so many species at risk, increased awareness and recognition of these threats combined with improved management to reduce impacts is needed. Gaps and inconsistencies in the IUCN Red List must also be addressed to obtain a better understanding of the extent of this, and other threats to plants.

Specificity in Legume-Rhizobia Symbioses.

Most species in the Leguminosae (legume family) can fix atmospheric nitrogen (N2) via symbiotic bacteria (rhizobia) in root nodules. Here, the literature on legume-rhizobia symbioses in field soils was reviewed and genotypically characterised rhizobia related to the taxonomy of the legumes from which they were isolated. The Leguminosae was divided into three sub-families, the Caesalpinioideae, Mimosoideae and Papilionoideae. Bradyrhizobium spp. were the exclusive rhizobial symbionts of species in the Caesalpinioideae, but data are limited. Generally, a range of rhizobia genera nodulated legume species across the two Mimosoideae tribes Ingeae and Mimoseae, but Mimosa spp. show specificity towards Burkholderia in central and southern Brazil, Rhizobium/Ensifer in central Mexico and Cupriavidus in southern Uruguay. These specific symbioses are likely to be at least in part related to the relative occurrence of the potential symbionts in soils of the different regions. Generally, Papilionoideae species were promiscuous in relation to rhizobial symbionts, but specificity for rhizobial genus appears to hold at the tribe level for the Fabeae (Rhizobium), the genus level for Cytisus (Bradyrhizobium), Lupinus (Bradyrhizobium) and the New Zealand native Sophora spp. (Mesorhizobium) and species level for Cicer arietinum (Mesorhizobium), Listia bainesii (Methylobacterium) and Listia angolensis (Microvirga). Specificity for rhizobial species/symbiovar appears to hold for Galega officinalis (Neorhizobium galegeae sv. officinalis), Galega orientalis (Neorhizobium galegeae sv. orientalis), Hedysarum coronarium (Rhizobium sullae), Medicago laciniata (Ensifer meliloti sv. medicaginis), Medicago rigiduloides (Ensifer meliloti sv. rigiduloides) and Trifolium ambiguum (Rhizobium leguminosarum sv. trifolii). Lateral gene transfer of specific symbiosis genes within rhizobial genera is an important mechanism allowing legumes to form symbioses with rhizobia adapted to particular soils. Strain-specific legume rhizobia symbioses can develop in particular habitats.

A specific and widespread association between deep-sea Bathymodiolus mussels and a novel family of Epsilonproteobacteria.

Bathymodiolus mussels dominate animal communities at many hydrothermal vents and cold seeps. Essential to the mussels' ecological and evolutionary success is their association with symbiotic methane- and sulfur-oxidizing gammaproteobacteria, which provide them with nutrition. In addition to these well-known gammaproteobacterial endosymbionts, we found epsilonproteobacterial sequences in metatranscriptomes, metagenomes and 16S rRNA clone libraries as well as by polymerase chain reaction screening of Bathymodiolus species sampled from vents and seeps around the world. These epsilonproteobacterial sequences were closely related, indicating that the association is highly specific. TheBathymodiolus-associated epsilonproteobacterial 16S rRNA sequences were at most 87.6% identical to the closest cultured relative, and 91.2% identical to the closest sequences in public databases. This clade therefore represents a novel family within the Epsilonproteobacteria. Fluorescence in situ hybridization and transmission electron microscopy showed that the bacteria are filamentous epibionts associated with the gill epithelia in two Bathymodiolus species. In animals that host highly specific symbioses with one or a few types of endosymbionts, other less-abundant members of the microbiota can be easily overlooked. Our work highlights how widespread and specific associations with less-abundant microbes can be. Possibly, these microbes play an important role in the survival and health of their animal hosts.

Biomaterials obtained from probiotic consortia of microorganisms. Potential applications in regenerative medicine

ABSTRACTThe beneficial effects of metabolites resulted from the consortium of probiotic microorganisms are known since the year 220 B.C. when they were used in Asia. The effects of these probiotic consortia were brought into actuality in the last century, after second World War, by researchers of the Moscow Academy of Sciences, during the studies regarding the incidence of cancer in Russia. They have found that at residents of some areas heavily polluted with radiation, the cancer incidence it is practically non-existent. Further investigations revealed that these people were healthy, due to the consumption of a specific mixture, which contains vitamins and minerals (bioproduct), obtained through fermentation, with specific yeasts. Studies have shown that fermented drink contains vitamins from the group B (B1, B2, B3, B5, B6, B7, B9, B12), vitamins A, C, E, polyphenols, amino acids, enzymes, glucuronic acid, usnic acid, caffeine, lactic acid, malonic acid, propionic acid, acetic acid, ethanol (0.5%) and protein (15 g/L). Microbiological analysis of the species involved in the bioprocess showed the existence of the specific symbiosis between several types of microorganisms type: Schizosaccharomyces pombe, Saccharomycodes ludwigii, Brettanomyces bruxellensis, Bacterium xylinum, Bacterium xylinoides Bacterium gluconicum, Bacterium katogenum, Pichia fermentans Bacterium, Acetobacter xylinum Gluconobacter oxydans, Torulaspora, delbueckii. The studies performed in vitro with this bioproduct (mixture), have confirmed that the immunomodulatory effect is due to cultivation media, which contain flavanols and catechins.

The extracellular polysaccharide produced by Enterobacter spp. isolated from root nodules of Abrus precatorius L.

Abstract Extracellular polysaccharide (EPS) of symbiotic bacteria is indispensible for the invasion of root that leads to formation of nodule in legume plant. The chemical structure of the EPS is important for structural recognition at the early stage of infection in highly host specific legume-bacteria symbiosis. Two bacterial strains A3CK and A7CK isolated from the root nodule of legume Abrus precatorius and identified as Enterobacter spp. based on 16S rDNA sequence homology. Both the strains were found to produce copious amount of EPS (88 and 122 µg/ml respectively) in yeast extract mineral medium. The EPS production was increased 485 µg/ml and 656 µg/ml by A3CK and A7CK strain respectively after the medium supplemented with preferable carbon (mannitol), nitrogen (L-asparagine), and vitamin (B12). Gas chromatography coupled with mass spectrometry (GC–MS) analysis of EPS was performed to determine the presence of sugar monomers. GC–MS analysis of alditol-acetate derivatives of acid hydrolyzed EPS of these two strains revealed that presence of sugars such as mannose, glucose and galactose in A3CK strain, whereas glucose and galactose present in A7CK strain. FT-IR spectrum of the EPS indicated the presence of hydroxyl, methyl and carboxylate groups in both the two strains. The possible role of bacterial EPS production in root nodule and their roles in plant – bacteria interaction are briefly discussed.

From mycoheterotrophy to mutualism: mycorrhizal specificity and functioning in Ophioglossum vulgatum sporophytes.

Mycorrhizal functioning in the fern Ophioglossum is complex and poorly understood. It is unknown whether mature O.vulgatum sporophytes form mutualistic associations with fungi of the Glomeromycota and with what specificity. Are green sporophytes able to 'repay' fungal carbon (C) invested in them by mycorrhizal partners during the initially heterotrophic gametophyte and early sporophyte stages of the lifecycle? We identified fungal partners of O.vulgatum sporophytes using molecular techniques and supplied them with (33) P-orthophosphate and O.vulgatum sporophytes with (14) CO2 . We traced the movement of fungal-acquired nutrients and plant-fixed C between symbionts and analysed natural abundance (13) C and (15) N isotope signatures to assess nutritional interactions. We found fungal specificity of O.vulgatum sporophytes towards a mycorrhizal fungus closely related to Glomus macrocarpum. Our radioisotope tracers revealed reciprocal C-for-phosphorus exchange between fern sporophytes and fungal partners, despite competition from surrounding vegetation. Monocultures of O.vulgatum were enriched in (13) C and (15) N, providing inconclusive evidence of mycoheterotrophy when experiencing competition from the surrounding plant community. We show mutualistic and specific symbiosis between a eusporangiate fern and fungi of the Glomeromycota. Our findings suggest a 'take now, pay later' strategy of mycorrhizal functioning through the lifecycle O.vulgatum, from mycoheterotrophic gametophyte to mutualistic aboveground sporophyte.

Biodiversity of the Symbiotic Bacteria Associated with Toxic Marine Dinoflagellate Alexandrium tamarense

Paralytic shellfish poisoning (PSP) toxins are potent neurotoxins mainly produced by dinoflagellates and being concentrated in bivalves through food web transfer. Increasing number of findings of toxin-producing bacteria in the cells of dinoflagellate such as Alexandriumtamarense supports the hypothesis of the bacterial origin of PSP toxins. Evidence that there are specific symbiosis bacterial taxa associated with the phytoplankton indicates the presence of specific selective mechanisms between them, and implies that the symbiosis bacteria have some vital function to the benefit of the dinoflagellates. Studies on the role of toxin-producing symbiosis bacteria in the marine ecosystem are considered to be becoming more important. Although toxigenic bacteria could be isolated from toxic dinoflagellates, it was not clearly proven whether the isolated bacterial strains based on culture-dependent manner and the corresponding intracellular bacteria were the same because of microbial unculturability. This paper aims to demonstrate the biodiversity of the symbiotic bacteria associated with toxic dinoflagellate A. tamarense using the culture-indepen- dent high-throughput pyrosequencing method, as well as the phylogenetic analysis based on 16S rDNA sequences of the symbiotic cultivable bacteria strains isolated from toxic Alexander tamarense.

Biodiversity Study of Intracellular Bacteria Closely Associated with Paralytic Shellfish Poisoning Dinoflagellates Alexandrium tamarense and A. minutum

Paralytic shellfish poisoning (PSP) toxins are potent environmental neurotoxins mainly produced by marien dinoflagellates. Alexandrium spp. are the most abundant and widespread producer of saxitoxin (STX). Currently, the evolutionary history that resulted in the curious cross-kingdom distribution of STX-synthesis remained unclear. However, the increasing number of findings of toxin-producing bacteria in dinoflagellate supports the hypothesis of the bacterial origin of PSP toxins. Addtionally, evidence that there are specific symbiosis bacterial taxa associated with phytoplankton indicates the presence of specific selective mechanisms between them, and implies that the symbiosis bacteria have some vital functions to the benefit of the dinoflagellates. Culture-independent high-throughput pyrosequencing analysis is able to provide a thorough description of microbiota community in environmental samples, which also helps to reveal their potential function. This paper aims to demonstrate the biodiversity of the bacteria closely associated with two toxic dinoflagellate strains, A. tamarense and A. minutum using the pyrosequencing method.

Species specificity of symbiosis and secondary metabolism in ascidians.

Ascidians contain abundant, diverse secondary metabolites, which are thought to serve a defensive role and which have been applied to drug discovery. It is known that bacteria in symbiosis with ascidians produce several of these metabolites, but very little is known about factors governing these 'chemical symbioses'. To examine this phenomenon across a wide geographical and species scale, we performed bacterial and chemical analyses of 32 different ascidians, mostly from the didemnid family from Florida, Southern California and a broad expanse of the tropical Pacific Ocean. Bacterial diversity analysis showed that ascidian microbiomes are highly diverse, and this diversity does not correlate with geographical location or latitude. Within a subset of species, ascidian microbiomes are also stable over time (R=-0.037, P-value=0.499). Ascidian microbiomes and metabolomes contain species-specific and location-specific components. Location-specific bacteria are found in low abundance in the ascidians and mostly represent strains that are widespread. Location-specific metabolites consist largely of lipids, which may reflect differences in water temperature. By contrast, species-specific bacteria are mostly abundant sequenced components of the microbiomes and include secondary metabolite producers as major components. Species-specific chemicals are dominated by secondary metabolites. Together with previous analyses that focused on single ascidian species or symbiont type, these results reveal fundamental properties of secondary metabolic symbiosis. Different ascidian species have established associations with many different bacterial symbionts, including those known to produce toxic chemicals. This implies a strong selection for this property and the independent origin of secondary metabolite-based associations in different ascidian species. The analysis here streamlines the connection of secondary metabolite to producing bacterium, enabling further biological and biotechnological studies.

A review of the effects of soil organisms on plant hormone signalling pathways

Plants interact with a large number of soil organisms. For a long time, these interactions have been the research area of soil ecologists and trophic relationships and physico-chemical modifications of the soil matrix were generally proposed as mechanisms underlying plant-soil organism interactions. However, some specific symbioses and diseases have been well characterized at the molecular level by plant biologists and microbiologists. These interactions involve a physical contact between soil organism and plant. They are mediated through signal molecules that play upon the different plant hormonal signalling pathways, leading to modifications in plant development and defence. Nowadays, the role of signal molecules emerges as an important feature of interactions between plants and free-living soil organisms. In this review we discuss genetic and physiological evidences of hormone signalling involvement in plant response to physically associated but also free-living soil organisms, for very different taxa ranging from the micrometer to the centimetre scales. The same hormone signalling pathways seems to be activated by very different kinds of soil organisms such as bacteria, nematodes, collembola and even earthworms, with common consequences on plant growth, development and defence. Plant hormonal homeostasis appears to be the corner stone to understand and predict the issue of the multiple interactions that plants entertain with the community of soil organisms.

Identification of a dominant gene in Medicago truncatula that restricts nodulation by Sinorhizobium meliloti strain Rm41.

BackgroundLeguminous plants are able to form a root nodule symbiosis with nitrogen-fixing soil bacteria called rhizobia. This symbiotic association shows a high level of specificity. Beyond the specificity for the legume family, individual legume species/genotypes can only interact with certain restricted group of bacterial species or strains. Specificity in this system is regulated by complex signal exchange between the two symbiotic partners and thus multiple genetic mechanisms could be involved in the recognition process. Knowledge of the molecular mechanisms controlling symbiotic specificity could enable genetic improvement of legume nitrogen fixation, and may also reveal the possible mechanisms that restrict root nodule symbiosis in non-legumes.ResultsWe screened a core collection of Medicago truncatula genotypes with several strains of Sinorhizobium meliloti and identified a naturally occurring dominant gene that restricts nodulation by S. meliloti Rm41. We named this gene as Mt-NS1 (for M.truncatulanodulation specificity 1). We have mapped the Mt-NS1 locus within a small genomic region on M. truncatula chromosome 8. The data reported here will facilitate positional cloning of the Mt-NS1 gene.ConclusionsEvolution of symbiosis specificity involves both rhizobial and host genes. From the bacterial side, specificity determinants include Nod factors, surface polysaccharides, and secreted proteins. However, we know relatively less from the host side. We recently demonstrated that a component of this specificity in soybeans is defined by plant NBS-LRR resistance (R) genes that recognize effector proteins delivered by the type III secretion system (T3SS) of the rhizobial symbionts. However, the lack of a T3SS in many sequenced S. meliloti strains raises the question of how the specificity is regulated in the Medicago-Sinorhizobium system beyond Nod-factor perception. Thus, cloning and characterization of Mt-NS1 will add a new dimension to our knowledge about the genetic control of nodulation specificity in the legume-rhizobial symbiosis.

The New Zealand alpine endemic Montigena novae-zelandiae (Fabaceae) shares rhizobial symbionts with Carmichaelia and Clianthus

Thirteen rhizobial strains isolated from New Zealand Carmichaelia spp., Clianthus puniceus, Montigena novae-zelandiae (Montigena) and Sophora spp. and the Australian Swainsona galegifolia in the current or previous studies were tested for their ability to nodulate Montigena. Only rhizobial strains isolated from Carmichaelia spp., and those from Clianthus puniceus that produced functional nodules on their original host, and strains from Montigena produced functional nodules on Montigena. Strains that produced functional nodules on Sophora spp. or Swainsona galegifolia did not nodulate Montigena. Strains that nodulated Montigena, identified here or previously as Mesorhizobium spp., had variable 16S ribosomal RNA, recA and glnII but specific nifH, nodA and nodC genes. Results indicate that Montigena shares rhizobia with its closely related Carmichaelia and Clianthus but not Sophora spp. or Swainsona galegifolia and that the ability of different rhizobial strains to produce functional nodules on Montigena, Carmichaelia and Clianthus puniceus is likely to be dependent on specific symbiosis genes.

A journey into the wild of the cnidarian model system Aiptasia and its symbionts

The existence of coral reef ecosystems relies critically on the mutualistic relationship between calcifying cnidarians and photosynthetic, dinoflagellate endosymbionts in the genus Symbiodinium. Reef-corals have declined globally due to anthropogenic stressors, for example, rising sea-surface temperatures and pollution that often disrupt these symbiotic relationships (known as coral bleaching), exacerbating mass mortality and the spread of disease. This threatens one of the most biodiverse marine ecosystems providing habitats to millions of species and supporting an estimated 500 million people globally (Hoegh-Guldberg et al. 2007). Our understanding of cnidarian–dinoflagellate symbioses has improved notably with the recent application of genomic and transcriptomic tools (e.g. Voolstra et al. 2009; Bayer et al. 2012; Davy et al. 2012), but a model system that allows for easy manipulation in a laboratory environment is needed to decipher underlying cellular mechanisms important to the functioning of these symbioses. To this end, the sea anemone Aiptasia, otherwise known as a ‘pest’ to aquarium hobbyists, is emerging as such a model system (Schoenberg & Trench 1980; Sunagawa et al. 2009; Lehnert et al. 2012). Aiptasia is easy to grow in culture and, in contrast to its stony relatives, can be maintained aposymbiotically (i.e. dinoflagellate free) with regular feeding. However, we lack basic information on the natural distribution and genetic diversity of these anemones and their endosymbiotic dinoflagellates. These data are essential for placing the significance of this model system into an ecological context. In this issue of Molecular Ecology, Thornhill et al. (2013) are the first to present genetic evidence on the global distribution, diversity and population structure of Aiptasia and its associated Symbiodinium spp. By integrating analyses of the host and symbiont, this research concludes that the current Aitpasia taxonomy probably needs revision and that two distinct Aiptasia lineages are prevalent that have probably been spread through human activity. One lineage engages in a specific symbiosis with Symbiodinium minutum throughout the tropics, whereas a second, local Aiptasia sp. population in Florida appears more flexible in partnering with more than one symbiont. The existence of symbiont-specific and symbiont-flexible Aiptasia lineages can greatly complement laboratory-based experiments looking into mechanisms of symbiont selectivity. In a broader context, the study by Thornhill et al. (2013) should inspire more studies to target the natural environment of model systems in a global context targeting all participating member species when establishing ecological and genetic baselines.

Population genetic data of a model symbiotic cnidarian system reveal remarkable symbiotic specificity and vectored introductions across ocean basins

The Aiptasia-Symbiodinium symbiosis is a promising model for experimental studies of cnidarian-dinoflagellate associations, yet relatively little is known regarding the genetic diversity of either symbiotic partner. To address this, we collected Aiptasia from 16 localities throughout the world and examined the genetic diversity of both anemones and their endosymbionts. Based on newly developed SCAR markers, Aiptasia consisted of two genetically distinct populations: one Aiptasia lineage from Florida and a second network of Aiptasia genotypes found at other localities. These populations did not conform to the distributions of described Aiptasia species, suggesting that taxonomic re-evaluation is needed in the light of molecular genetics. Associations with Symbiodinium further demonstrated the distinctions among Aiptasia populations. According to 18S RFLP, ITS2-DGGE and microsatellite flanker region sequencing, Florida anemones engaged in diverse symbioses predominantly with members of Symbiodinium Clades A and B, but also C, whereas anemones from elsewhere harboured only S.minutum within Clade B. Symbiodinium minutum apparently does not form a stable symbiosis with other hosts, which implies a highly specific symbiosis. Fine-scale differences among S.minutum populations were quantified using six microsatellite loci. Populations of S.minutum had low genotypic diversity and high clonality (R=0.14). Furthermore, minimal population structure was observed among regions and ocean basins, due to allele and genotype sharing. The lack of genetic structure and low genotypic diversity suggest recent vectoring of Aiptasia and S.minutum across localities. This first ever molecular-genetic study of a globally distributed cnidarian and its Symbiodinium assemblages reveals host-symbiont specificity and widely distributed populations in an important model system.

Definition and evolution of a new symbiovar, sv. rigiduloides, among Ensifer meliloti efficiently nodulating Medicago species

Understanding functional diversity is one of the main goals of microbial ecology, and definition of new bacterial ecotypes contributes significantly to this objective. Nitrogen-fixing bacteria provide a good system for investigation of ecotypes/biovars/symbiovars, as they present different specific associations with several host plants. This specific symbiosis is reflected both in the nodulation and fixation efficiency and in genetic characters of the bacteria, and several biovars have already been described in the bacterial species Ensifer meliloti. In the present study, the species affiliation of E. meliloti strains trapped from nodules sampled from Medicago rigiduloïdes roots was analyzed using housekeeping recA genes and DNA–DNA hybridization. The genetic diversity of these isolates was also investigated using several symbiotic markers: nodulation (nodA, nodB, nodC) and nitrogen fixation (nifH) genes, as well as the performance of phenotypic tests of nodulation capacity and nitrogen fixation efficiency. These analyses led to the proposal of a new bacterial symbiovar, E. meliloti sv. rigiduloides, that fixed nitrogen efficiently on M. rigiduloïdes, but not on Medicago truncatula. Using phylogenetic reconstructions, including the different described symbiovars, several hypotheses of lateral gene transfer and gene loss are proposed to explain the emergence of symbiovars within this species. The widespread geographical distribution of this symbiovar around the Mediterranean Basin, in contrast to restriction of M. rigiduloïdes to Eastern European countries, suggests that these isolates might also be associated with other plant species. The description of a new symbiovar within E. meliloti confirms the need for accurate bacterial ecological classification, especially for analysis of bacterial populations.

Occurrence of a specific dual symbiosis in the excretory organ of geographically distant Nautiloids populations

Nautilus is one of the most intriguing of all sea creatures, sharing morphological similarities with the extinct forms of coiled cephalopods that evolved since the Cambrian (542-488 mya). Further, bacterial symbioses found in their excretory organ are of particular interest as they provide a great opportunity to investigate the influence of host-microbe interactions upon the origin and evolution of an innovative nitrogen excretory system. To establish the potential of Nautilus excretory organ as a new symbiotic system, it is, however, necessary to assess the specificity of this symbiosis and whether it is consistent within the different species of present-day Nautiloids. By addressing the phylogeny and distribution of bacterial symbionts in three Nautilus populations separated by more than 6000 km (N. pompilius from Philippines and Vanuatu, and N. macromphalus from New Caledonia), this study confirms the specificity of this dual symbiosis involving the presence of betaproteobacteria and spirochaete symbionts on a very wide geographical area. Overall, this work sheds further light on Nautiloids excretory organ as an innovative system of interaction between bacteria and cephalopods.