Rhizobium panacihumi sp. nov., an isolate from ginseng-cultivated soil, as a potential plant growth promoting bacterium.

A novel bacterial strain designated DCY116T was isolated from ginseng-cultivated soil in Gochang-gun, Republic of Korea. Strain DCY116T, belongs to the genus Rhizobium, and is closely related to Rhizobium yantingense H66T (98.3%), Neorhizobium huautlense S02T (98.2%), Rhizobium soli DS-42T (98.1%), Rhizobium smilacinae PTYR-5T (97.9%), and Neorhizobium alkalisoli CCBAU 01393T (97.9%) based on 16S rRNA gene sequence analysis. Analysis of the housekeeping genes atpD, recA, and glnII showed low levels of sequence similarity (96.8%) between strain DCY116T and other closely related species. Strain DCY116T was Gram-stain negative, motile by peritrichous flagella, rod-shaped, strictly aerobic, catalase- and oxidase-positive. Q-10 was the predominant ubiquinone. The major cellular fatty acids were identified as C16:0 and summed feature 8 (C18:1 ω7c and/or C18:1 ω6c). The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, and an unknown lipid (L1-3). Genomic DNA G + C content of strain DCY116T was determined to be 57.2 mol%. DNA-DNA homology values between strain DCY116T and closely related species of the genus Rhizobium were lower than 40%. Strain DCY116T produced indole-3-acetic acid, siderophores, and was able to solubilize phosphate as a potential plant growth promoting bacterium. In conclusion, the results of this study support strain DCY116T as a novel species of the genus Rhizobium, for which the name Rhizobium panacihumi is proposed. The type strain is DCY116T (= KCTC 62017T = JCM 32251T).

Nitrogen-fixing rhizobial strains isolated from Desmodium incanum DC in Argentina: Phylogeny, biodiversity and symbiotic ability.

Desmodium spp. are leguminous plants belonging to the tribe Desmodieae of the subfamily Papilionoideae. They are widely distributed in temperated and subtropical regions and are used as forage plants, for biological control, and in traditional folk medicine. The genus includes pioneer species that resist the xerothermic environment and grow in arid, barren sites. Desmodium species that form nitrogen-fixing symbiosis with rhizobia play an important role in sustainable agriculture. In Argentina, 23 native species of this genus have been found, including Desmodium incanum. In this study, a total of 64 D. incanum-nodulating rhizobia were obtained from root nodules of four Argentinean plant populations. Rhizobia showed different abiotic-stress tolerances and a remarkable genetic diversity using PCR fingerprinting, with more than 30 different amplification profiles. None of the isolates were found at more than one site, thus indicating a high level of rhizobial diversity associated with D. incanum in Argentinean soils. In selected isolates, 16S rDNA sequencing and whole-cell extract MALDI TOF analysis revealed the presence of isolates related to Bradyrhizobium elkanii, Bradyrhizobium japonicum, Bradyrhizobium yuanmingense, Bradyrhizobium liaoningense, Bradyrhizobium denitrificans and Rhizobium tropici species. In addition, the nodC gene studied in the selected isolates showed different allelic variants. Isolates were phenotypically characterized by assaying their growth under different abiotic stresses. Some of the local isolates were remarkably tolerant to high temperatures, extreme pH and salinity, which are all stressors commonly found in Argentinean soils. One of the isolates showed high tolerance to temperature and extreme pH, and produced higher aerial plant dry weights compared to other inoculated treatments. These results indicated that local isolates could be efficiently used for D. incanum inoculation.

Rhizobium smilacinae sp. nov., an endophytic bacterium isolated from the leaf of Smilacina japonica.

During a study of endophytic bacteria from traditional Chinese medicinal plants, a bacterial strain, designated PTYR-5(T), was isolated from the leaf of Smilacina japonica A. Gray collected from Taibai Mountain in Shaanxi Province, north-west China. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PTYR-5(T) is a member of the genus Rhizobium, exhibiting the highest sequence similarities to R. cellulosilyticum LMG 23642(T) (97.2%), R. huautlense LMG 18254(T) (97.2%) and R. alkalisoli CCBAU 01393(T) (97.1%). The levels of 16S rRNA gene sequence similarity with respect to other Rhizobium species with validly published names were less than 97.0%. Phylogenies of the housekeeping genes atpD, recA and glnII confirmed its distinct position, showing low similarity with respect to those of recognized Rhizobium species (no more than 94.1, 90.0 and 88.0% similarity, respectively). The DNA-DNA relatedness values of strain PTYR-5(T) with R. cellulosilyticum LMG 23642(T), R. huautlense LMG 18254(T) and R. alkalisoli CCBAU 01393(T) were 33.6, 21.4 and 29.5 %, respectively. Based on phenotypic, phylogenetic and genotypic data, strain PTYR-5(T) is considered to represent a novel species of the genus Rhizobium, for which the name Rhizobium smilacinae sp. nov. is proposed. The type strain is PTYR-5(T) (=CCTCC AB 2013016(T)=KCTC 32300(T)=LMG 27604(T)).

Microbial abundance and community composition influence production performance in a low-temperature petroleum reservoir.

Enhanced oil recovery using indigenous microorganisms has been successfully applied in the petroleum industry, but the role of microorganisms remains poorly understood. Here, we investigated the relationship between microbial population dynamics and oil production performance during a water flooding process coupled with nutrient injection in a low-temperature petroleum reservoir. Samples were collected monthly over a two-year period. The microbial composition of samples was determined using 16S rRNA gene pyrosequencing and real-time quantitative polymerase chain reaction analyses. Our results indicated that the microbial community structure in each production well microhabitat was dramatically altered during flooding with eutrophic water. As well as an increase in the density of microorganisms, biosurfactant producers, such as Pseudomonas, Alcaligenes, Rhodococcus, and Rhizobium, were detected in abundance. Furthermore, the density of these microorganisms was closely related to the incremental oil production. Oil emulsification and changes in the fluid-production profile were also observed. In addition, we found that microbial community structure was strongly correlated with environmental factors, such as water content and total nitrogen. These results suggest that injected nutrients increase the abundance of microorganisms, particularly biosurfactant producers. These bacteria and their metabolic products subsequently emulsify oil and alter fluid-production profiles to enhance oil recovery.

Rhizobium calliandrae sp. nov., Rhizobium mayense sp. nov. and Rhizobium jaguaris sp. nov., rhizobial species nodulating the medicinal legume Calliandra grandiflora.

Calliandra grandiflora has been used as a medicinal plant for thousands of years in Mexico. Rhizobial strains were obtained from root nodules of C. grandiflora collected from different geographical regions in Chiapas and characterized by BOX-PCR, amplified rDNA restriction analysis (ARDRA) and 16S rRNA gene sequence analysis. Most isolates corresponded to members of the genus Rhizobium and those not related to species with validly published names were further characterized by recA, atpD, rpoB and nifH gene phylogenies, phenotypic and DNA-DNA hybridization analyses. Three novel related species of the genus Rhizobium within the 'Rhizobium tropici group' share the same symbiovar that may be named sv. calliandrae. The names proposed for the three novel species are Rhizobium calliandrae sp. nov. (type strain, CCGE524(T) =ATCC BAA-2435(T) =CIP 110456(T) =LBP2-1(T)), Rhizobium mayense sp. nov. (type strain, CCGE526(T) =ATCC BAA-2446(T) = CIP 110454(T) =NSJP1-1(T)) and Rhizobium jaguaris sp. nov. (type strain, CCGE525(T) =ATCC BAA-2445(T) =CIP 110453(T) =SJP1-2(T)).

Diversity of rhizobia associated with leguminous trees growing in South Korea.

This study was carried out to examine the diversity of 34 isolates collected from 11 species of leguminous trees growing in South Korea. Phylogenetic relationships between these 34 isolates and reference strains of the Azorhizobium, Bradyrhizobium, Mesorhizobium, Rhizobium and Ensifer/Sinorhizobium were analysed by using 16S rRNA gene sequences. Twenty-one isolates were related to Mesorhizobium, four isolates to Rhizobium, and nine isolates to Bradyrhizobium. But none of isolates were related to Sinorhizobium/Ensifer and Azorhizobium. Robinia pseudoacacia and Amorpha fruticosa were nodulated by various genotypes of rhizobia out of them, most of the isolates belonged to the genus Mesorhizobium. The isolates from Lespedeza bicolar belonged to diverse genera of Mesorhizobium, Rhizobium, and Bradyrhizobium. The isolates from Maackia amurensis and Lespedeza maximowiezii var. tomentella were phylogenetically related to the genera of Bradyrhizobium. PCR-based RAPD method and phylogenetic analysis of the 16S rRNA results revealed a high phylogenetic diversity of rhizobial strains nodulating leguminous trees in South Korea. Also, the relationships between host and bacterial phylogenies showed that only Robinia pseudoacacia, and Wisteria floribunda have significantly unique branch length than expected by chance based on phylogenetic tree.

Biogeography of symbiotic and other endophytic bacteria isolated from medicinal Glycyrrhiza species in China.

A total of 159 endophytic bacteria were isolated from surface-sterilized root nodules of wild perennial Glycyrrhiza legumes growing on 40 sites in central and northwestern China. Amplified fragment length polymorphism (AFLP) genomic fingerprinting and sequencing of partial 16S rRNA genes revealed that the collection mainly consisted of Mesorhizobium, Rhizobium, Sinorhizobium, Agrobacterium and Paenibacillus species. Based on symbiotic properties with the legume hosts Glycyrrhiza uralensis and Glycyrrhiza glabra, we divided the nodulating species into true and sporadic symbionts. Five distinct Mesorhizobium groups represented true symbionts of the host plants, the majority of strains inducing N2-fixing nodules. Sporadic symbionts consisted of either species with infrequent occurrence (Rhizobium galegae, Rhizobium leguminosarum) or species with weak (Sinorhizobium meliloti, Rhizobium gallicum) or no N2 fixation ability (Rhizobium giardinii, Rhizobium cellulosilyticum, Phyllobacterium sp.). Multivariate analyses revealed that the host plant species and geographic location explained only a small part (14.4%) of the total variation in bacterial AFLP patterns, with the host plant explaining slightly more (9.9%) than geography (6.9%). However, strains isolated from G. glabra were clearly separated from those from G. uralensis, and strains obtained from central China were well separated from those originating from Xinjiang in the northwest, indicating both host preference and regional endemism.

Gene transfer into Solanum tuberosum via Rhizobium spp.

Agrobacterium tumefaciens-mediated transformation (ATMT) is the preferred technique for gene transfer into crops. A major disadvantage of the technology remains the complexity of the patent landscape that surrounds ATMT which restricts its use for commercial applications. An alternative system has been described (Broothaerts et al. in Nature 433:629-633, 2005) detailing the propensity of three rhizobia to transform the model crop Arabidopsis thaliana, the non-food crop Nicotiana tabacum and, at a very low frequency, the monocotyledonous crop Oryza sativa. In this report we describe for the first time the genetic transformation of Solanum tuberosum using the non-Agrobacterium species Sinorhizobium meliloti, Rhizobium sp. NGR234 and Mesorhizobium loti. This was achieved by combining an optimal bacterium and host co-cultivation period with a low antibiotic regime during the callus and shoot induction stages. Using this optimized protocol the transformation frequency (calculated as % of shoots equipped with root systems with the ability to grow in rooting media supplemented with 25 µg/ml hygromycin) of the rhizobia strains was calculated at 4.72, 5.85 and 1.86% for S. meliloti, R. sp. NGR234 and M. loti respectively, compared to 47.6% for the A. tumefaciens control. Stable transgene integration and expression was confirmed via southern hybridisation, quantitative PCR analysis and histochemical screening of both leaf and/or tuber tissue. In light of the rapid advances in potato genomics, combined with the sequencing of the potato genome, the ability of alternative bacteria species to genetically transform this major food crop will provide a novel resource to the Solanaceae community as it continues to develop potato as both a food and non-food crop.

Rhizobium phenanthrenilyticum sp. nov., a novel phenanthrene-degrading bacterium isolated from a petroleum residue treatment system.

Strain F11(T), a phenanthrene-degrading bacterium, was isolated from a petroleum residue treatment system, and classified under the genus Rhizobium based on the similarity analysis of its 16S rRNA and recA gene sequences. Strain F11(T) falls into the same phylogenetic clade with Rhizobium oryzae Alt 505(T) (96.8% 16S rRNA gene sequence similarity) and Rhizobium pseudoryzae J34A-127(T) (96.2%). Major cellular fatty acids of strain F11(T) are C(16:0) (6.24%) and summed feature 8 (C(18:1ω7c) and/or C(18:1ω6c), 76.59%), which are also the major fatty acids of R. oryzae Alt 505(T) and R. pseudoryzae J34A-127(T). The DNA G+C content of strain F11(T) was 59.3±0.4 mol%. Based on the phylogenetic analysis as well as biochemical and physiological characteristics, strain F11(T) could be separated from all recognized Rhizobium species. Strain F11(T) (=DSM 21882(T) =CCTCC AB 209029(T)) was considered to be representative of a novel species of Rhizobium, for which the name Rhizobium phenanthrenilyticum sp. nov. is proposed.

Reduction of selenite to elemental red selenium by Rhizobium sp. strain B1.

A bacterium that reduces the soluble and toxic selenite anion to insoluble elemental red selenium (Se(0)) was isolated from a laboratory bioreactor. Biochemical, morphological, and 16S rRNA gene sequence alignment identified the isolate as a Rhizobium sp. that is related to but is genetically divergent from R. radiobacter (syn. Agrobacterium tumefaciens) or R. rubi (syn. A. rubi). The isolate was capable of denitrification and reduced selenite to Se(0) under aerobic and denitrifying conditions. It did not reduce selenate and did not use selenite or selenate as terminal e(-) donors. Native gel electrophoresis revealed two bands, corresponding to molecular weights of approximately 100 and approximately 45 kDa, that reduced selenite. Tungsten inhibited in vivo selenite reduction, suggesting that a molybdenum-containing protein is involved in selenite reduction. This organism, or its enzymes or DNA, might be useful in bioreactors designed to remove selenite from water.

Rhizobium selenireducens sp. nov.: a selenite-reducing alpha-Proteobacteria isolated from a bioreactor.

A Gram-negative, nonpigmented bacterium designated strain B1 was isolated from a laboratory bioreactor that reduced selenate to elemental red selenium (Se(0)). 16S rRNA gene-sequence alignment identified the isolate as a Rhizobium sp. belonging to the Rhizobium clade, which includes R. daejeonense, R. giardinii, R. undicola, R. larrymoorei, R. radiobacter, R. rubi, and R. vitis. R. radiobacter and R. rubi are its closest relatives as indicated by 16S rRNA gene-sequence alignments, which differ from strain B1 by 2.6% and 2.8%, respectively. Within this group, strains that show variances > 0.8% to 2.2% have been classified as different species. The major cellular fatty acids present in the B1 strain were C16:0 (1.8%), C18:0 (3.38%), 18:0 3-OH (1.6%), 18:1 omega7c (86.8%), 19:0 cycloomega8c (1.5%), and summed features 2 (3.8%) and 3 (1.2%). The large amount of 18:1 omega7c present is constant with members of this group of bacteria, but the small amounts of 16:0, 19:0 cycloomega8c, and summed feature 3 shows variance from R. radiobacter and R. rubi. The strain's phenotypic and biochemical characteristics are consistent with its placement in this genus.

Genetic diversity of rhizobia associated with Desmodium species grown in China.

AIMS: Desmodia are leguminous plants used as important forage and herbal medicine in China. Little information is available about the nodule bacteria of Desmodium species. To understand the genetic diversity of rhizobia associated with Desmodium species grown in China, isolates from temperate and subtropical regions were obtained and analysed. METHODS AND RESULTS: A total of 39 rhizobial strains isolated from 9 Desmodium species grown in China were characterized by PCR-based 16S rDNA gene and 16S-23S rDNA intergenic spacer gene restriction fragment length polymorphism (RFLP) and 16S rRNA gene sequencing. The results showed high diversity among rhizobia symbiotic with Desmodium species. Most microsymbionts of Desmodium species belonged to Bradyrhizobium closely related to Bradyrhizobium elkanii, Bradyrhizobium japonicum and Bradyrhizobium yuanmingense. Several small groups or single strain were related to Rhizobium, Sinorhizobium or Mesorhizobium. CONCLUSIONS: Desmodium species formed nodules with diverse rhizobia in Chinese soils. SIGNIFICANCE AND IMPACT OF THE STUDY: These results offered the first systematic information about the microsymbionts of desmodia grown in the temperate and subtropical regions of China.

Rhizobium yanglingense sp. nov., isolated from arid and semi-arid regions in China.

A novel rhizobial group, cluster 9, defined in previous research [Tan, Z. Y., Wang, E. T., Peng, G. X., Zhu, M. E., Martinez-Romero, E. & Chen, W. X. (1999). Int J Syst Bacteriol 49, 1457-1469], was further characterized by determination of DNA base composition, whole-cell protein SDS-PAGE analysis, DNA-DNA hybridization, 16S rRNA gene sequencing and host specificity. These isolates were collected from the wild legumes Amphicarpaea trisperma, Coronilla varia and Gueldenstaedtia multiflora growing in arid and semi-arid regions in northwestern China. Isolates within cluster 9 grouped into a single cluster above a similarity level of 90.6% in a cluster analysis based on protein SDS-PAGE, and they were differentiated from defined rhizobial species. Comparative analysis of 16S rRNA gene sequences showed that isolate CCBAU 71623T, representing cluster 9, was most related to Rhizobium gallicum and Rhizobium mongolense. The DNA-DNA homologies were lower than 42.4% among cluster 9 and defined species, including R. gallicum and R. mongolense. These data indicated that cluster 9 was a unique genomic species. Isolates within this cluster could share their host plants. They could not nodulate Galega orientalis and Leucaena leucocephala and formed ineffective nodules on Phaseolus vulgaris. This group could also be differentiated from defined species by phenotypic characteristics. It is therefore proposed as a new species, Rhizobium yanglingense, with isolate CCBAU 71623 as the type strain.

Decreased scopolamine yield in field-grown Duboisia plants regenerated from hairy roots.

Hairy root cultures were obtained from hybrid clones of Duboisia myoporoides x D. leichhardtii following transformation by Agrobacterium rhizogenes strain A4. Shoots spontaneously regenerating from the hairy root cultures were rooted and transferred to soil. The plants displayed typical morphological alterations known as hairy root syndrome to varying degrees. PCR analysis confirmed that all transformed plants contained the rolA, rolB and rolC genes, irrespective of the degree of morphological alterations. A field test of the transformed regenerated plants revealed that those plants displaying the strongest hairy root syndrome symptoms had the highest content of the tropane alkaloid scopolamine. However, the overall scopolamine and hyoscyamine yield of all transformed plants was clearly reduced compared to untransformed control plants. These results demonstrate that the A. rhizogenes-transformed plants tested in this study do not provide a viable alternative to agricultural farming of hybrid clones of D. myoporoides x D. leichhardtii obtained by conventional breeding.

Characterization of rhizobial isolates of Phaseolus vulgaris by staircase electrophoresis of low-molecular-weight RNA.

Low-molecular-weight (LMW) RNA molecules were analyzed to characterize rhizobial isolates that nodulate the common bean growing in Spain. Since LMW RNA profiles, determined by staircase electrophoresis, varied across the rhizobial species nodulating beans, we demonstrated that bean isolates recovered from Spanish soils presumptively could be characterized as Rhizobium etli, Rhizobium gallicum, Rhizobium giardinii, Rhizobium leguminosarum bv. viciae and bv. trifolii, and Sinorhizobium fredii.

Novel tellurite-amended media and specific chromosomal and Ti plasmid probes for direct analysis of soil populations of Agrobacterium biovars 1 and 2.

Ecology and biodiversity studies of Agrobacterium spp. require tools such as selective media and DNA probes. Tellurite was tested as a selective agent and a supplement of previously described media for agrobacteria. The known biodiversity within the genus was taken into account when the selectivity of K(2)TeO(3) was analyzed and its potential for isolating Agrobacterium spp. directly from soil was evaluated. A K(2)TeO(3) concentration of 60 ppm was found to favor the growth of agrobacteria and restrict the development of other bacteria. Morphotypic analyses were used to define agrobacterial colony types, which were readily distinguished from other colonies. The typical agrobacterial morphotype allowed direct determination of the densities of agrobacterial populations from various environments on K(2)TeO(3)-amended medium. The bona fide agrobacterium colonies growing on media amended with K(2)TeO(3) were confirmed to be Agrobacterium colonies by using 16S ribosomal DNA (rDNA) probes. Specific 16S rDNA probes were designed for Agrobacterium biovar 1 and related species (Agrobacterium rubi and Agrobacterium fici) and for Agrobacterium biovar 2. Specific pathogenic probes from different Ti plasmid regions were used to determine the pathogenic status of agrobacterial colonies. Various morphotype colonies from bulk soil suspensions were characterized by colony blot hybridization with 16S rDNA and pathogenic probes. All the Agrobacterium-like colonies obtained from soil suspensions on amended media were found to be bona fide agrobacteria. Direct colony counting of agrobacterial populations could be done. We found 10(3) to 10(4) agrobacteria. g of dry soil(-1) in a silt loam bulk soil cultivated with maize. All of the strains isolated were nonpathogenic bona fide Agrobacterium biovar 1 strains.

Small-subunit rRNA genotyping of rhizobia nodulating Australian Acacia spp.

The structure of rhizobial communities nodulating Acacia in southeastern Australia from south Queensland to Tasmania was investigated by a molecular approach. A total of 118 isolates from nodule samples from 13 different Acacia species collected at 44 sites were characterized by small-subunit (SSU) ribosomal DNA (rDNA) PCR-restriction fragment length polymorphism analysis. Nine rhizobial genomospecies were identified, and these taxa corresponded to previously described genomospecies (B. Lafay and J. J. Burdon, Appl. Environ. Microbiol. 64:3989-3997, 1998). Eight of these genomospecies belonged to the Bradyrhizobium lineage and accounted for 96.6% of the isolates. The remaining genomospecies corresponded to Rhizobium tropici. For analysis of geographic patterns, results were grouped into five latitudinal regions regardless of host origin. In each region, as observed previously for rhizobial isolates taken from non-Acacia legumes (Lafay and Burdon, Appl. Environ. Microbiol. 64:3989-3997, 1998), rhizobial communities were dominated by one or two genomospecies, the identities of which varied from place to place. Despite this similarity in patterns, the most abundant genomospecies for Acacia isolates differed from the genomospecies found in the non-Acacia-derived rhizobial collection, suggesting that there is a difference in nodulation patterns of the Mimosoideae and the Papilionoideae. Only two genomospecies were both widespread and relatively abundant across the range of sites sampled. Genomospecies A was found in all regions except the most northern sites located in Queensland, whereas genomospecies B was not detected in Tasmania. This suggests that genomospecies A might be restricted to the more temperate regions of Australia, whereas in contrast, genomospecies B occurs in different climatic and edaphic conditions across the whole continent. The latter hypothesis is supported by the presence of genomospecies B in southwestern Australia, based on partial SSU rDNA sequence data (N. D. S. Marsudi, A. R. Glenn, and M. J. Dilworth, Soil Biol. Biochem. 31:1229-1238, 1998).

[Genetic transformation of hairy roots in Trichosanthes kirilowii Maxim. by Ti and Ri plasmids].

OBJECTIVE: To establish a hairy root culture system by double transformation for Trichosanthes kirilowii. METHOD: 1. Crown galls were induced by direct infection of sterile seedlings of T. kirilonii with Agrobacterium tumefaciens C58, and then the hairy roots were obtained from the regenerated plants by infection with A. rhzogenes 15834; 2. Transformation of Ti and Ri plasmids was inspected by high-pressure-paper electrophoresis; 3. The protein contents in the tissues of T. kirilowii were inspected by spectrophotometer and SDS-PAGE. RESULT: A hairy root culture system has been established successfully by double transformation with Ti and Ri plasmids in T. kirilowii. CONCLUSION: Compared with the ordinary hairy roots, the double transformed hairy roots grow faster but retain similar protein contents.

Numerical taxonomy of Sarothamnus scoparius rhizobia.

Twenty nodule isolates from Sarothamnus scoparius (broom) growing in Poland and nine strains from plants growing in Japan were studied for phenotypic properties, plasmid presence, phage sensitivity, and host plant specificity. By numerical analysis of phenotypic properties, it was found that the studied nodule bacteria, originating from geographically different countries, constitute two separate groups affiliated to the bradyrhizobium cluster. The membership of S. scoparius rhizobia in the Bradyrhizobium genus was also supported by their long generation time, alkaline reaction in YEM medium with mannitol, lack of plasmids, and wide host plant range.

Symbiosis of Astragalus cicer with its microsymbionts: partial nodC gene sequence, host plant specificity, and root nodule structure.

Astragalus cicer (cicer milkvetch) nodule bacteria were investigated for host plant specificity and partial nodC gene sequences, whilst their native host was studied for the microscopic structure of root nodules. The strains under investigation formed nodules not only on the original host but also on Astragalus glycyphyllos, Astragalus sinicus, Lotus corniculatus, and Phaseolus vulgaris. The nodules induced on the cicer milkvetch were classified as indeterminate and characterized by apical, persistent meristem, a large bacteroid region with infected and uninfected cells, and elongated bacteroids singly located inside peribacteroid membranes. By comparison of the partial nodC gene sequences of a representative strain of astragali rhizobia to those contained in the GenBank database, a close symbiotic relationship of A. cicer microsymbionts to Rhizobium sp. (Oxytropis) was found.