Publications by authors named "Salem Djedidi"

18 Publications

  • Page 1 of 1

Influence of potassium-solubilizing bacteria on the growth and radiocesium phyto-transfer of Brassica rapa L. var. perviridis grown in contaminated Fukushima soils.

J Environ Radioact 2021 Oct 17;237:106682. Epub 2021 Jun 17.

Institute of Agriculture, Tokyo University of Agriculture and Technology, Saiwaicho 3-5-8, Fuchu, Tokyo, 183-12 8509, Japan; The Faculty of Food and Agricultural Science, Fukushima University, Kanayagawa, Fukushima City, Fukushima, 960-1296, Japan.

The supply of K, being the chemical analog of Cs, affects the phytotransfer of radiocesium such as Cs from contaminated soils and its accumulation in plant tissues. Since K and Cs have high affinity to the same clay particle surfaces, the presence of potassium-solubilizing bacteria (KSB) could increase the availability of not only K in the rhizosphere but also of radiocesium. In this study, we obtained five KSB isolates with the highest solubilization capacities from soybean rhizosphere on modified Aleksandrov medium containing sericite as K source. Based on biochemical and 16S rRNA gene sequence analysis, we identified the bacteria as Bacillus aryabhattai MG774424, Pseudomonas umsongensis MG774425, P. frederiksbergensis MG774426, Burkholderia sabiae MG774427, and P. mandelii MG774428. We evaluated the KSB isolates based on plant growth promotion and Cs accumulation in komatsuna (Brassica rapa L. var. Perviridis) grown in three soils collected from Miyanoiri, Takanishi, and Ota contaminated by Cs from the Fukushima accident. Inoculation with KSB showed beneficial effects on plant growth and increased the overall plant biomass production (~40%). On the average, KSB inoculation resulted in the removal of 0.07 ± 0.04% of Cs from the soil, more than twice the control. But similar to the effect of KSB inoculation on komatsuna biomass production, different KSBs performed variably and exhibited site-specific responses independent of their K-solubilizing capacities, with higher Cs phyto-transfer in roots than in shoots. In terms of root transfer factor (TF), values were highest in komatsuna plants grown in Miyanoiri and Ota soils inoculated with P. frederiksbergensis and Burkholderia sabiae, while they were highest in Takanishi soils inoculated with Bacillus aryabhattai and P. umsongensis. These TF values were also much higher than previously reported values for komatsuna grown in Cs-contaminated Fukushima soils inoculated with other rhizobacteria. Thus, KSB inoculation significantly enhance not only the growth of komatsuna but Cs uptake.
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http://dx.doi.org/10.1016/j.jenvrad.2021.106682DOI Listing
October 2021

Characterization of Rhizobia for the Improvement of Soybean Cultivation at Cold Conditions in Central Europe.

Microbes Environ 2020 ;35(1)

Institute of Global Innovation Research (GIR), Tokyo University of Agriculture and Technology.

In central Europe, soybean cultivation is gaining increasing importance to reduce protein imports from overseas and make cropping systems more sustainable. In the field, despite the inoculation of soybean with commercial rhizobia, its nodulation is low. In many parts of Europe, limited information is currently available on the genetic diversity of rhizobia and, thus, biological resources for selecting high nitrogen-fixing rhizobia are inadequate. These resources are urgently needed to improve soybean production in central Europe. The objective of the present study was to identify strains that have the potential to increase nitrogen fixation by and the yield of soybean in German soils. We isolated and characterized 77 soybean rhizobia from 18 different sampling sites. Based on a multilocus sequence analysis (MLSA), 71% of isolates were identified as Bradyrhizobium and 29% as Rhizobium. A comparative analysis of the nodD and nifH genes showed no significant differences, which indicated that the soybean rhizobia symbiotic genes in the present study belong to only one type. One isolate, GMF14 which was tolerant of a low temperature (4°C), exhibited higher nitrogen fixation in root nodules and a greater plant biomass than USDA 110 under cold conditions. These results strongly suggest that some indigenous rhizobia enhance biological nitrogen fixation and soybean yield due to their adaption to local conditions.
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http://dx.doi.org/10.1264/jsme2.ME19124DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7104276PMC
March 2020

Isolation and Screening of Indigenous Plant Growth-promoting Rhizobacteria from Different Rice Cultivars in Afghanistan Soils.

Microbes Environ 2019 Dec 14;34(4):347-355. Epub 2019 Sep 14.

Institute of Agriculture, Tokyo University of Agriculture and Technology.

To develop biofertilizers for rice in Afghanistan, 98 plant growth-promoting rhizobacteria were isolated from rice plants and their morphological and physiological characteristics, such as indole-3-acetic acid production, acetylene reduction, phosphate and potassium solubilization, and siderophore production, were evaluated. The genetic diversity of these bacteria was also analyzed based on 16S rRNA gene sequences. Of 98 bacteria, 89.7% produced IAA, 54.0% exhibited nitrogenase activity, and 40% showed phosphate solubilization and siderophore production. Some isolates assigned to Pseudomonas (brassicacearum, chengduensis, plecoglossicida, resinovorans, and straminea) formed a relationship with rice, and P. resinovorans and P. straminea showed nitrogen fixation. Rhizobium borbori and R. rosettiformans showed a relationship with rice plants and nitrogen fixation. Among the isolates examined, AF134 and AF137 belonging to Enterobacter ludwigii and P. putida produced large amounts of IAA (92.3 μg mL) and exhibited high nitrogenase activity (647.4 nmol CH h), respectively. In the plant growth test, more than 70% of the inoculated isolates showed significantly increased root and shoot dry weights. Highly diverse bacterial isolates showing promising rice growth-promoting traits were obtained from Afghanistan alkaline soils.
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http://dx.doi.org/10.1264/jsme2.ME18168DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6934389PMC
December 2019

Complete Genome Sequence of Plant Growth-Promoting Bacillus pumilus TUAT1.

Microbiol Resour Announc 2019 May 23;8(21). Epub 2019 May 23.

Institute of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan

TUAT1 was isolated from soil in a university research field. Strain TUAT1 has the ability to promote the growth of plants, including that of rice, and has been commercialized as a biofertilizer. Here, we sequenced and annotated the genome of TUAT1 to understand the molecular mechanisms underlying its plant growth promotion.
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http://dx.doi.org/10.1128/MRA.00076-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6533381PMC
May 2019

Evaluation of Immune Responses Induced by Simultaneous Inoculations of Soybean (Glycine max [L.] Merr.) with Soil Bacteria and Rhizobia.

Microbes Environ 2019 Mar 5;34(1):64-75. Epub 2019 Feb 5.

Institute of Agriculture, TUAT.

Legumes form root nodules and fix atmospheric nitrogen by establishing symbiosis with rhizobia. However, excessive root nodules are harmful to plants because of the resulting overconsumption of energy from photosynthates. The delay of an inoculation of the soybean super-nodulation mutant NOD1-3 with Bradyrhizobium diazoefficiens USDA110 by 5 d after an inoculation with several soil bacteria confirmed that one bacterial group significantly decreased root nodules throughout the study period. Moreover, no significant changes were observed in nitrogen fixation by root nodules between an inoculation with USDA 110 only and co-inoculation treatments. To clarify the potential involvement of PR proteins in the restriction of nodule formation in the plants tested, the relative expression levels of PR-1, PR-2, PR-5, and PDF1.2 in NOD1-3 roots were measured using real-time PCR. One group of soil bacteria (Gr.3), which markedly reduced nodule numbers, significantly induced the expression of PR-1, PR-5 and PDF1.2 genes by day 5 after the inoculation. By days 7, 10, and 20 after the inoculation, the expression levels of PR-2 and PR-5 were lower than those with the uninoculated treatment. Inoculations with this group of soil bacteria resulted in lower root nodule numbers than with other tested soil bacteria exerting weak inhibitory effects on nodulation, and were accompanied by the induction of plant defense-related genes. Thus, PR genes appear to play important roles in the mechanisms that suppresses nodule formation on soybean roots.
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http://dx.doi.org/10.1264/jsme2.ME18110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6440728PMC
March 2019

Transfer of radiocesium from rhizosphere soil to four cruciferous vegetables in association with a Bacillus pumilus strain and root exudation.

J Environ Radioact 2016 Nov 10;164:209-219. Epub 2016 Aug 10.

Leibniz Centre for Agricultural Landscape Research, Institute of Land Use Systems, Eberswalder Str. 84, 15374 Muencheberg, Germany. Electronic address:

This study was carried out to assess the effect of Bacillus pumilus on the roots of four cruciferous vegetables with different root structures in regard to enhancement of Cs bioavailability in contaminated rhizosphere soil. Results revealed that B. pumilus inoculation did not enhance the plant biomass of vegetables, although it increased root volume and root surface areas of all vegetables except turnip. The pH changes due to rhizosphere acidification by B. pumilus inoculation and root exudation did not affect the bioavailability of Cs. However, concentrations of Cs in plant tissues and soil-to-plant transfer values increased as a result of the larger root volume and root surface area of vegetables due to inoculation. Moreover, leafy vegetables, which possessed larger root volume and root surface areas, had a higher Cs transfer value than root vegetables.
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http://dx.doi.org/10.1016/j.jenvrad.2016.07.006DOI Listing
November 2016

Genotypic difference in (137)Cs accumulation and transfer from the contaminated field in Fukushima to azuki bean (Vigna angularis).

J Environ Radioact 2016 Jul 19;158-159:138-47. Epub 2016 Apr 19.

Instutute of Agriculture, Tokyo University of Agriculture and Technology, Saiwaicho 3-5-8, Fuchu, Tokyo, 183-8509, Japan. Electronic address:

The screening of mini-core collection of azuki bean accessions (Vigna angularis (Willd.) Ohwi & Ohashi) for comparative uptake of (137)Cs in their edible portions was done in field trials on land contaminated by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Ninety seven azuki bean accessions including their wild relatives from a Japanese gene bank, were grown in a field in the Fukushima prefecture, which is located approximately 51 km north of FDNPP. The contamination level of the soil was 3665 ± 480 Bq kg(-1) dry weight ((137)Cs, average ± SD). The soil type comprised clay loam, where the sand: silt: clay proportion was 42:21:37. There was a significant varietal difference in the biomass production, radiocaesium accumulation and transfer factor (TF) of radiocaesium from the soil to edible portion. Under identical agricultural practice, the extent of (137)Cs accumulation by seeds differed between the accessions by as much as 10-fold. Inter-varietal variation was expressed at the ratio of the maximum to minimum observed (137)Cs transfer factor for seeds ranged from 0.092 to 0.009. The total biomass, time to flowering and maturity, and seed yield had negative relationship to (137)Cs activity concentration in seeds. The results suggest that certain variety/varieties of azuki bean which accumulated less (137)Cs in edible portion with preferable agronomic traits are suitable to reduce the (137)Cs accumulation in food chain on contaminated land.
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http://dx.doi.org/10.1016/j.jenvrad.2016.04.011DOI Listing
July 2016

Growth and (137)Cs uptake and accumulation among 56 Japanese cultivars of Brassica rapa, Brassica juncea and Brassica napus grown in a contaminated field in Fukushima: Effect of inoculation with a Bacillus pumilus strain.

J Environ Radioact 2016 Jun 14;157:27-37. Epub 2016 Mar 14.

Institute of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan. Electronic address:

Fifty six local Japanese cultivars of Brassica rapa (40 cultivars), Brassica juncea (10 cultivars) and Brassica napus (6 cultivars) were assessed for variability in growth and (137)Cs uptake and accumulation in association with a Bacillus pumilus strain. Field trial was conducted at a contaminated farmland in Nihonmatsu city, in Fukushima prefecture. Inoculation resulted in different responses of the cultivars in terms of growth and radiocesium uptake and accumulation. B. pumilus induced a significant increase in shoot dry weight in 12 cultivars that reached up to 40% in one B. rapa and three B. juncea cultivars. Differences in radiocesium uptake were observed between the cultivars of each Brassica species. Generally, inoculation resulted in a significant increase in (137)Cs uptake in 22 cultivars, while in seven cultivars it was significantly decreased. Regardless of plant cultivar and bacterial inoculation, the transfer of (137)Cs to the plant shoots (TF) varied by a factor of up to 5 and it ranged from to 0.011 to 0.054. Five inoculated cultivars, showed enhanced shoot dry weights and decreased (137)Cs accumulations, among which two B. rapa cultivars named Bitamina and Nozawana had a significantly decreased (137)Cs accumulation in their shoots. Such cultivars could be utilized to minimize the entry of radiocesium into the food chain; however, verifying the consistency of their radiocesium accumulation in other soils is strongly required. Moreover, the variations in growth and radiocesium accumulation, as influenced by Bacillus inoculation, could help selecting well grown inoculated Brassica cultivars with low radiocesium accumulation in their shoots.
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http://dx.doi.org/10.1016/j.jenvrad.2016.02.024DOI Listing
June 2016

Relations of fine-root morphology on (137)Cs uptake by fourteen Brassica species.

J Environ Radioact 2015 Dec 7;150:203-12. Epub 2015 Sep 7.

Leibniz Centre for Agricultural Landscape Research, Institute of Land Use Systems, Eberswalder str. 84, 15374, Muencheberg, Germany. Electronic address:

Fourteen Brassica species consisting of seven leafy vegetables and seven root vegetables were examined for (137)Cs uptake differences in relation to their fine-root morphological characters. A pot experiment was conducted from November 2014 to February 2015 in a Phytroton using a contaminated soil of Fukushima prefecture. Leafy vegetables showed bigger root diameters, larger root surface area and larger root volume. Consequently, leafy vegetables had higher (137)Cs uptake compared to root vegetables. Among the three fine-root parameters, only root surface area was observed as a significant contributing factor to higher (137)Cs uptake in terms of transfer factor (TF, dry weight basis). Kakina exhibited higher (137)Cs TF value (0.20) followed by Chinese cabbage (0.18) and mizuna (0.17). Lower TF values were observed in turnip (0.059), rutabaga (Kitanoshou) (0.062) and radish (Ha daikon) (0.064).
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http://dx.doi.org/10.1016/j.jenvrad.2015.08.023DOI Listing
December 2015

Growth and (137)Cs uptake of four Brassica species influenced by inoculation with a plant growth-promoting rhizobacterium Bacillus pumilus in three contaminated farmlands in Fukushima prefecture, Japan.

Sci Total Environ 2015 Jul 2;521-522:261-9. Epub 2015 Apr 2.

Institute of Agriculture, Tokyo University of Agriculture and Technology, Saiwaicho 3-5-8, Fuchu, Tokyo 183-8509, Japan. Electronic address:

The effectiveness of the plant growth-promoting rhizobacterium Bacillus pumilus regarding growth promotion and radiocesium ((137)Cs) uptake was evaluated in four Brassica species grown on different (137)Cs contaminated farmlands at Fukushima prefecture in Japan from June to August 2012. B. pumilus inoculation did not enhance growth in any of the plants, although it resulted in a significant increase of (137)Cs concentration and higher (137)Cs transfer from the soil to plants. The Brassica species exhibited different (137)Cs uptake abilities in the order Komatsuna>turnip>mustard>radish. TF values of (137)Cs ranged from 0.018 to 0.069 for all vegetables. Komatsuna possessed the largest root surface area and root volume, and showed a higher (137)Cs concentration in plant tissue and higher (137)Cs TF values (0.060) than the other vegetables. Higher (137)Cs transfer to plants was prominent in soil with a high amount of organic matter and an Al-vermiculite clay mineral type.
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http://dx.doi.org/10.1016/j.scitotenv.2015.03.109DOI Listing
July 2015

Transfer of radiocesium to four cruciferous vegetables as influenced by organic amendment under different field conditions in Fukushima Prefecture.

J Environ Radioact 2015 Feb 5;140:148-55. Epub 2014 Dec 5.

Institute of Agriculture, Tokyo University of Agriculture and Technology, Saiwaicho 3-5-8, Fuchu, Tokyo 183-8509, Japan. Electronic address:

Soil-to-plant transfer of radiocesium ((137)Cs) in four cruciferous vegetables as influenced by cattle manure-based compost amendment was investigated. Komatsuna, mustard, radish and turnip were cultivated in three different (137)Cs-contaminated fields at Nihonmatsu City in Fukushima Prefecture from June to August 2012. Results revealed that organic compost amendments stimulated plant biomass production and tended to induce higher (137)Cs concentration in the cruciferous vegetables in most cases. Among the studied sites, Takanishi soil possessing low exchangeable potassium (0.10 cmolc kg(-1)) was associated with an increased concentration of (137)Cs in plants. Radiocesium transfer factor (TF) values of the vegetables ranged from 0.025 to 0.119. The increase in (137)Cs TFs was dependent on larger plant biomass production, high organic matter content, and high sand content in the studied soils. Average (137)Cs TF values for all study sites and compost treatments were higher in Komatsuna (0.072) and radish (0.059), which exhibited a higher biomass production compared to mustard and turnip. The transferability of (137)Cs to vegetables from soils was in the order Komatsuna > radish > mustard > turnip. The highest (137)Cs TF value (0.071) of all vegetables was recorded for a field where the soil had high organic matter content and a high clay proportion of 470 g kg(-1) consisting of Al-vermiculite clay mineral.
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http://dx.doi.org/10.1016/j.jenvrad.2014.11.015DOI Listing
February 2015

Evaluation of the possibility to use the plant-microbe interaction to stimulate radioactive 137Cs accumulation by plants in a contaminated farm field in Fukushima, Japan.

J Plant Res 2015 Jan 15;128(1):147-59. Epub 2014 Nov 15.

Department of Biological Production Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-chou, Fuchu, Tokyo, 183-8509, Japan.

Field experiments in a contaminated farmland in Nihonmatsu city, Fukushima were conducted to assess the effectiveness of the plant-microbe interaction on removal of radiocesium. Before plowing, 93.3% of radiocesium was found in the top 5 cm layer (5,718 Bq kg DW(-1)). After plowing, Cs radioactivity in the 0-15 cm layer ranged from 2,037 to 3,277 Bq kg DW(-1). Based on sequential extraction, the percentage of available radiocesium (water soluble + exchangeable) was fewer than 10% of the total radioactive Cs. The transfer of (137)Cs was investigated in three agricultural crops; komatsuna (four cultivars), Indian mustard and buckwheat, inoculated with a Bacillus or an Azospirillum strains. Except for komatsuna Nikko and Indian mustard, inoculation with both strains resulted in an increase of biomass production by the tested plants. The highest (137)Cs radioactivity concentration in above-ground parts was found in Bacillus-inoculated komatsuna Nikko (121 Bq kg DW(-1)), accompanied with the highest (137)Cs TF (0.092). Furthermore, komatsuna Nikko-Bacillus and Indian mustard-Azospirillum associations gave the highest (137)Cs removal, 131.5 and 113.8 Bq m(-2), respectively. Despite the beneficial effect of inoculation, concentrations of (137)Cs and its transfer to the tested plants were not very high; consequently, removal of (137)Cs from soil would be very slow.
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http://dx.doi.org/10.1007/s10265-014-0678-3DOI Listing
January 2015

Stable cesium uptake and accumulation capacities of five plant species as influenced by bacterial inoculation and cesium distribution in the soil.

J Plant Res 2014 Sep 8;127(5):585-97. Epub 2014 Jul 8.

Department of Biological Production Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-chou, Fuchu, Tokyo, 183-8509, Japan.

The effects of inoculation with Bacillus and Azospirillum strains on growth and cesium accumulation of five plant species, Komatsuna, Amaranth, sorghum, common millet and buckwheat, grown on cesium-spiked soil were assessed for potential use in cesium remediation. Pot experiments were performed using "artificially" Cs-contaminated soil. Three treatments were applied based on Cs location in the soil. For a soil height of 15 cm in the pots, Cs was added as follows: in the top five cm to imitate no ploughing condition; in the bottom five cm simulating inverted ploughing; and uniformly distributed Cs reproducing normal plowing. Generally, inoculation of Cs-exposed plants significantly enhanced growth and tolerance to this element. Transfer factor (ratio of Cs concentration in the plant tissues to that in surrounding soil) was strongly influenced by Cs distribution, with higher values in the top-Cs treatment. Within this treatment, inoculation of Komatsuna with Bacillus and Azospirillum strains resulted in the greatest transfer factors of 6.55 and 6.68, respectively. Cesium content in the shoots was high in the Azospirillum-inoculated Komatsuna, Amaranth, and buckwheat, i.e., 1,830, 1,220, and 1,030 µg per pot, respectively (five plants were grown in each pot). Therefore, inoculation of Komatsuna and Amaranth with the strains tested here could be effective in enhancing Cs accumulation. The decrease of Cs transfer under uniform- and bottom-Cs treatments would suggest that countermeasures aiming at decreasing the transfer of Cs could rely on ploughing practices.
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http://dx.doi.org/10.1007/s10265-014-0647-xDOI Listing
September 2014

Phylogenetic diversity and symbiotic functioning in mungbean (Vigna radiata L. Wilczek) bradyrhizobia from contrast agro-ecological regions of Nepal.

Syst Appl Microbiol 2012 Feb 15;35(1):45-53. Epub 2011 Dec 15.

United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, 183-8509, Japan.

Nepal consists wide range of climatic and topographical variations. Here, we explored the phylogeny of native mungbean bradyrhizobia isolated from different agro-ecological regions of Nepal and accessed their nodulation and nitrogen fixation characteristics. Soil samples were collected from three agro-ecological regions with contrasting climate and topography. A local mungbean cultivar, Kalyan, was used as a trap plant. We characterized isolates based on the full nucleotide sequence of the 16S rRNA, ITS region, and nodA genes; and partial sequences of nodD1 and nifD genes. We found 50% of isolates phylogenetically related to B. yuanmingense, 13% to B. japonicum, 8% to B. elkanii, and 29% to novel phylogenetic origin. Results of the inoculation test suggested that expression of different symbiotic genes in isolates resulted in different degrees of symbiotic functioning. Our results indicate B. yuanmingense and novel strains are more efficient symbiotic partners than B. elkanii for the local mungbean cv. Kalyan. We also found most mungbean rhizobial genotypes were conserved across agro-ecological regions. All the strains from tropical Terai region belonged to B. yuanmingense or a novel lineage of B. yuanmingense, and dominance of B. japonicum related strains was observed in the Hill region. Higher genetic diversity of Bradyrhizobium strains was observed in temperate and sub-tropical region than in the tropical region.
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http://dx.doi.org/10.1016/j.syapm.2011.06.004DOI Listing
February 2012

Phenotypic and genetic characterization of rhizobia associated with alfalfa in the Hokkaido and Ishigaki regions of Japan.

Syst Appl Microbiol 2011 Sep;34(6):453-61

United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.

Twenty five rhizobial isolates were obtained from root nodules of Medicago sativa inoculated with soil samples collected from the Sapporo region and Ishigaki Island in Japan. To study their diversity and characterize them in relation to the climatic conditions of their soils of origin, a polyphasic approach analyzing stress tolerance, symbiotic and genetic properties was used. Stress tolerance assays revealed marked variations in salinity, pH and temperature tolerance. Isolates originating from a sub-tropical climate in alkaline soil (Ishigaki Island) tolerated high temperature, salinity and pH levels. Moreover, isolates recovered from a temperate climate in acidic soil (Sapporo) were sensitive to high temperature and salinity, and tolerated acidic pH. Phylogenetic analysis of conserved 16S rRNA and recA genes, and symbiotic nodA and nifDK revealed 25 isolates to be closely related to Ensifer meliloti. Furthermore, the branch patterns of phylogenetic trees constructed from different genes revealed the existence of at least two E. meliloti types in the soils studied. These results may be relevant to programs directed towards improving crop productivity through biofertilization with locally adapted and genetically defined strains.
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http://dx.doi.org/10.1016/j.syapm.2011.04.006DOI Listing
September 2011

Stress tolerance and symbiotic and phylogenic features of root nodule bacteria associated with Medicago species in different bioclimatic regions of Tunisia.

Microbes Environ 2011 ;26(1):36-45

United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, 3–5–8 Saiwai-cho, Fuchu, Tokyo 183–8509, Japan.

Thirty two rhizobial isolates were obtained from different bioclimatic regions of Tunisia using as trap plants, Medicago sativa, Medicago ciliaris, Medicago polymorpha and Medicago minima. To study their diversity and characterize them in relation to Mediterranean conditions, abiotic stress resistance, symbiotic properties and genetic diversity in terms of 16S rRNA and nodA sequences were assessed. Five isolates from M. sativa, three from M. ciliaris and three from M. minima could grow at 45°C. Only two isolates from M. sativa grew at 4% NaCl. The most stress tolerant isolates were obtained from arid soils. A phylogenetic analysis of 16S rRNA genes revealed 29 isolates to be closely related to Ensifer including one (Pl.3-9) that showed a 16S rRNA sequence similar to that of Ensifer meliloti and nodA sequence similar to that of Ensifer medicae. However, three isolates were categorized into Agrobacterium containing the nodA of Ensifer. Furthermore, these isolates developed nodules on original hosts. The results for the four isolates suggest horizontal gene transfer between the species.
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http://dx.doi.org/10.1264/jsme2.me10138DOI Listing
July 2011

Genetic diversity of native soybean bradyrhizobia from different topographical regions along the southern slopes of the Himalayan Mountains in Nepal.

Syst Appl Microbiol 2010 Nov 18;33(7):416-25. Epub 2010 Sep 18.

United Graduate School of Agri. Science, Tokyo Univ. of Agri. and Tech., Tokyo 183-8509, Japan.

Soybean-nodulating bradyrhizobia are genetically diverse and are classified into different species. In this study, the genetic diversity of native soybean bradyrhizobia isolated from different topographical regions along the southern slopes of the Himalayan Mountains in Nepal was explored. Soil samples were collected from three different topographical regions with contrasting climates. A local soybean cultivar, Cobb, was used as a trap plant to isolate bradyrhizobia. A total of 24 isolates selected on the basis of their colony morphology were genetically characterized. For each isolate, the full nucleotide sequence of the 16S rRNA gene and ITS region, and partial sequences of the nifD and nodD1 genes were determined. Two lineages were evident in the conserved gene phylogeny; one representing Bradyrhizobium elkanii (71% of isolates), and the other representing Bradyrhizobium japonicum (21%) and Bradyrhizobium yuanmingense (8%). Phylogenetic analyses revealed three novel lineages in the Bradyrhizobium elkanii clade, indicating high levels of genetic diversity among Bradyrhizobium isolates in Nepal. B. japonicum and B. yuanmingense strains were distributed in areas from 2420 to 2660 m above sea level (asl), which were mountain regions with a temperate climate. The B. elkanii clade was distributed in two regions; hill regions ranging from 1512 to 1935 m asl, and mountain regions ranging from 2420 to 2660 m asl. Ten multi-locus genotypes were detected; seven among B. elkanii, two among B. japonicum, and one among B. yuanmingense-related isolates. The results indicated that there was higher species-level diversity of Bradyrhizobium in the temperate region than in the sub-tropical region along the southern slopes of the Himalayan Mountains in Nepal.
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http://dx.doi.org/10.1016/j.syapm.2010.06.008DOI Listing
November 2010
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