Dynamic bacterial community response to Akashiwo sanguinea (Dinophyceae) bloom in indoor marine microcosms.

We investigated the dynamics of the bacterial composition and metabolic function within Akashiwo sanguinea bloom using a 100-L indoor microcosm and metagenomic next-generation sequencing. We found that the bacterial community was classified into three groups at 54% similarity. Group I was associated with "during the A. sanguinea bloom stage" and mainly consisted of Alphaproteobacteria, Flavobacteriia and Gammaproteobacteria. Meanwhile, groups II and III were associated with the "late bloom/decline stage to post-bloom stage" with decreased Flavobacteriia and Gammaproteobacteria in these stages. Upon the termination of the A. sanguinea bloom, the concentrations of inorganic nutrients (particularly PO43-, NH4+ and dissolved organic carbon) increased rapidly and then decreased. From the network analysis, we found that the A. sanguinea node is associated with certain bacteria. After the bloom, the specific increases in NH4+ and PO43- nodes are associated with other bacterial taxa. The changes in the functional groups of the bacterial community from chemoheterotrophy to nitrogen association metabolisms were consistent with the environmental impacts during and after A. sanguinea bloom. Consequently, certain bacterial communities and the environments dynamically changed during and after harmful algal blooms and a rapid turnover within the bacterial community and their function can respond to ecological interactions.

Steel slag amendment impacts on soil microbial communities and activities of rice (Oryza sativa L.).

With the increase in iron/steel production, the higher volume of by-products (slag) generated necessitates its efficient recycling. Because the Linz-Donawitz (LD) slag is rich in silicon (Si) and other fertilizer components, we aim to evaluate the impact of the LD slag amendment on soil quality (by measuring soil physicochemical and biological properties), plant nutrient uptake, and strengthens correlations between nutrient uptake and soil bacterial communities. We used 16 S rRNA illumine sequencing to study soil bacterial community and APIZYM assay to study soil enzymes involved in C, N, and P cycling. The LD slag was applied at 2 Mg ha-1 to Japonica and Indica rice cultivated under flooded conditions. The LD slag amendment significantly improved soil pH, plant photosynthesis, soil nutrient availability, and the crop yield, irrespective of cultivars. It significantly increased N, P, and Si uptake of rice straw. The slag amendment enhanced soil microbial biomass, soil enzyme activities and enriched certain bacterial taxa featuring copiotrophic lifestyles and having the potential role for ecosystem services provided to the benefit of the plant. The study evidenced that the short-term LD slag amendment in rice cropping systems is useful to improve soil physicochemical and biological status, and the crop yield.

Croceibacterium gen. nov., with description of Croceibacterium ferulae sp. nov., an endophytic bacterium isolated from Ferula sinkiangensis K. M. Shen and reclassification of Porphyrobacter mercurialis as Croceibacterium mercuriale comb. nov.

A novel endophytic bacterium, designated strain SX2RGS8T, was isolated from the surface-sterilized roots of an endangered medicinal plant (Ferula sinkiangensis K. M. Shen) collected from Xinjiang, north-western PR China. The taxonomic position of the candidate was investigated using a polyphasic approach. Strain SX2RGS8T was found to be aerobic, Gram-stain-negative, oxidase-negative, catalase-positive and axiolitic-shaped. Strain SX2RGS8T grew at 4-45 °C (optimum, 28 °C), pH 4.0-10.0 (pH 7.0) and in the presence of 0-5 % (w/v) NaCl. The polar lipids detected for strain SX2RGS8T were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, unidentified phosphoglycolipids, an unidentified phospholipid and unidentified lipids. The major respiratory quinone of strain SX2RGS8T was ubiquinone 10 and the major fatty acid was summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c). The DNA G+C content was determined to be 66.5 mol%. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the isolate belonged to the family Erythrobacteraceae and showed 99.2 % (Porphyrobacter mercurialis), 95.5 % (Porphyrobacter donghaensisi) and 95.4 % (Porphyrobacter colymbi) similarities to its closest relatives. The isolate contained carotenoids, but no bacteriochlorophyll a. On the basis of phenotypic, genotypic and phylogenetic data, strain SX2RGS8T represents a novel species of a novel genus in the family Erythrobacteraceae, for which the name Croceibacterium ferulae gen. nov., sp. nov. is proposed. The type strain is SX2RGS8T (=CGMCC 1.16402T=KCTC 62090T). In addition, Porphyrobacter mercurialis Coil et al. 2016 is proposed to be transferred to this new genus as Croceibacterium mercuriale comb. nov.

Evaluation of multifarious plant growth promoting traits, antagonistic potential and phylogenetic affiliation of rhizobacteria associated with commercial tea plants grown in Darjeeling, India.

Plant growth promoting rhizobacteria (PGPR) are studied in different agricultural crops but the interaction of PGPR of tea crop is not yet studied well. In the present study, the indigenous tea rhizobacteria were isolated from seven tea estates of Darjeeling located in West Bengal, India. A total of 150 rhizobacterial isolates were screened for antagonistic activity against six different fungal pathogens i.e. Nigrospora sphaerica (KJ767520), Pestalotiopsis theae (ITCC 6599), Curvularia eragostidis (ITCC 6429), Glomerella cingulata (MTCC 2033), Rhizoctonia Solani (MTCC 4633) and Fusarium oxysporum (MTCC 284), out of which 48 isolates were antagonist to at least one fungal pathogen used. These 48 isolates exhibited multifarious antifungal properties like the production of siderophore, chitinase, protease and cellulase and also plant growth promoting (PGP) traits like IAA production, phosphate solubilization, ammonia and ACC deaminase production. Amplified ribosomal DNA restriction analysis (ARDRA) and BOX-PCR analysis based genotyping clustered the isolates into different groups. Finally, four isolates were selected for plant growth promotion study in two tea commercial cultivars TV-1 and Teenali-17 in nursery conditions. The plant growth promotion study showed that the inoculation of consortia of these four PGPR isolates significantly increased the growth of tea plant in nursery conditions. Thus this study underlines the commercial potential of these selected PGPR isolates for sustainable tea cultivation.

Effect of halotolerant rhizobacteria isolated from halophytes on the growth of sugar beet (Beta vulgaris L.) under salt stress.

Utilization of rhizobacteria that have associated with plant roots in harsh environments could be a feasible strategy to deal with limits to agricultural production caused by soil salinity. Halophytes occur naturally in high-salt environments, and their roots may be associated with promising microbial candidates for promoting growth and salt tolerance in crops. This study aimed to isolate efficient halotolerant plant-growth-promoting rhizobacterial strains from halophytes and evaluate their activity and effects on sugar beet (Beta vulgaris L.) growth under salinity stress. A total of 23 isolates were initially screened for their ability to secrete 1-aminocyclopropane-1-carboxylate deaminase (ACD) as well as other plant-growth-promoting characteristics and subsequently identified by sequencing the 16S rRNA gene. Three isolates, identified as Micrococcus yunnanensis, Planococcus rifietoensis and Variovorax paradoxus, enhanced salt stress tolerance remarkably in sugar beet, resulting in greater seed germination and plant biomass, higher photosynthetic capacity and lower stress-induced ethylene production at different NaCl concentrations (50-125 mM). These results demonstrate that salinity-adapted, ACD-producing bacteria isolated from halophytes could promote sugar beet growth under saline stress conditions.

Environmental Enrichment Induces Pericyte and IgA-Dependent Wound Repair and Lifespan Extension in a Colon Tumor Model.

Environmental enrichment (EE) replicates mind-body therapy by providing complex housing to laboratory animals to improve their activity levels, behavior, and social interactions. Using a Tcf4Het/+ApcMin/+-mediated model of colon tumorigenesis, we found that EE vastly improved the survival of tumor-bearing animals, with differential effect on tumor load in male compared to female animals. Analysis of Tcf4Het/+ApcMin/+ males showed drastically reduced expression of circulating inflammatory cytokines and induced nuclear hormone receptor (NHR) signaling, both of which are common in the wound repair process. Interestingly, EE provoked tumor wound repair resolution through revascularization, plasma cell recruitment and IgA secretion, replacement of glandular tumor structures with pericytes in a process reminiscent of scarring, and normalization of microbiota. These EE-dependent changes likely underlie the profound improvement in survival of colon-tumor-bearing Tcf4Het/+ApcMin/+ males. Our studies highlight the exciting promise of EE in the design of future therapeutic strategies for colon cancer patients.

Plant powder teabags: a novel and practical approach to resolve culturability and diversity of rhizobacteria.

We have developed teabags packed with dehydrated plant powders, without any supplements, for preparation of plant infusions necessary to develop media for culturing rhizobacteria. These bacteria are efficiently cultivated on such plant teabag culture media, with better progressive in situ recoverability compared to standard chemically synthetic culture media. Combining various plant-based culture media and incubation conditions enabled us to resolve unique denaturing gradient gel electrophoresis (DGGE) bands that were not resolved by tested standard culture media. Based on polymerase chain reaction PCR-DGGE of 16S rDNA fingerprints and sequencing, the plant teabag culture media supported higher diversity and significant increases in the richness of endo-rhizobacteria, namely Gammaproteobacteria (Enterobacteriaceae) and predominantly Alphaproteobacteria (Rhizobiaceae). This culminated in greater retrieval of the rhizobacteria taxa associated with the plant roots. We conclude that the plant teabag culture medium by itself, without any nutritional supplements, is sufficient and efficient for recovering and mirroring the complex and diverse communities of rhizobacteria. Our message to fellow microbial ecologists is: simply dehydrate your plant canopy, teabag it and soak it to prepare your culture media, with no need for any additional supplementary nutrients.

Review - Lichen-Associated Bacteria as a Hot Spot of Chemodiversity: Focus on Uncialamycin, a Promising Compound for Future Medicinal Applications.

This review presents the state of knowledge on the medicinal potential of bacteria associated with lichens. In fact, besides the classical symbiotic partners (photobiont and mycobiont) forming the lichen thallus, associated bacteria have been recently described as a third partner. Various studies demonstrated the diversity of these communities with a predominance of Alphaproteobacteria. Bacterial groups more relevant for secondary metabolite synthesis have also been revealed. This article summarizes studies reporting the abilities of these communities to produce metabolites with relevant bioactivities. The biotechnological interest of these bacteria for drug discovery is highlighted regarding the production of compounds with therapeutic potential. Special focus is given to the synthesis of the most promising compound, uncialamycin, a potent enediyne isolated from a Streptomyces sp. associated with Cladonia uncialis.

Glycocaulis alkaliphilus sp. nov., a dimorphic prosthecate bacterium isolated from crude oil.

A bacterial strain designated 6B-8(T) was isolated from crude oil from Daqing oilfield, China. Cells of strain 6B-8(T) were Gram-negative, aerobic, dimorphic and reproduced by means of binary fission. Strain 6B-8(T) could grow at 20-37 °C, pH 8-10 and 1-5 % (w/v) NaCl. Its genomic DNA G+C content was 62.0 mol%. The predominant cellular fatty acids were C18 : 1ω7c, C17 : 0, C18 : 0 and 11-methyl C18 : 1ω7c and the main hydroxy fatty acids were C12 : 0 3-OH and C12 : 1 3-OH when grown on marine agar 2216. The major quinone was Q-10 and the major polar lipids were three unidentified glycolipids. Phylogenetic analysis revealed that strain 6B-8(T) was a member of the family Hyphomonadaceae, sharing 99.6 and 99.4 % 16S rRNA gene sequence similarity with Glycocaulis abyssi LMG 27140(T) and Glycocaulis albus SLG210-30A1(T), respectively, and less than 94.4 % similarity with the type strains of other members of the family Hyphomonadaceae. However, the DNA-DNA relatedness between strain 6B-8(T) and related strains G. abyssi LMG 27140(T) and G. albus SLG210-30A1(T) was 36±5 and 42±5 %, respectively. In addition, several phenotypic and genotypic features allowed differentiation of strain 6B-8(T) from G. abyssi LMG 27140(T) and G. albus SLG210-30A1(T). Therefore, strain 6B-8(T) represents a novel species of genus Glycocaulis, for which the name Glycocaulis alkaliphilus sp. nov. is proposed. The type strain is 6B-8(T) ( = CGMCC 1.12428(T) = LMG 27410(T)).

Glycocaulis albus sp. nov., a moderately halophilic dimorphic prosthecate bacterium isolated from petroleum-contaminated saline soil.

Two novel bacterial strains, SLG210-30A1(T) and SLG210-19A2, which shared 99.9 % 16S rRNA gene sequence similarity with each other, were isolated from petroleum-contaminated saline soil in Shengli Oilfield, eastern China. Cells were Gram-stain-negative, motile, aerobic, mesophilic and moderately halophilic. They could grow chemoheterotrophically with oxygen as an electron acceptor. Morphologically, cells were typical Caulobacteria-type dimorphic prosthecate bacteria. The genomic DNA G+C contents of strains SLG210-30A1(T) and SLG210-19A2 were 61.8 mol% and 61.6 mol% respectively. Strain SLG210-30A1(T) had Q10 as the predominant respiratory ubiquinone, and C16 : 0 (28.4 %), C17 : 0 (11.6 %), C18 : 0 (22.1 %) and C18 : 1ω7c (14.0 %) as the major cellular fatty acids. The polar lipids of the two isolates were some glycolipids, a lipid, a phospholipid, an aminoglycolipid and an aminophospholipid (all unidentified). The 16S rRNA gene sequences of strains SLG210-30A1(T) and SLG210-19A2 showed the highest similarities with Glycocaulis abyssi MCS 33(T) (99.8-99.9 %), but low sequence similarities (<94.7 %) with type strains of other members of the family Hyphomonadaceae. However, the DNA-DNA relatedness of G. abyssi MCS 33(T) to strains SLG210-30A1(T) and SLG210-19A2 was 37.4±4.4 % and 36.1±1.1 %, respectively. Based on different physiological, biochemical, and phylogenetic characteristics, strains SLG210-30A1(T) and SLG210-19A2 represent a novel species of the genus Glycocaulis. The name Glycocaulis albus is therefore proposed with strain SLG210-30A1(T) ( = LMG 27741(T) = CGMCC 1.12766(T)) as the type strain. An emended description of the genus Glycocaulis is also provided.

An assessment of the diversity of culturable bacteria from main root of sugar beet.

The partial sequences of the 16S rRNA genes of 531 bacteria isolated from the main root of the sugar beet (Beta vulgaris L.) were determined and subsequently grouped into 155 operational taxonomic units by clustering analysis (≥99% identity). The most abundant phylum was Proteobacteria (72.5-77.2%), followed by Actinobacteria (9.8-16.6%) and Bacteroidetes (4.3-15.4%). Alphaproteobacteria (46.7-64.8%) was the most dominant class within Proteobacteria. Four strains belonging to Verrucomicrobia were also isolated. Phylogenetic analysis revealed that the Verrucomicrobia bacterial strains were closely related to Haloferula or Verrucomicrobium.

Algimonas ampicilliniresistens sp. nov., isolated from the red alga Porphyra yezoensis, and emended description of the genus Algimonas.

Three strains (14A-2-7(T), 14A-3-1 and 14A-3) of Gram-stain-negative, prosthecate, motile bacteria were isolated from an algal medium supplemented with 10 mg ampicillin l(-1) (w/v), in which the red alga Porphyra yezoensis had been cultured. Based on the 16S rRNA gene sequence analysis, the three isolates formed a cluster with the genus Algimonas of the family Hyphomonadaceae. The sequences of the three isolates had high similarity with those of Algimonas porphyrae 0C-2-2(T) (97.6 % similarity) and Litorimonas taeanensis G5(T) (95.6 % similarity). The DNA G+C contents of the three isolates ranged from 54.3 to 55.0 mol%, which were more similar to that of A. porphyrae 0C-2-2(T) (58.5 mol%) than to that of L. taeanensis G5(T) (47.1 mol%). The DNA-DNA relatedness showed that the three isolates were representatives of the same species (88.1-94.0 % relatedness) and that strain 14A-2-7(T) was a representative of a different species from A. porphyrae 0C-2-2(T) and L. taeanensis G5(T) (1.2-8.6 % relatedness). The phenotypic characteristics of strain 14A-2-7(T) differed by 20 results and 30 results from A. porphyrae 0C-2-2(T) and L. taeanensis G5(T), respectively. The three isolates contained ubiquinone-10 as the predominant quinone and C18 : 1ω7c as the major fatty acid. Based on the polyphasic taxonomic analysis, the three isolates represent a novel species of the genus Algimonas, for which the name Algimonas ampicilliniresistens sp. nov. is proposed. The type strain is 14A-2-7(T) ( = LMG 26421(T) = NBRC 108219(T)). An emended description of the genus Algimonas is also proposed.

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.

Genetic diversity, community structure and distribution of rhizobia in the root nodules of Caragana spp. from arid and semi-arid alkaline deserts, in the north of China.

The genetic diversity of 88 Caragana nodule rhizobial isolates, collected from arid and semi-arid alkaline sandy soils in the north of China, was assessed by PCR-RFLP of the 16S rRNA gene and the 16S-23S IGS, as well as the phylogenies of housekeeping genes (atpD, glnII and recA) and symbiotic genes (nodC and nifH). Of the 88 strains, 69 were placed in the genus Mesorhizobium, 16 in Rhizobium and 3 in Bradyrhizobium. Mesorhizobium amorphae, Mesorhizobium septentrionale, Mesorhizobium temperatum and Rhizobium yanglingense were the four predominant microsymbionts associated with Caragana spp. in the surveyed regions, and M. septentrionale was widely distributed among the sampling sites. Phylogenies of nodC and nifH genes showed that two kinds of symbiotic genes existed, corresponding to Mesorhizobium and Rhizobium, respectively. Available phosphorous (P) and potassium (K) contents were the main soil factors correlated with the distribution of these rhizobia in the sampling regions. Positive correlations between the available higher P content/lower K content and the dominance of Mesorhizobium species (M. temperatum, M. amorphae and M. septentrionale), and between the lower P content/higher K content and the dominance of R. yanglingense were found.

Growth stimulation of iodide-oxidizing α-Proteobacteria in iodide-rich environments.

α-Proteobacteria that can oxidize iodide (I(-)) to molecular iodine (I(2)) have only been isolated from iodide-rich natural and artificial environments, i.e., natural gas brine waters and seawaters supplemented with iodide, respectively. To understand the growth characteristics of such iodide-oxidizing bacteria (IOB) under iodide-rich environments, microcosms comprising natural seawater and 1 mM iodide were prepared, and the succession of microbial communities was monitored by culture-independent techniques. PCR-denaturing gradient gel electrophoresis and 16S rRNA gene sequence analysis showed that bacteria closely related with known IOB were predominant in the microcosms after several weeks of incubation. Quantitative PCR analysis targeting specific 16S rRNA gene regions of IOB showed that the relative abundance of IOB in the microcosms was 6-76% of the total bacterial population, whereas that in natural seawater was less than 1%. When 10(3) cells mL(-1) of IOB were inoculated into natural seawater supplemented with 0.1-1 mM iodide, significant growth (cell densities, 10(5)-10(6) cells mL(-1)) and I(2) production (6-32 µM) were observed. Interestingly, similar growth stimulation occurred when 12-44 µM of I(2) was added to seawater, instead of iodide. IOB were found to be more I(2) tolerant than the other heterotrophic bacteria in seawater. These results suggest that I(2) plays a key role in the growth stimulation of IOB in seawater. IOB could potentially attack other bacteria with I(2) to occupy their ecological niche in iodide-rich environments.

Complete genome sequence of Polymorphum gilvum SL003B-26A1T, a crude oil-degrading bacterium from oil-polluted saline soil.

Polymorphum gilvum SL003B-26A1(T) is a type strain of a newly published novel species in the novel genus Polymorphum. It was isolated from a crude oil-polluted saline soil in Shengli Oilfield, China, and was able to use the crude oil as the sole carbon source. Here we report the complete genome of SL003B-26A1(T) and the genes likely to be involved in oil degradation and ecological adaption.

Breoghania corrubedonensis gen. nov. sp. nov., a novel alphaproteobacterium isolated from a Galician beach (NW Spain) after the Prestige fuel oil spill, and emended description of the family Cohaesibacteraceae and the species Cohaesibacter gelatinilyticus.

A Gram-negative bacterium designated UBF-P1(T) was isolated from an enrichment culture established in nutrient supplemented artificial sea water with pyrene as a carbon source, and inoculated with a marine fuel oil-degrading consortium obtained from a sand sample collected from the beach of Corrubedo (A Coruña, Galicia, Spain) after the Prestige accidental oil spill. Phylogenetic analysis based on the almost complete 16S rRNA gene sequence affiliated strain UBF-P1(T) with the family Cohaesibacteraceae, Cohaesibacter gelatinilyticus (DSM 18289(T)) being the closest relative species with 92% sequence similarity. Cells were irregular rods, motile, strictly aerobic, catalase and oxidase positive. Ubiquinone 10 was the major respiratory lipoquinone. The major polar lipids comprised diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphatidylethanolamine (PE), phosphatidylmonomethylethanolamine (PME), and phosphatidylcholine (PC). The major fatty acids detected were C(18:1)ω7c, C(19:0) cycloω8c, and C(16:0). The G+C content of strain UBF-P1(T) was 63.9 mol%. The taxonomic comparison with the closest relative based on genotypic, phenotypic and chemotaxonomic characteristics supported that strain UBF-P1(T) could be classified as a novel genus and species, for which the name Breoghania corrubedonensis gen. nov., sp. nov. is proposed. The type strain of this new taxon is UBF-P1(T) (CECT 7622, LMG 25482, DSM 23382).

Characterization of strains unlike Mesorhizobium loti that nodulate lotus spp. in saline soils of Granada, Spain.

Lotus species are forage legumes with potential as pastures in low-fertility and environmentally constrained soils, owing to their high persistence and yield under those conditions. The aim of this work was the characterization of phenetic and genetic diversity of salt-tolerant bacteria able to establish efficient symbiosis with Lotus spp. A total of 180 isolates able to nodulate Lotus corniculatus and Lotus tenuis from two locations in Granada, Spain, were characterized. Molecular identification of the isolates was performed by repetitive extragenic palindromic PCR (REP-PCR) and 16S rRNA, atpD, and recA gene sequence analyses, showing the presence of bacteria related to different species of the genus Mesorhizobium: Mesorhizobium tarimense/Mesorhizobium tianshanense, Mesorhizobium chacoense/Mesorhizobium albiziae, and the recently described species, Mesorhizobium alhagi. No Mesorhizobium loti-like bacteria were found, although most isolates carried nodC and nifH symbiotic genes closely related to those of M. loti, considered the type species of bacteria nodulating Lotus, and other Lotus rhizobia. A significant portion of the isolates showed both high salt tolerance and good symbiotic performance with L. corniculatus, and many behaved like salt-dependent bacteria, showing faster growth and better symbiotic performance when media were supplemented with Na or Ca salts.

Robinia pseudoacacia in Poland and Japan is nodulated by Mesorhizobium amorphae strains.

Robinia pseudoacacia microsymbionts from plants growing in Poland and Japan were evaluated for phylogeny and taxonomic position by genomic approach. Based on the comparative analyses of atpD (368 bp) and dnaK (573 bp) gene sequences as well as 16S rDNA restriction analysis (RFLP-16S rDNA), R. pseudoacacia microsymbionts were identified as Mesorhizobium strains. In dnaK and atpD gene phylograms R. pseudoacacia nodulators formed robust, monophyletic clusters with Mesorhizobium species with the nucleotide sequence similarity of 91-98% and 90-98%, respectively. The classification of R. pseudoacacia rhizobia to the genus Mesorhizobium was also supported by amplified 16S rDNA restriction analysis. The studied bacteria formed common clusters with Mesorhizobium species, and their DNA patterns were identical or nearly identical to Mesorhizobium genus strains. When DNA-DNA hybridization was performed, the total DNA of the representative R. pseudoacacia rhizobia exhibited 51-75% relatedness to DNA of Mesorhizobium amorphae ICMP15022 strain and below 41% to DNA of other Mesorhizobium species. These results showed that R. pseudoacacia and M. amorphae belong to the same genomospecies. The G+C content of DNA of R. pseudoacacia two microsymbionts was 59.7 and 60.6 mol% compared to 61-64 mol% across M. amorphae strains.

Mesorhizobium robiniae sp. nov., isolated from root nodules of Robinia pseudoacacia.

Previously, five rhizobial strains isolated from root nodules of Robinia pseudoacacia were assigned to the same genospecies on the basis of identical 16S rRNA gene sequences and phylogenetic analyses of the nodA, nodC and nifH genes, in which the five isolates formed a well-supported group that excluded other sequences found in public databases. In this study, the 16S rRNA gene sequence similarities between the isolates and Mesorhizobium mediterraneum UPM-Ca36(T) and Mesorhizobium temperatum SDW018(T) were 99.5 and 99.6 %, respectively. The five isolates were also different from defined Mesorhizobium species using ERIC fingerprint profiles and they formed a novel Mesorhizobium lineage in phylogenetic analyses of recA and atpD gene sequences. DNA-DNA relatedness values between the representative strain, CCNWYC 115(T), and type strains of defined Mesorhizobium species were found to be lower than 47.5 %. These results indicated that the isolates represented a novel genomic species. Therefore, a novel species, Mesorhizobium robiniae sp. nov., is proposed, with type strain CCNWYC 115(T) (=ACCC 14543(T) =HAMBI 3082(T)). Strain CCNWYC 115(T) can form effective nodules only on its original host.