From spontaneous to inoculant symbiotic nodulation of legume trees: the example of Acacia mangium

Acacia mangium is a legume tree native of Australasia. Tt has been introduced in many tropical countries especially in the context of industrial plantations. Tt has the exceptional capacity to establish symbioses with three types of microorganisms: nitrogen-fixing bacteria, arbuscular and ecto-mycorrhizal fungi, enabling a great productivity and adaptability. In this context, many field trials were established to test the effects of controlled inoculation with selected symbiotic bacteria versus natural colonization with indigenous strains. In introduction areas, A. mangium spontaneously nodulate with local and often ineffective bacteria. When inoculated, the persistence of inoculants, their impact on local biodiversity and possible genetic recombination with local strains have to be explored. The aim ofthis study was to describe the genetic diversity ofbacteria spontaneously nodulating A. mangium in Brazil and to evaluate, by molecular tracing, the durability ofselected strains used as inoculants. Three different sites, several hundred kilometres distant, were studied, each with inoculated and non inoculated plots. About one hundred strains were isolated and sequenced on three housekeeping (g/nB, dnaK and recA) and one symbiotic (nodA) genes. We showed that, whatever the site and the treatment, A. mangium is nodulated by bacteria of the genera Bradyrhizobium and Mesorhizobium. We observed a significant genetic differentiation not only among the three sites, but also between inoculated and non-inoculated plots in each site. The two inoculated strains were never detected, even few months after inoculation, be they in nursery or in plantation, raising the question ofthe usefulness of such artificial inoculation. At last, Mesorhizobium strains, display a genetic diversity within the housekeeping genes, shared exactly the same symbiotic sequence gene, opening the door to the possible transfer of the symbiotic island from unknown symbiotic strain. (Texte integral

Effective arbuscular mycorrhizal fungi in the roots of Tetraclinis articulata and Lavandula multifida in Moroccan Tetraclinis woodlands

The diversity of arbuscular mycorrhizal fungi (AMF) in roots of two plant species (arar, Tetraclinis articulata and lavender, Lavandula multifida) that exist alone or co-occur in Moroccan Tetraclinis woodlands was characterized using molecular techniques. The interaction between the two plant species on their root AMF communities was also studied. We analysed the large subunit (LSU) ribosomal RNA gene amplified by nested PCR from a root DNA extract using AM fungal-specific primers. A total of 200 cloned fragments from five root bulk samples of the two plant species were analysed by restriction fragment length polymorphism (RFLP) and 30 of them were sequenced. Phylogenetic analyses demonstrated that these RFLP types correspond to eight phylotypes: five belonged to the Gigasporaceae and three to the Glomeraceae. The highest diversity was found in the roots of T. articulata alone, followed by the association T. articulata/L. multifida and, finally, L. multifida alone. Many AMF were shared between the two species, although a few of them had a preference for one or the other. In addition, PCA analysis showed clearly that the AMF community colonizing T. articulata differed significantly from that colonizing L. multifida. Our results reveal an impact of plant interactions on the AMF community. (Résumé d'auteur

Evolution Spatio-Temporelle des populations de Bradyrhizobium associées à Acacia mangium

En 1966, l'aire de répartition d'Acacia mangium était encore restreinte à quelques ilots dans le Northern Queensland Australien et la Papouasie Nouvelle Guinée. En 2010, cette espèce représente un quart des surfaces sylvicoles plantées au monde, en proportion similaire au teck, avec plus de 2 millions d'Ha cultivés. A. mangium est une légumineuse s'associant à des bactéries du genre Bradyrhizobium. Dans le cadre d'une étude de diversité, des graines et des nodules (et les bactéries symbiotiques se cachant à l'intérieur..) avaient été récoltés en 1986 dans plusieurs sites australiens. En 2007 et 2009, sur approximativement les mêmes sites, nous avons procédé à de nouveaux échantillonnages et isolements bactériens. De plus, A. mangium ayant été introduit notamment en Malaisie et au Brésil, nous avons caractérisé les symbiotes spontanément retrouvés dans les plantations non inoculées artificiellement. Nous obtenons ainsi une image de l'évolution de la diversité des bactéries symbiotiques s'associant avec A. mangium au niveau temporel mais aussi spatiale. Nos résultats montrent que sur 20 ans, plusieurs allèles recA et nodA se retrouvent, avec un niveau de recouvrement plus élevé pour les prélèvements situés à deux ans d'intervalle. De plus, un haplotype multilocus est retrouvé à 20 ans d'intervalle, suggérant une très faible évolution des populations bactériennes, malgré des indices de recombinaison évidents. La similitude des fréquences sur deux ans renforce cette image de forte stabilité des populations. Inversement, la dispersion des isolats et des gènes apparait extrêmement limitée, avec une absence totale d'haplotype commun avec le Brésil, et deux entre la Malaisie et le Brésil. Les gènes de ménage et symbiotiques ne présentent cependant pas les mêmes patrons de diversification, le Brésil possédant une diversité symbiotique propre par rapport aux autres sites. Une possible histoire globale des Bradyrhizobium peut alors être proposée pour comprendre comment ce genre a évolué et évoluera encore. (Résumé d'auteur

The Unique Lipidomic Signatures of Saccharina latissima Can Be Used to Pinpoint Their Geographic Origin

The aquaculture of macroalgae for human consumption and other high-end applications is experiencing unprecedented development in European countries, with the brown algae Saccharina latissima being the flag species. However, environmental conditions in open sea culture sites are often unique, which may impact the biochemical composition of cultured macroalgae. The present study compared the elemental compositions (CHNS), fatty acid profiles, and lipidomes of S. latissima originating from three distinct locations (France, Norway, and the United Kingdom). Significant differences were found in the elemental composition, with Norwegian samples displaying twice the lipid content of the others, and significantly less protein (2.6%, while French and UK samples contained 6.3% and 9.1%, respectively). The fatty acid profiles also differed considerably, with UK samples displaying a lower content of n-3 fatty acids (21.6%), resulting in a higher n-6/n-3 ratio. Regarding the lipidomic profile, samples from France were enriched in lyso lipids, while those from Norway displayed a particular signature of phosphatidylglycerol, phosphatidylinositol, and phosphatidylcholine. Samples from the UK featured higher levels of phosphatidylethanolamine and, in general, a lower content of galactolipids. These differences highlight the influence of site-specific environmental conditions in the shaping of macroalgae biochemical phenotypes and nutritional value. It is also important to highlight that differences recorded in the lipidome of S. latissima make it possible to pinpoint specific lipid species that are likely to represent origin biomarkers. This finding is relevant for future applications in the field of geographic origin traceability and food controlpublishedVersio

Geographical and temporal variations of the diversity of symbiotic bacteria associated with Acacia mangium : area of origin, area of introduction and controlled inoculation

Acacia mangium Willd. est une légumineuse ligneuse introduite dans de nombreux pays tropicaux à partir de son aire d'origine (Australie), avec ou sans inoculations volontaires par des rhizobiums sélectionnés. Des campagnes d'échantillonnage des bactéries symbiotiques fixatrices d'azote ont été réalisées dans sa zone d'origine à différentes époques (1986, 2007 et 2009) et dans trois zones d'introduction (Brésil, Sénégal et Malaisie). Après isolement et test de nodulation homologue, la diversité de plus de 500 souches a été analysée sur un gène de ménage (recA) et un gène symbiotique (nodA). Nous avons confirmé qu'A. mangium était essentiellement nodulé par des Bradyrhizobium. La comparaison des communautés symbiotiques issues de la zone d'origine et des zones d'introduction montre une importante diversité dans la région d'origine et une diversité plus réduite dans les zones d'introduction. En Australie, quelques génotypes sont majoritaires et persistent durant 20 ans. Une structuration phylogéographique et un isolement par la distance à une échelle mondiale ont été mis en évidence pour le gène symbiotique nodA. Enfin, lorsque A. mangium a été introduit conjointement avec une souche sélectionnée, le devenir de cet inoculum est variable en fonction des essais d'introduction. De plus, nous mettons en évidence des phénomènes de transfert du gène symbiotique nodA entre une souche introduite et les bactéries autochtones. Les résultats acquis nous permettent d'émettre des recommandations en termes de sauvegarde de la biodiversité microbienne symbiotique en zone naturelle, et sur la pertinence de procéder à des inoculations lors de la mise en place de plantations d'A. mangium.From Australia, its native area and since three decades, the legume tree Acacia mangium Willd. has been introduced in many tropical countries, sometimes with selected rhizobium strains. A. mangium symbiotic nodule bacteria have been sampled in Australia at different times (1986, 2007, 2009), as well as in countries where it was introduced for inoculation trials (Brazil, Senegal and Malaysia). More than 500 isolates were obtained and checked for homologous nodulation. They were then characterized on the housekeeping recA and symbiotic nodA genes. We demonstrated through this study that A. mangium was almost always nodulated by Bradyrhizobium. Phylogenies of the obtained sequences were made, showing a high level of bacterial diversity in the native area, and a much more reduced diversity in introduced areas. In Australia, some genotypes were predominant and persist over 20 years. A phylogeographic structuration and isolation by distance at a global scale were demonstrated for the nodA symbiotic gene. Among introduced areas, the main result was the unsystematic occurrence of inoculated strains. We highlighted horizontal nodA symbiotic gene transfer between inoculated and indigenous bacterial strains. These data allow to make recommendations in terms of microbial diversity conservation in natural areas and on the need for inoculation of A. mangium in forestry practices

Recent mobility of plastid encoded group II introns and twintrons in five strains of the unicellular red alga <i>Porphyridium</i>

Group II introns are closely linked to eukaryote evolution because nuclear spliceosomal introns and the small RNAs associated with the spliceosome are thought to trace their ancient origins to these mobile elements. Therefore, elucidating how group II introns move, and how they lose mobility can potentially shed light on fundamental aspects of eukaryote biology. To this end, we studied five strains of the unicellular red alga Porphyridium purpureum that surprisingly contain 42 group II introns in their plastid genomes. We focused on a subset of these introns that encode mobility-conferring intron-encoded proteins (IEPs) and found them to be distributed among the strains in a lineage-specific manner. The reverse transcriptase and maturase domains were present in all lineages but the DNA endonuclease domain was deleted in vertically inherited introns, demonstrating a key step in the loss of mobility. P. purpureum plastid intron RNAs had a classic group IIB secondary structure despite variability in the DIII and DVI domains. We report for the first time the presence of twintrons (introns-within-introns, derived from the same mobile element) in Rhodophyta. The P. purpureum IEPs and their mobile introns provide a valuable model for the study of mobile retroelements in eukaryotes and offer promise for biotechnological applications.</jats:p

Recent mobility of plastid encoded group II introns and twintrons in five strains of the unicellular red alga Porphyridium

Group II introns are closely linked to eukaryote evolution because nuclear spliceosomal introns and the small RNAs associated with the spliceosome are thought to trace their ancient origins to these mobile elements. Therefore, elucidating how group II introns move, and how they lose mobility can potentially shed light on fundamental aspects of eukaryote biology. To this end, we studied five strains of the unicellular red alga Porphyridium purpureum that surprisingly contain 42 group II introns in their plastid genomes. We focused on a subset of these introns that encode mobility-conferring intron-encoded proteins (IEPs) and found them to be distributed among the strains in a lineage-specific manner. The reverse transcriptase and maturase domains were present in all lineages but the DNA endonuclease domain was deleted in vertically inherited introns, demonstrating a key step in the loss of mobility. P. purpureum plastid intron RNAs had a classic group IIB secondary structure despite variability in the DIII and DVI domains. We report for the first time the presence of twintrons (introns-within-introns, derived from the same mobile element) in Rhodophyta. The P. purpureum IEPs and their mobile introns provide a valuable model for the study of mobile retroelements in eukaryotes and offer promise for biotechnological applications

Effects of Medicago truncatula Genetic Diversity, Rhizobial Competition, and Strain Effectiveness on the Diversity of a Natural Sinorhizobium Species Community▿

We investigated the genetic diversity and symbiotic efficiency of 223 Sinorhizobium sp. isolates sampled from a single Mediterranean soil and trapped with four Medicago truncatula lines. DNA molecular polymorphism was estimated by capillary electrophoresis-single-stranded conformation polymorphism and restriction fragment length polymorphism on five loci (IGSNOD, typA, virB11, avhB11, and the 16S rRNA gene). More than 90% of the rhizobia isolated belonged to the Sinorhizobium medicae species (others belonged to Sinorhizobium meliloti), with different proportions of the two species among the four M. truncatula lines. The S. meliloti population was more diverse than that of S. medicae, and significant genetic differentiation among bacterial populations was detected. Single inoculations performed in tubes with each bacterial genotype and each plant line showed significant bacterium-plant line interactions for nodulation and N2 fixation levels. Competition experiments within each species highlighted either strong or weak competition among genotypes within S. medicae and S. meliloti, respectively. Interspecies competition experiments showed S. meliloti to be more competitive than S. medicae for nodulation. Although not highly divergent at a nucleotide level, isolates collected from this single soil sample displayed wide polymorphism for both nodulation and N2 fixation. Each M. truncatula line might influence Sinorhizobium soil population diversity differently via its symbiotic preferences. Our data suggested that the two species did not evolve similarly, with S. meliloti showing polymorphism and variable selective pressures and S. medicae showing traces of a recent demographic expansion. Strain effectiveness might have played a role in the species and genotype proportions, but in conjunction with strain adaptation to environmental factors