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 rigiduloides 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. rigiduloides, 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. rigiduloides 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

Purification assay of phosphatases secreted by Hebeloma cylindrosporum and preparation of polyclonal antibodies

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Rhizostabilzation of a mine tailing higly contaminated: Previous study of Cd localization and speciation in Anthyllis vulneraria

The plant Anthyllis vulneraria has been identified in mine tailings and the aim of this study is to determine the mechanisms developed by the plant and its symbiotic association Mesorhizobium metallidurans to tolerate Cd. We particulary intend to determine the distribution and speciation of Cd in plant using a combination of μXRF (X-ray fluorescence) and Cd XANES and μXANES (X-ray Absorption Near Edge Structure)

Degradation of iprodione by a soil Arthrobacter-like strain.

A bacterial strain able to transform iprodione was isolated from a fast iprodione-degrading soil by enrichment procedures. Transformation was detected through 3,5-dichloroaniline production as measured by a rapid colorimetric method. The strain, MA6, was tentatively identified as an Arthrobacter sp. When it was incubated with MA6 in a minimum mineral medium (pH 6.5), iprodione (8.8 mumol/liter) was transformed into two major metabolites that were identified by high-performance liquid chromatography analysis: 3,5-dichlorophenylcarboximide (metabolite 1) and (3,5-dichlorophenylurea) acetic acid (metabolite 2), which was produced after ring cleavage of the former product. These products were synthesized in the laboratory and compared with metabolites 1 and 2 which were formed during iprodione degradation. Small quantities of 3,5-dichloroaniline also appeared in the bacterial culture but did not substantially increase between the first and second days of incubation. In contrast, in the sterile control medium, iprodione was spontaneously transformed into hydantoic acid and an iprodione isomer. Chemical and biological transformations of iprodione seem to occur through two different pathways. One biological degradation pathway is proposed

Soil nitrogen balance resulting from N fixation and rhizodeposition by the symbiotic association Anthyllis vulneraria/Mesorhizobium metallidurans grown in highly polluted Zn, Pb and Cd mine tailings

The association of the legume Anthyllis vulneraria and the grass Festuca arvernensis, was found to be very efficient for the phytostabilisation of highly multi-metal contaminated mine tailings. Our objective was to quantify the contribution of Anthyllis inoculated with its symbiotic bacteria Mesorhizobium metallidurans to the soil N pool and to test whether a starter nitrogen fertilization may improve symbiotic nitrogen fixation and the growth of Festuca. Plants of Festuca and of Anthyllis inoculated with M. metallidurans were grown separately during eight months in pots filled with mine contaminated soil. Estimation of the N fluxes was realized using (15) N isotopic methods. Starter N fertilization (28 kg N ha(-1)) improved symbiotic N-2 fixation and the growth of both species. Belowground N balance (N rhizodeposition - soil N uptake) of the non-fertilized Anthyllis at maturity was negative (-30.6 kg N ha(-1)). However, the amount of N derived from fixation, including above- and belowground parts, was 78.6 kg N ha(-1), demonstrating the ability of this symbiotic association to improve soil N content after senescence. i) soil N enrichment by the N-2-fixing symbiotic association occurs after plant senescence, when decaying leaves and shoots are incorporated into the soil; ii) application of a starter fertilization is an efficient solution to improve phytostabilisation of highly contaminated sites

Molecular and phenotypic characterization of strains nodulating Anthyllis vulneraria in mine tailings, and proposal of Aminobacter anthyllidis sp nov., the first definition of Aminobacter as legume-nodulating bacteria

Bacterial strains from Zn-Pb mine tailings were isolated by trapping with Anthyllis vulneraria, a legume-host suitable for mine substratum phytostabilisation. Sequence analysis of the 16S rRNA gene and three housekeeping genes (atpD, dnaK and recA) showed that they were related to those of the genus Aminobacter. DNA-DNA relatedness of representative isolates supported the placement of novel strains in Aminobacter as a new species. Phenotypic data emphasize their differentiation from the other related species of Aminobacter and Mesorhizobium. Aminobacter isolates exhibited nodA sequences tightly related with M. loti as the closest nodA relative. By contrast, their nodA sequences were highly divergent from those of M. metallidurans, another species associated with A. vulneraria that carries two complete copies of nodA. Therefore, the novel bacterial strains efficient on A. vulneraria represented the first occurrence of legume symbionts in the genus Aminobacter. They represent a new species for which the name Aminobacter anthyllidis sp. nov. is proposed (type strain STM4645(T) = LMG26462(T) = CFBP7437(T))

Zinc accumulation patterns in four Anthyllis vulneraria subspecies supplemented with mineral nitrogen or grown in the presence of their symbiotic bacteria

This work examines Zn accumulation in four Anthyllis vulneraria subspecies supplemented with mineral nitrogen or grown in the presence of their symbiotic bacteria. Anthyllis vulneraria subspecies were grown hydroponically in the presence of high levels of ZnSO4. The plants were either grown in symbiosis with one of two non-metallicolous or metallicolous Mesorhizobium inoculants or in the presence of KNO3. When exposed to 1,000 mu M Zn, shoot and root biomass of three out of our four Anthyllis subspecies cultivated with NO3 dropped significantly by about 24-28 %; carpatica, the fourth subspecies, was not affected. Subspecies carpatica Zn tolerance was confirmed when in symbiosis with the metallicolous strain. In the presence of 1,000 mu M Zn, the different Anthyllis subspecies concentrated more Zn in their roots than in their shoots and only subsp. carpatica accumulated a significant amount of Zn in its shoots. The most remarkable feature was the drastic decrease in Zn concentration in both roots (up to 2.5-3 fold) and shoots (2.6-fold) of subsp. carpatica exposed to 1,000 mu M Zn and nodulated whatever the Mesorhizobium strain used, compared to the N-grown plants. Our results bring new perspectives as regards phytostabilization, with the potential use of a rhizobium-inoculated leguminous subspecies displaying unusual Zn tolerance

Nitrogen-fixing sinorhizobia with Medicago laciniata constitute a novel biovar (bv. medicaginis) of S-meliloti

Sixty-eight new rhizobial isolates were obtained from root-nodules of Medicago laciniata and from Mediterranean soils in Tunisia and France. All of them were identified as Sinorhizobium meliloti on the basis of PCR-RFLP analyses of 16S rDNA and the intergenic spacer sequence between 16S and 23S rDNAs. DNA/DNA hybridization, phenotypic characterization and 16S rRNA gene sequencing led to the conclusion that they belong the same taxon. All new isolates shared the ability to nodulate and fix nitrogen with M. laciniata except 11 of them not capable of fixing nitrogen with this plant and originating from French soils containing no efficiently adapted symbionts with M. laciniata. The nitrogen-fixing rhizobia on M. laciniata differed markedly from the other S. meliloti or Sinorhizobium medicae isolates and references in their symbiotic traits such as nifDK RFLP diversity, nodA sequences and nitrogen effectiveness with tree other different annual Medicago species (M. truncatula, M. polymorpha and M. sauvagei). Two infrasubspecific (biovar) divisions are therefore proposed within S. meliloti: bv. medicaginis for Sinorhizobium efficient on M. laciniata and bv. meliloti for the classically known S. meliloti group represented by the strains ATCC9930(T) and RCR 2011 efficient on M. sativa

Mediterranean land surfaces under global change : towards a roadmap for sustainable land use in Europe

Abandoned mines are a recurrent problem for nearby communities in Mediterranean regions because mine tailings represent a major source of polymetallic contamination. Metal contaminants are emitted in mining areas and dispersed by wind and water erosion in the surroundings. The goal of this literature review was to identify the specific features of polymetallic contamination arising from abandoned mines in the Mediterranean regions. Mediterranean climate conditions and local geochemical context are the most important factors that control the metal-bearing particle dispersion toward the different compartments of ecosystems. Acid mine drainage, as an important source of damage to the environment, is limited to a certain extent by the predominance of carbonate rocks in the Mediterranean regions. In opposite, aeolian contamination is specific to the semiarid conditions of the Mediterranean climate. In this context, impacts on different compartments such as agricultural soils and edible plants or human populations were underlined. The analysis of environmental laws and regulations of North and South Mediterranean countries shows that one of the main differences is the lack of identification and definition of mining waste as a public concern in the latter countries. In order to limit the transfer of contaminants from mining waste to the different components of the environment, phytostabilization of mine tailings was considered as the more adapted green technology even in the Mediterranean region where water access is limited. Finally, this review of polymetallic pollution from abandoned mines in Mediterranean regions enabled to identify priority actions for future research