Multilocus sequence analysis of Ensifer and related taxa

Multilocus sequence typing provides insights into the population structure and evolutionary potential of Brenneria goodwinii, associated with acute oak decline

Brenneria goodwinii is one of the most frequently isolated Gram-negative bacteria from native oak species, Quercus robur and Q. petraea, affected by acute oak decline (AOD) in the UK. We investigated the population biology of this bacterial species using a multilocus sequence analysis to determine the population structure and evolutionary potential. Seven partial housekeeping genes were used in the analyses. Amongst 44 bacterial strains from seven different locations, we identified 22 unique sequence types [STs]; only one ST was found at two separate locations. Phylogenetic and cluster-based analyses suggested that B. goodwinii STs form two main distinct groups; however, no geographical pattern of their distribution could be observed. Clonality and recombination tests demonstrated that the studied population is primarily clonal, however both mutation and recombination processes play a role in shaping the genetic structure and evolution of the population. Our study suggests that the B. goodwinii population on oak in the UK has an endemic form, with background recombination appearing to generate new alleles more frequently than mutation, despite the introduction of nucleotide substitutions being approximately twice less likely than mutation. The newly emerged STs subsequently undergo clonal expansion to become dominant genotypes within their specific geographical locations and even within the individual host oak trees.

Biogeography of a Novel Ensifer meliloti Clade Associated with the Australian Legume Trigonella suavissima

Here, we describe a novel clade within Ensifer meliloti and consider how geographic and ecological isolation contributed to the limited distribution of this group. Members of the genus Ensifer are best known for their ability to form nitrogen-fixing symbioses with forage legumes of three related genera, Medicago L., Melilotus Mill., and Trigonella L., which are members of the tribe Trifolieae. These legumes have a natural distribution extending from the Mediterranean Basin through western Asia, where there is an unsurpassed number of species belonging to these genera. Trigonella suavissima L. is unusual in that it is the only species in the tribe Trifolieae that is native to Australia. We compared the genetic diversity and taxonomic placement of rhizobia nodulating T. suavissima with those of members of an Ensifer reference collection. Our goal was to determine if the T. suavissima rhizobial strains, like their plant host, are naturally limited to the Australian continent. We used multilocus sequence analysis to estimate the genetic relatedness of 56 T. suavissima symbionts to 28 Ensifer reference strains. Sequence data were partitioned according to the replicons in which the loci are located. The results were used to construct replicon-specific phylogenetic trees. In both the chromosomal and chromid trees, the Australian strains formed a distinct clade within E. meliloti The strains also shared few alleles with Ensifer reference strains from other continents. Carbon source utilization assays revealed that the strains are also unusual in their ability to utilize 2-oxoglutarate as a sole carbon source. A strategy was outlined for locating similar strains elsewhere.IMPORTANCE In this study, we employed a biogeographical approach to investigate the origins of a symbiotic relationship between an Australian legume and its nitrogen-fixing rhizobia. The question of the ancestral origins of these symbionts is based on the observation that the legume host is not closely related to other native Australian legumes. Previous research has shown that the legume host Trigonella suavissima is instead closely related to legumes native to the Mediterranean Basin and western Asia, suggesting that it may have been introduced in Australia from those regions. This led to the question of whether its rhizobia may have been introduced as well. In this study, we were unable to find persuasive evidence supporting this hypothesis. Instead, our results suggest either that the T. suavissima rhizobia are native to Australia or that our methods for locating their close relatives elsewhere are inadequate. A strategy to investigate the latter alternative is proposed.

Rhizobium oryziradicis sp. nov., isolated from rice roots

Two Gram-stain-negative, aerobic, rod-shaped endophytic bacterial strains, N19T and N11-2, were isolated from fresh rice (Oryza sativa) roots during investigation of the rice endophytic bacterial diversity. The 16S rRNA gene sequence results indicated that the similarity between strains N19T and N11-2 was 100 %. Both of them belong to the genus Rhizobium, with close similarity to Rhizobium taibaishanense CCNWSX 0483T (97.7 %), followed by Rhizobium vitis NCPPB 3554T (97.5 %). The sequence similarities of the housekeeping genes recA, gyrB and glnA between the novel isolates and members of the established species of the genus Rhizobium were less than 87 %. The DNA-DNA hybridization rates between strains N19T and N11-2 were 87.9 % using the initial renaturation rate method. Based on draft genome sequences, strain N19T showed 18.2 % and 19.6 % DNA-DNA hybridization values to R. taibaishanense CCNWSX 0483T and R. vitis S4, which demonstrated that these new isolates represent a novel species in the genus Rhizobium. The main cellular fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c). The DNA G+C content of strain N19T was 58.7 mol% (Tm). The polar lipid profile of N19T consisted of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, an unknown lipid, two unknown aminolipids and an unidentified aminophospholipid. According to physiological and biochemical characteristics and genotypic data, strains N19T and N11-2 are considered to represent a novel species of the genus Rhizobium, for which the name Rhizobium oryziradicis sp. nov. is proposed, with N19T (=ACCC 19962T=KCTC 52413T) as the type strain.

Differential colonization by bioprospected rhizobial bacteria associated with common bean in different cropping systems

In this study, we evaluated the diversity of rhizobia isolated from root nodules on common bean (Phaseolus vulgaris) derived from Andean and Mesoamerican centers and grown under field and greenhouse conditions. Genetic characterization of isolates was performed by sequencing analyses of the 16S rRNA gene and 2 housekeeping genes, recA and glnII, and by the amplification of nifH. Symbiotic efficiency was evaluated by examining nodulation, plant biomass production, and plant nitrogen (N) accumulation. The influence of the environment was observed in nodulation capacity, where Rhizobium miluonense was dominant under greenhouse conditions and the Rhizobium acidisoli group prevailed under field conditions. However, strain LGMB41 fit into a separate group from the type strain of R. acidisoli in terms of multilocus phylogeny, implying that it could belong to a new species. Rhizobium miluonense LGMB73 showed the best symbiotic efficiency performance, i.e., with the highest shoot-N content (77.7 mg/plant), superior to the commercial standard strain (56.9 mg/plant). Biodiversity- and bioprospecting-associated studies are important to better understand ecosystems and to develop more effective strategies to improve plant growth using a N-fixation process.

Ensifer shofinae sp. nov., a novel rhizobial species isolated from root nodules of soybean (Glycine max)

Two bacterial strains isolated from root nodules of soybean were characterized phylogenetically as members of a distinct group in the genus Ensifer based on 16S rRNA gene comparisons. They were also verified as a separated group by the concatenated sequence analyses of recA, atpD and glnII (with similarities ≤93.9% to the type strains for defined species), and by the average nucleotide identities (ANI) between the whole genome sequence of the representative strain CCBAU 251167T and those of the closely related strains in Ensifer glycinis and Ensifer fredii (90.5% and 90.3%, respectively). Phylogeny of symbiotic genes (nodC and nifH) grouped these two strains together with some soybean-nodulating strains of E. fredii, E. glycinis and Ensifer sojae. Nodulation tests indicated that the representative strain CCBAU 251167T could form root nodules with capability of nitrogen fixing on its host plant and Glycine soja, Cajanus cajan, Vigna unguiculata, Phaseolus vulgaris and Astragalus membranaceus, and it formed ineffective nodules on Leucaena leucocephala. Strain CCBAU 251167T contained fatty acids 18:1 ω9c, 18:0 iso and 20:0, differing from other related strains. Utilization of l-threonine and d-serine as carbon source, growth at pH 6.0 and intolerance of 1% (w/v) NaCl distinguished strain CCBAU 251167T from other type strains of the related species. The genome size of CCBAU 251167T was 6.2Mbp, comprising 7,581 predicted genes with DNA G+C content of 59.9mol% and 970 unique genes. Therefore, a novel species, Ensifer shofinae sp. nov., is proposed, with CCBAU 251167T (=ACCC 19939T=LMG 29645T) as type strain.

Specificity in Legume-Rhizobia Symbioses

Most species in the Leguminosae (legume family) can fix atmospheric nitrogen (N₂) via symbiotic bacteria (rhizobia) in root nodules. Here, the literature on legume-rhizobia symbioses in field soils was reviewed and genotypically characterised rhizobia related to the taxonomy of the legumes from which they were isolated. The Leguminosae was divided into three sub-families, the Caesalpinioideae, Mimosoideae and Papilionoideae. Bradyrhizobium spp. were the exclusive rhizobial symbionts of species in the Caesalpinioideae, but data are limited. Generally, a range of rhizobia genera nodulated legume species across the two Mimosoideae tribes Ingeae and Mimoseae, but Mimosa spp. show specificity towards Burkholderia in central and southern Brazil, Rhizobium/Ensifer in central Mexico and Cupriavidus in southern Uruguay. These specific symbioses are likely to be at least in part related to the relative occurrence of the potential symbionts in soils of the different regions. Generally, Papilionoideae species were promiscuous in relation to rhizobial symbionts, but specificity for rhizobial genus appears to hold at the tribe level for the Fabeae (Rhizobium), the genus level for Cytisus (Bradyrhizobium), Lupinus (Bradyrhizobium) and the New Zealand native Sophora spp. (Mesorhizobium) and species level for Cicer arietinum (Mesorhizobium), Listia bainesii (Methylobacterium) and Listia angolensis (Microvirga). Specificity for rhizobial species/symbiovar appears to hold for Galega officinalis (Neorhizobium galegeae sv. officinalis), Galega orientalis (Neorhizobium galegeae sv. orientalis), Hedysarum coronarium (Rhizobium sullae), Medicago laciniata (Ensifer meliloti sv. medicaginis), Medicago rigiduloides (Ensifer meliloti sv. rigiduloides) and Trifolium ambiguum (Rhizobium leguminosarum sv. trifolii). Lateral gene transfer of specific symbiosis genes within rhizobial genera is an important mechanism allowing legumes to form symbioses with rhizobia adapted to particular soils. Strain-specific legume rhizobia symbioses can develop in particular habitats.

Phylogenetically diverse group of native bacterial symbionts isolated from root nodules of groundnut (Arachis hypogaea L.) in South Africa

Groundnut is an economically important N_​2-fixing legume that can contribute about 100–190 kg N ha⁻¹ to cropping systems. In this study, groundnut-nodulating native rhizobia in South African soils were isolated from root nodules. Genetic analysis of isolates was done using restriction fragment length polymorphism (RFLP)-PCR of the intergenic spacer (IGS) region of 16S-23S rDNA. A total of 26 IGS types were detected with band sizes ranging from 471 to 1415 bp. The rhizobial isolates were grouped into five main clusters with Jaccard's similarity coefficient of 0.00–1.00, and 35 restriction types in a UPGMA dendrogram. Partial sequence analysis of the 16S rDNA, IGS of 16S rDNA-23S rDNA, atpD, gyrB, gltA, glnII and symbiotic nifH and nodC genes obtained for representative isolates of each RFLP-cluster showed that these native groundnut-nodulating rhizobia were phylogenetically diverse, thus confirming the extent of promiscuity of this legume. Concatenated gene sequence analysis showed that most isolates did not align with known type strains, and may represent new species from South Africa. This underscored the high genetic variability associated with groundnut Rhizobium and Bradyrhizobium in South African soils, and the possible presence of a reservoir of novel groundnut-nodulating Bradyrhizobium and Rhizobium in the country.

The evolution of symbiont preference traits in the model legume Medicago truncatula

Many hosts preferentially associate with or reward better symbionts, but how these symbiont preference traits evolve is an open question. Legumes often form more nodules with or provide more resources to rhizobia that fix more nitrogen (N), but they also acquire N from soil via root foraging. It is unclear whether root responses to abiotically and symbiotically derived N evolve independently. Here, we measured root foraging and both preferential allocation of root resources to and preferential association with an effective vs an ineffective N-fixing Ensifer meliloti strain in 35 inbred lines of the model legume Medicago truncatula. We found that M. truncatula is an efficient root forager and forms more nodules with the effective rhizobium; root biomass increases with the number of effective, but not ineffective, nodules, indicating preferential allocation to roots harbouring effective rhizobia; root foraging is not genetically correlated with either preferential allocation or association; and selection favours plant genotypes that form more effective nodules. Root foraging and symbiont preference traits appear to be genetically uncoupled in M. truncatula. Rather than evolving to exclude ineffective partners, our results suggest that preference traits probably evolve to take better advantage of effective symbionts.

Rhizobium rhizosphaerae sp. nov., a novel species isolated from rice rhizosphere

Two novel, Gram-negative, motile, rod-shaped, aerobic bacterial strains, MH17^T and RD15, were isolated from the sterilized root and rhizosphere soil of rice, respectively. Phylogenetic analysis based on 16S rRNA gene sequences showed that the similarity between strains MH17^T and RD15 was 100%. The isolates exhibit high sequence similarities to Rhizobium oryzae CGMCC 1.7048^T (98.7%) and Rhizobium petrolearium SL-1^T (97.0% and 97.1%), which supports that they belong to a novel species in the genus Rhizobium. Strains MH17^T and RD15 exhibited growth at 15-45 °C, pH 5.0-11.0, 0-2.0% sodium chloride (w/v). Sequence analysis of housekeeping genes gyrB, recA, atpD, ropB, gltA showed that these two novel strains had less than 94% similarity with the known species, indicating the distinct position of MH17^T and RD15 in the genus Rhizobium. The major cellular fatty acids were identified as summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c). Type strain MH17^T had 87.5% DNA-DNA relatedness with RD15 by using the initial renaturation rate method. Based on draft genome sequences, strain MH17^T showed 30.1% DNA-DNA hybridization values to R. oryzae CGMCC 1.7048^T, the closely related strain, which supported that MH17^T represents a novel species in the genus Rhizobium. Average nucleotide identity (ANI) between strains MH17^T and RD15 were 97.8%, and strain MH17^T showed 82.2% ANI value with R. oryzae CGMCC 1.7048^T. The DNA G+C content was 60.4 mol% (T_m). Based on physiological, biochemical characteristic, genotypic data, strains MH17^T and RD15 are concluded to represent a new species within the genus Rhizobium, for which the name Rhizobium rhizosphaerae sp. nov. is proposed. The type strain is MH17^T (=ACCC 19963^T = KCTC 52414^T).

Diverse Mesorhizobium bacteria nodulate native Astragalus and Oxytropis in arctic and subarctic areas in Eurasia

Rhizobia nodulating native Astragalus and Oxytropis spp. in Northern Europe are not well-studied. In this study, we isolated bacteria from nodules of four Astragalus spp. and two Oxytropis spp. from the arctic and subarctic regions of Sweden and Russia. The phylogenetic analyses were performed by using sequences of three housekeeping genes (16S rRNA, rpoB and recA) and two accessory genes (nodC and nifH). The results of our multilocus sequence analysis (MLSA) of the three housekeeping genes tree showed that all the 13 isolates belonged to the genus Mesorhizobium and were positioned in six clades. Our concatenated housekeeping gene tree also suggested that the isolates nodulating Astragalus inopinatus, Astragalus frigidus, Astragalus alpinus ssp. alpinus and Oxytropis revoluta might be designated as four new Mesorhizobium species. The 13 isolates were grouped in three clades in the nodC and nifH trees. ¹⁵N analysis suggested that the legumes in association with these isolates were actively fixing nitrogen.

Presence of diverse rhizobial communities responsible for nodulation of common bean (Phaseolus vulgaris) in South African and Mozambican soils

The diversity and phylogeny of root-nodule bacteria isolated from common bean grown in Mozambique and different provinces of South Africa was studied by restriction fragment length polymorphism (RFLP) and phylogenetic analysis. The combined restriction banding pattern of 16S rRNA and nifH profile-generated dendrogram grouped all test isolates into four major clusters with XXI restriction groups and three clusters with VIII restriction groups. Location-based clustering was observed with the 16S rRNA RFLP analysis. Phylogenetic analysis of 16S rRNA, glnII, gyrB and gltA sequences showed that common bean was nodulated specifically by Rhizobium etli in Mozambican soils, and by a diverse group of Rhizobium species in South African soils (e.g. R. etli, R. phaseoli, R. sophoriradicis, R. leucaenae and novel group of Rhizobium spp.). Isolates from the Eastern Cape region of South Africa were dominated by R. leucaenae Overall, the results suggested high nodulation promiscuity of common bean grown in Southern Africa. The nifH and nodC sequence analysis classified all the test isolates with R. etli group, except for isolates TUTPVSA117, TUTPVSA114 and TUTPVSA110 which delineated with R. tropici group. This finding was inconsistent with the phylogram of the housekeeping genes, and is probably an indication of horizontal gene transfer among the Rhizobium isolates tested.

Chelatococcus thermostellatus sp. nov., a new thermophile for bioplastic synthesis: comparative phylogenetic and physiological study

The poly(3-hydroxybutyrate), PHB, accumulating thermophilic strain MW9^T, isolated from an aerobic organic waste treatment plant, was characterized by detailed physiological and phylogenetic studies. The strain is a Gram-stain-negative, rod shaped, non-spore forming member of Alphaproteobacteria. It shows optimum growth at 50 °C. Based on 16S rRNA gene sequence similarity, the strain together with five very similar isolates, was affiliated to the genus Chelatococcus (Ibrahim et al. in J Appl Microbiol 109:1579–1590, 2010). Rep-PCR genomic fingerprints and partial dnaK gene sequence also revealed that these isolates are very similar, but differ from other Chelatococcus type strains. The major fatty acids were similar to those of other strains of the genus Chelatococcus. DNA–DNA hybridization of strain MW9^T with Chelatococcus species type strains revealed 11.0–47.7 % relatedness. G+C content of DNA was 67.1 mol%, which is comparable with the other strains of Chelatococcus species. The physiological and phenotypic characteristics of the new strain MW9^T are sufficient to differentiate it from previously described species in the genus Chelatococcus. Strain MW9^T is considered to represent a novel species of the genus Chelatococcus, for which the name Chelatococcus thermostellatus is proposed. The type strain is MW9^T (=LMG 27009^T = DSM 28244^T). Compared to known Chelatococcus strains, strain MW9^T could be a potent candidate for bioplastic production at elevated temperature.

Rhizobium albus sp. nov., Isolated from Lake Water in Xiamen, Fujian Province of China

A Gram-stain-negative, aerobic bacterial strain, designated Y21^T, was isolated from surface lake water in Xiamen, Fujian Province of China. Growth was observed at temperatures from 4 to 37 °C, at salinities from 0 to 7.0 % and at pH from 6.0 to 10.0. Optimum growth was observed at 28 °C, at pH 7.0 and with 1.5-2.0 % (w/v) NaCl. The highest similarity of 16S rRNA gene sequence between strain Y21^T and the other strains was 96.9 %. Phylogenetic analysis based on 16S rRNA gene sequencing revealed that the strain was a member of the genus Rhizobium, forming a distinct lineage with R. subbaraonis KCTC 23614^T. The dominant fatty acids were summed feature 8 (comprising C_18:1 ω7c and/or C_18:1 ω6c), C_18:1 ω7c 11-methyl, which accounted for 78.1 %. The G+C content of the chromosomal DNA was 60.9 mol%. The predominant respiratory quinone was ubiquinone-10. The polar lipids of strain Y21^T were found to consist of five unidentified phospholipids and three unidentified aminolipids. According to its morphology, physiology, fatty acid composition and 16S rRNA sequence data, strain Y21^T should be regarded as a new species of the genus Rhizobium, for which Rhizobium albus sp. nov. is proposed (type strain Y21^T = MCCC 1F01210^T = KCTC 42252^T).

Phylogenetic Diversity of Ammopiptanthus Rhizobia and Distribution of Rhizobia Associated with Ammopiptanthus mongolicus in Diverse Regions of Northwest China

Aiming to investigate the diversity and distribution of rhizobia associated with Ammopiptanthus, an endangered evergreen legume widely distributed in deserts, we characterized a total of 219 nodule isolates from nine sampling sites in Northwest China with different soil characteristics based upon restriction fragment length polymorphism (RFLP) analysis of 16S ribosomal RNA (rRNA) and symbiotic genes (nodC and nifH). Ten isolates representing different 16S rRNA-RFLP types were selected for further sequence analyses of 16S rRNA and four housekeeping genes. As results, nine genospecies belonging to the genera Ensifer, Neorhizobium, Agrobacterium, Pararhizobium, and Rhizobium could be defined among the isolates. The nodC and nifH phylogenies of 14 isolates representing different symbiotic-RFLP types revealed five lineages linked to Ensifer fredii, Ensifer meliloti, Rhizobium leguminosarum, Mesorhizobium amorphae, and Rhizobium gallicum, which demonstrated the various origins and lateral transfers of symbiotic genes between different genera and species. The rhizobial diversities of Ammopiptanthus mongolicus varied among regions, and the community compositions of rhizobia associated with A. mongolicus were significantly different in wild and cultured fields. Constrained correspondence analysis showed that the distribution of A. mongolicus rhizobia could be explained by available potassium content and that the assembly of symbiotic types was mainly affected by available phosphorus content and carbon-nitrogen ratio.

Rhizobium leguminosarum symbiovar trifolii, Ensifer numidicus and Mesorhizobium amorphae symbiovar ciceri (or Mesorhizobium loti) are new endosymbiotic bacteria of Lens culinaris Medik

A total of 142 rhizobial bacteria were isolated from root nodules of Lens culinaris Medik endemic to Tunisia and they belonged to the species Rhizobium leguminosarum, and for the first time to Ensifer and Mesorhizobium, genera never previously described as microsymbionts of lentil. Phenotypically, our results indicate that L. culinaris Medik strains showed heterogenic responses to the different phenotypic features and they effectively nodulated their original host. Based on the concatenation of the 16S rRNA with relevant housekeeping genes (glnA, recA, dnaK), rhizobia that nodulate lentil belonged almost exclusively to the known R. leguminosarum sv. viciae. Interestingly, R. leguminosarum sv. trifolii, Ensifer numidicus (10 isolates) and Mesorhizobium amorphae (or M. loti) (9 isolates) isolates species, not considered, up to now, as a natural symbiont of lentil are reported. The E. numidicus and M. amorphae (or M. loti) strains induced fixing nodules on Medicago sativa and Cicer arietinum host plants, respectively. Symbiotic gene phylogenies showed that the E. numidicus, new symbiont of lentil, markedly diverged from strains of R. leguminosarum, the usual symbionts of lentil, and converged to the symbiovar meliloti so far described within E. meliloti Indeed, the nodC and nodA genes from the M. amorphae showed more than 99% similarity with respect to those from M. mediterraneum, the common chickpea nodulating species, and would be included in the new infrasubspecific division named M. amorphae symbiovar ciceri, or to M. loti, related to the strains able to effectively nodulate C. arietinum host plant. On the basis of these data, R. leguminosarum sv. trifolii (type strain LBg3 (T)), M. loti or M. amorphae sv. ciceri (type strain LB4 (T)) and E. numidicus (type strain LBi2 (T)) are proposed as new symbionts of L. culinaris Medik.

Identification of symbiotic nitrogen-fixing bacteria from three African leguminous trees in Gorongosa National Park

The symbiosis between leguminous plants and symbiotic nitrogen-fixing bacteria is a key component of terrestrial ecosystems. Woody legumes are well represented in tropical African forests but despite their ecological and socio-economic importance, they have been little studied for this symbiosis. In this study, we examined the identity and diversity of symbiotic-nitrogen fixing bacteria associated with Acacia xanthophloea, Faidherbia albida and Albizia versicolor in the Gorongosa National Park (GNP) in Mozambique. To the best of our knowledge, this is the first report on the identity of symbiotic-nitrogen fixing bacteria in this region. 166 isolates were obtained and subjected to molecular identification. BOX-A1R PCR was used to discriminate different bacterial isolates and PCR-sequencing of 16S rDNA, and two housekeeping genes, glnII and recA, was used to identify the obtained bacteria. The gene nifH was also analyzed to assess the symbiotic capacity of the obtained bacteria. All isolates from F. albida and Al. versicolor belonged to the Bradyrhizobium genus whereas isolates from Ac. xanthophloea clustered with Mesorhizobium, Rhizobium or Ensifer strains. Soil chemical analysis revealed significant differences between the soils occupied by the three studied species. Thus, we found a clear delimitation in the rhizobial communities and soils associated with Ac. xanthophloea, F. albida and Al. versicolor, and higher rhizobial diversity for Ac. xanthophloea than previously reported.

Pararhizobium polonicum sp. nov. isolated from tumors on stone fruit rootstocks

Five Gram-negative, rod-shaped, non-spore-forming bacteria were isolated from galls on different stone fruit rootstocks in Poland: strains F5.1(T) and F5.3 from Prunus avium F12/1, strains CP3.5 and CP17.2.1 from Prunus avium and strain AL5.1.8 from Prunus cerasifera. On the basis of 16S rDNA phylogeny, the strains cluster together and belong to the genus Pararhizobium with type strain of Pararhizobium herbae (99.6-99.8%) as their closest relative. Phylogenetic analysis of the novel strains using housekeeping genes atpD, recA and rpoB revealed their distinct position separate from other known Rhizobium species and confirmed their relation to P. herbae. DNA-DNA hybridization of strains F5.1(T), with the type strain of P. herbae LMG 25718(T) and Pararhizobium giardinii R-4385(T) revealed 28.3% and 27.9% of DNA-DNA relatedness, respectively. Phenotypic and physiological properties differentiate the novel isolates from other closely related species. On the basis of the results obtained, the five isolates are considered to represent a novel species of the genus Pararhizobium, for which the name Pararhizobium polonicum sp. nov. (type strain F5.1(T)=LMG 28610(T)=CFBP 8359(T)) is proposed.

Genomic resources for identification of the minimal N2 -fixing symbiotic genome

The lack of an appropriate genomic platform has precluded the use of gain-of-function approaches to study the rhizobium-legume symbiosis, preventing the establishment of the genes necessary and sufficient for symbiotic nitrogen fixation (SNF) and potentially hindering synthetic biology approaches aimed at engineering this process. Here, we describe the development of an appropriate system by reverse engineering Sinorhizobium meliloti. Using a novel in vivo cloning procedure, the engA-tRNA-rmlC (ETR) region, essential for cell viability and symbiosis, was transferred from Sinorhizobium fredii to the ancestral location on the S. meliloti chromosome, rendering the ETR region on pSymB redundant. A derivative of this strain lacking both the large symbiotic replicons (pSymA and pSymB) was constructed. Transfer of pSymA and pSymB back into this strain restored symbiotic capabilities with alfalfa. To delineate the location of the single-copy genes essential for SNF on these replicons, we screened a S. meliloti deletion library, representing > 95% of the 2900 genes of the symbiotic replicons, for their phenotypes with alfalfa. Only four loci, accounting for < 12% of pSymA and pSymB, were essential for SNF. These regions will serve as our preliminary target of the minimal set of horizontally acquired genes necessary and sufficient for SNF.

Phylogenetic analysis and serotyping of Vibrio splendidus-related bacteria isolated from salmon farm cleaner fish

Cleaner fish, i.e. various wrasse (Labridae) species and lumpsucker Cyclopterus lumpus, are to an increasing extent used for biocontrol of the salmon louse Lepeophtheirus salmonis in European salmon farming. Although efficient de-licers, cleaner fish mortality levels in salmon farms are often high. Bacterial infections are common, and Vibrio splendidus-related strains are frequently identified during diagnostic investigations. The population structure of 112 V. splendidus-related isolates, derived primarily from wrasse species, was investigated by means of multilocus sequence analysis using 5 housekeeping genes (rpoD, ftsZ, pyrH, rpoA and atpA). Most isolates were found to be closely related to the V. splendidus type strain, yet displayed extensive genetic microdiversity. Slide agglutination testing using polyclonal rabbit antisera further indicated O-antigen variability. Intra-outbreak genetic and antigenic diversity suggests direct infection from seawater, rather than fish-to-fish transmission, as the main route of infection. The variable nature of isolates involved complicates qualified selection of representative candidate strains, e.g. for infection and vaccine trials.

Phylogenetic diversity on housekeeping and symbiotic genes of rhizobial from Sphaerophysa in China

This study explored the diversity and phylogeny of rhizobia collected from nodules of Sphaerophysa salsula in different geographical regions of Northwest China. The 16S rRNA gene sequences divided the strains into the following distinct groups: Mesorhizobium, Rhizobium and Shinella. The phylogenies of recA and atpD genes showed low correlation with nifH and nodA gene in most species, which indicated that, the gene recombination between species and genera might have been exist. To our knowledge, this is the first study using the multilocus sequencing analysis Sphaerophysa rhizobia in order to understand the relation between genetic diversity and ecology.

Average nucleotide identity of genome sequences supports the description of Rhizobium lentis sp. nov., Rhizobium bangladeshense sp. nov. and Rhizobium binae sp. nov. from lentil (Lens culinaris) nodules

Rhizobial strains isolated from effective root nodules of field-grown lentil (Lens culinaris) from different parts of Bangladesh were previously analysed using sequences of the 16S rRNA gene, three housekeeping genes (recA, atpD and glnII) and three nodulation genes (nodA, nodC and nodD), DNA fingerprinting and phenotypic characterization. Analysis of housekeeping gene sequences and DNA fingerprints indicated that the strains belonged to three novel clades in the genus Rhizobium. In present study, a representative strain from each clade was further characterized by determination of cellular fatty acid compositions, carbon substrate utilization patterns and DNA-DNA hybridization and average nucleotide identity (ANI) analyses from whole-genome sequences. DNA-DNA hybridization showed 50-62% relatedness to their closest relatives (the type strains of Rhizobium etli and Rhizobium phaseoli) and 50-60% relatedness to each other. These results were further supported by ANI values, based on genome sequencing, which were 87-92% with their close relatives and 88-89% with each other. On the basis of these results, three novel species, Rhizobium lentis sp. nov. (type strain BLR27(T) = LMG 28441(T) = DSM 29286(T)), Rhizobium bangladeshense sp. nov. (type strain BLR175(T) = LMG 28442(T) = DSM 29287(T)) and Rhizobium binae sp. nov. (type strain BLR195(T) = LMG 28443(T) = DSM 29288(T)), are proposed. These species share common nodulation genes (nodA, nodC and nodD) that are similar to those of the symbiovar viciae.

Rhizobium oryzicola sp. nov., potential plant-growth-promoting endophytic bacteria isolated from rice roots

Bacterial strains ZYY136(T) and ZYY9 were isolated from surface-sterilized rice roots from a long-term experiment of rice-rice--Astragalus sinicus rotation. The 16S rRNA gene sequences of strains ZYY136(T) and ZYY9 showed the highest similarity, of 97.0%, to Rhizobium tarimense PL-41(T). Sequence analysis of the housekeeping genes recA, thrC and atpD clearly differentiated the isolates from currently described species of the genus Rhizobium. The DNA-DNA relatedness value between ZYY136(T) and ZYY9 was 82.3%, and ZYY136(T) showed 34.0% DNA-DNA relatedness with the most closely related type strain, R. tarimense PL-41(T). The DNA G+C content of strain ZYY136(T) was 58.1 mol%. The major cellular fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c), C16 : 0 and C16 : 0 3-OH. Strains ZYY136(T) and ZYY9 could be differentiated from the previously defined species of the genus Rhizobium by several phenotypic characteristics. Therefore, we conclude that strains ZYY136(T) and ZYY9 represent a novel species of the genus Rhizobium, for which the name Rhizobium oryzicola sp. nov. is proposed (type strain ZYY136(T) = ACCC 05753(T) = KCTC 32088(T)).

A database for the taxonomic and phylogenetic identification of the genus Bradyrhizobium using multilocus sequence analysis

Background

Biological nitrogen fixation, with an emphasis on the legume-rhizobia symbiosis, is a key process for agriculture and the environment, allowing the replacement of nitrogen fertilizers, reducing water pollution by nitrate as well as emission of greenhouse gases. Soils contain numerous strains belonging to the bacterial genus Bradyrhizobium, which establish symbioses with a variety of legumes. However, due to the high conservation of Bradyrhizobium 16S rRNA genes - considered as the backbone of the taxonomy of prokaryotes - few species have been delineated. The multilocus sequence analysis (MLSA) methodology, which includes analysis of housekeeping genes, has been shown to be promising and powerful for defining bacterial species, and, in this study, it was applied to Bradyrhizobium, species, increasing our understanding of the diversity of nitrogen-fixing bacteria.

Description

Classification of bacteria of agronomic importance is relevant to biodiversity, as well as to biotechnological manipulation to improve agricultural productivity. We propose the construction of an online database that will provide information and tools using MLSA to improve phylogenetic and taxonomic characterization of Bradyrhizobium, allowing the comparison of genomic sequences with those of type and representative strains of each species.

Conclusion

A database for the taxonomic and phylogenetic identification of the Bradyrhizobium, genus, using MLSA, will facilitate the use of biological data available through an intuitive web interface. Sequences stored in the on-line database can be compared with multiple sequences of other strains with simplicity and agility through multiple alignment algorithms and computational routines integrated into the database. The proposed database and software tools are available at http://mlsa.cnpso.embrapa.br, and can be used, free of charge, by researchers worldwide to classify Bradyrhizobium, strains; the database and software can be applied to replicate the experiments presented in this study as well as to generate new experiments. The next step will be expansion of the database to include other rhizobial species.

Multilocus sequence analysis (MLSA) in prokaryotic taxonomy

To obtain a higher resolution of the phylogenetic relationships of species within a genus or genera within a family, multilocus sequence analysis (MLSA) is currently a widely used method. In MLSA studies, partial sequences of genes coding for proteins with conserved functions ('housekeeping genes') are used to generate phylogenetic trees and subsequently deduce phylogenies. However, MLSA is not only suggested as a phylogenetic tool to support and clarify the resolution of bacterial species with a higher resolution, as in 16S rRNA gene-based studies, but has also been discussed as a replacement for DNA-DNA hybridization (DDH) in species delineation. Nevertheless, despite the fact that MLSA has become an accepted and widely used method in prokaryotic taxonomy, no common generally accepted recommendations have been devised to date for either the whole area of microbial taxonomy or for taxa-specific applications of individual MLSA schemes. The different ways MLSA is performed can vary greatly for the selection of genes, their number, and the calculation method used when comparing the sequences obtained. Here, we provide an overview of the historical development of MLSA and critically review its current application in prokaryotic taxonomy by highlighting the advantages and disadvantages of the method's numerous variations. This provides a perspective for its future use in forthcoming genome-based genotypic taxonomic analyses.

Tatumella saanichensis sp. nov., isolated from a cystic fibrosis patient

Polyphasic taxonomic analysis was performed on a clinical isolate (NML 06-3099T) from a cystic fibrosis patient, including whole-genome sequencing, proteomics, phenotypic testing, electron microscopy, chemotaxonomy and a clinical investigation. Comparative whole-genome sequence analysis and multilocus sequence analysis (MLSA) between Tatumella ptyseos ATCC 33301T and clinical isolate NML 06-3099T suggested that the clinical isolate was closely related to, but distinct from, the species T. ptyseos. By 16S rRNA gene sequencing, the clinical isolate shared 98.7 % sequence identity with T. ptyseos ATCC 33301T. A concatenate of six MLSA loci (totalling 4500 bp) revealed < 93.9 % identity between T. ptyseos ATCC 33301T, other members of the genus and the clinical isolate. A whole-genome sequence comparison between NML 06-3099T and ATCC 33301T determined that the average nucleotide identity was 76.24 %. The overall DNA G+C content of NML 06-3099T was 51.27 %, consistent with members of the genus Tatumella. By matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS analysis, NML 06-3099T had a genus-level match, but not a species-level match, to T. ptyseos. By shotgun proteomics, T. ptyseos ATCC 33301T and NML 06-3099T were found to have unique proteomes. The two strains had similar morphologies and multiple fimbriae, as observed by transmission electron microscopy, but were distinguishable by phenotypic testing. Cellular fatty acids found were typical for members of the Enterobacteriaceae. NML 06-3099T was susceptible to commonly used antibiotics. Based on these data, NML 06-3099T represents a novel species in the genus Tatumella, for which the name Tatumella saanichensis sp. nov. is proposed (type strain NML 06-3099T = CCUG 55408T = DSM 19846T).

Genetic and genomic diversity studies of Acacia symbionts in Senegal reveal new species of Mesorhizobium with a putative geographical pattern

Acacia senegal (L) Willd. and Acacia seyal Del. are highly nitrogen-fixing and moderately salt tolerant species. In this study we focused on the genetic and genomic diversity of Acacia mesorhizobia symbionts from diverse origins in Senegal and investigated possible correlations between the genetic diversity of the strains, their soil of origin, and their tolerance to salinity. We first performed a multi-locus sequence analysis on five markers gene fragments on a collection of 47 mesorhizobia strains of A. senegal and A. seyal from 8 localities. Most of the strains (60%) clustered with the M. plurifarium type strain ORS 1032T, while the others form four new clades (MSP1 to MSP4). We sequenced and assembled seven draft genomes: four in the M. plurifarium clade (ORS3356, ORS3365, STM8773 and ORS1032T), one in MSP1 (STM8789), MSP2 (ORS3359) and MSP3 (ORS3324). The average nucleotide identities between these genomes together with the MLSA analysis reveal three new species of Mesorhizobium. A great variability of salt tolerance was found among the strains with a lack of correlation between the genetic diversity of mesorhizobia, their salt tolerance and the soils samples characteristics. A putative geographical pattern of A. senegal symbionts between the dryland north part and the center of Senegal was found, reflecting adaptations to specific local conditions such as the water regime. However, the presence of salt does not seem to be an important structuring factor of Mesorhizobium species.

Phylogenetic diversity of Mesorhizobium in chickpea

Crop domestication, in general, has reduced genetic diversity in cultivated gene pool of chickpea (Cicer arietinum) as compared with wild species (C. reticulatum, C. bijugum). To explore impact of domestication on symbiosis, 10 accessions of chickpeas, including 4 accessions of C. arietinum, and 3 accessions of each of C. reticulatum and C. bijugum species, were selected and DNAs were extracted from their nodules. To distinguish chickpea symbiont, preliminary sequences analysis was attempted with 9 genes (16S rRNA, atpD, dnaJ, glnA, gyrB, nifH, nifK, nodD and recA) of which 3 genes (gyrB, nifK and nodD) were selected based on sufficient sequence diversity for further phylogenetic analysis. Phylogenetic analysis and sequence diversity for 3 genes demonstrated that sequences from C. reticulatum were more diverse. Nodule occupancy by dominant symbiont also indicated that C. reticulatum (60 percent) could have more various symbionts than cultivated chickpea (80 percent). The study demonstrated that wild chickpeas (C. reticulatum) could be used for selecting more diverse symbionts in the field conditions and it implies that chickpea domestication affected symbiosis negatively in addition to reducing genetic diversity.

Rhizobium yantingense sp. nov., a mineral-weathering bacterium

A Gram-stain-negative, rod-shaped bacterial strain, H66(T), was isolated from the surfaces of weathered rock (purple siltstone) found in Yanting, Sichuan Province, PR China. Cells of strain H66(T) were motile with peritrichous flagella. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain H66(T) belongs to the genus Rhizobium. It is closely related to Rhizobium huautlense SO2(T) (98.1 %), Rhizobium alkalisoli CCBAU 01393(T) (98.0 %) and Rhizobium cellulosilyticum ALA10B2(T) (98.0 %). Analysis of the housekeeping genes, recA, glnII and atpD, showed low levels of sequence similarity (<92.0 %) between strain H66(T) and other recognized species of the genus Rhizobium. The predominant components of the cellular fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0. The G+C content of strain H66(T) was 60.3 mol%. Strain H66(T) is suggested to be a novel species of the genus Rhizobium based on the low levels of DNA-DNA relatedness (ranging from 14.3 % to 40.0 %) with type strains of species of the genus Rhizobium and on its unique phenotypic characteristics. The namehttp://dx.doi.org/10.1601/nm.1279Rhizobium yantingense sp. nov. is proposed for this novel species. The type strain is H66(T) ( = CCTCC AB 2014007(T) = LMG 28229(T)).

Rhizobium paranaense sp. nov., an effective N2-fixing symbiont of common bean (Phaseolus vulgaris L.) with broad geographical distribution in Brazil

Nitrogen (N), the nutrient most required for plant growth, is key for good yield of agriculturally important crops. Common bean (Phaseolus vulgaris L.) can benefit from bacteria collectively called rhizobia, which are capable of fixing atmospheric nitrogen (N2) in root nodules and supplying it to the plant. Common bean is amongst the most promiscuous legume hosts; several described species, in addition to putative novel ones have been reported as able to nodulate this legume, although not always effectively in terms of fixing N2. In this study, we present data indicating that Brazilian strains PRF 35T, PRF 54, CPAO 1135 and H 52, currently classified as Rhizobium tropici , represent a novel species symbiont of common bean. Morphological, physiological and biochemical properties differentiate these strains from other species of the genus Rhizobium , as do BOX-PCR profiles (less than 60 % similarity), multilocus sequence analysis with recA, gyrB and rpoA (less than 96.4 % sequence similarity), DNA–DNA hybridization (less than 50 % DNA–DNA relatedness), and average nucleotide identity of whole genomes (less than 92.8.%). The novel species is effective in nodulating and fixing N2 with P. vulgaris, Leucaena leucocephala and Leucaena esculenta. We propose the name Rhizobium paranaense sp. nov. for this novel taxon, with strain PRF 35T ( = CNPSo 120T = LMG 27577T = IPR-Pv 1249T) as the type strain.

Genetic diversity and evolution of Bradyrhizobium populations nodulating Erythrophleum fordii, an evergreen tree indigenous to the southern subtropical region of China

The nodulation of Erythrophleum fordii has been recorded recently, but its microsymbionts have never been studied. To investigate the diversity and biogeography of rhizobia associated with this leguminous evergreen tree, root nodules were collected from the southern subtropical region of China. A total of 166 bacterial isolates were obtained from the nodules and characterized. In a PCR-based restriction fragment length polymorphism (RFLP) analysis of ribosomal intergenic sequences, the isolates were classified into 22 types within the genus Bradyrhizobium. Sequence analysis of 16S rRNA, ribosomal intergenic spacer (IGS), and the housekeeping genes recA and glnII classified the isolates into four groups: the Bradyrhizobium elkanii and Bradyrhizobium pachyrhizi groups, comprising the dominant symbionts, Bradyrhizobium yuanmingense, and an unclassified group comprising the minor symbionts. The nodC and nifH phylogenetic trees defined five or six lineages among the isolates, which was largely consistent with the definition of genomic species. The phylogenetic results and evolutionary analysis demonstrated that mutation and vertical transmission of genes were the principal processes for the divergent evolution of Bradyrhizobium species associated with E. fordii, while lateral transfer and recombination of housekeeping and symbiotic genes were rare. The distribution of the dominant rhizobial populations was affected by soil pH and effective phosphorus. This is the first report to characterize E. fordii rhizobia.

Rhizobium flavum sp. nov., a triazophos-degrading bacterium isolated from soil under the long-term application of triazophos

A Gram-stain-negative, non-motile, pale yellow, rod-shaped bacterial strain, YW14T, was isolated from soil and its taxonomic position was investigated by a polyphasic study. Strain YW14T did not form nodules on three different legumes, and the nodD and nifH genes were not detected by PCR. Strain YW14T contained Q-10 as the predominant ubiquinone. The major cellular fatty acid was C18 : 1ω7c. Phylogenetic analyses based on 16S rRNA gene sequences and seven housekeeping gene sequences (recA, atpD, glnII, gyrB, rpoB, dnaK and thrC) showed that strain YW14T belonged to the genus Rhizobium . Strain YW14T showed 16S rRNA gene sequence similarity of 93.4–97.3 % to the type strains of recognized species of the genus Rhizobium . DNA–DNA relatedness between strain YW14T and the type strains of Rhizobium sullae IS123T and Rhizobium yanglingense CCBAU 71623T was 19.6–25.7 %, indicating that strain YW14T was distinct from them genetically. Strain YW14T could also be differentiated from these phylogenetically related species of the genus Rhizobium by various phenotypic properties. On the basis of phenotypic properties, phylogenetic distinctiveness and genetic data, strain YW14T is considered to represent a novel species of the genus Rhizobium , for which the name Rhizobium flavum sp. nov. is proposed. The type strain is YW14T ( = KACC 17222T = CCTCC AB2013042T).

Insights into the history of a bacterial group II intron remnant from the genomes of the nitrogen-fixing symbionts Sinorhizobium meliloti and Sinorhizobium medicae

Group II introns are self-splicing catalytic RNAs that act as mobile retroelements. In bacteria, they are thought to be tolerated to some extent because they self-splice and home preferentially to sites outside of functional genes, generally within intergenic regions or in other mobile genetic elements, by mechanisms including the divergence of DNA target specificity to prevent target site saturation. RmInt1 is a mobile group II intron that is widespread in natural populations of Sinorhizobium meliloti and was first described in the GR4 strain. Like other bacterial group II introns, RmInt1 tends to evolve toward an inactive form by fragmentation, with loss of the 3′ terminus. We identified genomic evidence of a fragmented intron closely related to RmInt1 buried in the genome of the extant S. meliloti/S. medicae species. By studying this intron, we obtained evidence for the occurrence of intron insertion before the divergence of ancient rhizobial species. This fragmented group II intron has thus existed for a long time and has provided sequence variation, on which selection can act, contributing to diverse genetic rearrangements, and to generate pan-genome divergence after strain differentiation. The data presented here suggest that fragmented group II introns within intergenic regions closed to functionally important neighboring genes may have been microevolutionary forces driving adaptive evolution of these rhizobial species.

Integrating genomics into the taxonomy and systematics of the Bacteria and Archaea

The polyphasic approach used today in the taxonomy and systematics of the Bacteria and Archaea includes the use of phenotypic, chemotaxonomic and genotypic data. The use of 16S rRNA gene sequence data has revolutionized our understanding of the microbial world and led to a rapid increase in the number of descriptions of novel taxa, especially at the species level. It has allowed in many cases for the demarcation of taxa into distinct species, but its limitations in a number of groups have resulted in the continued use of DNA-DNA hybridization. As technology has improved, next-generation sequencing (NGS) has provided a rapid and cost-effective approach to obtaining whole-genome sequences of microbial strains. Although some 12,000 bacterial or archaeal genome sequences are available for comparison, only 1725 of these are of actual type strains, limiting the use of genomic data in comparative taxonomic studies when there are nearly 11,000 type strains. Efforts to obtain complete genome sequences of all type strains are critical to the future of microbial systematics. The incorporation of genomics into the taxonomy and systematics of the Bacteria and Archaea coupled with computational advances will boost the credibility of taxonomy in the genomic era. This special issue of International Journal of Systematic and Evolutionary Microbiology contains both original research and review articles covering the use of genomic sequence data in microbial taxonomy and systematics. It includes contributions on specific taxa as well as outlines of approaches for incorporating genomics into new strain isolation to new taxon description workflows.

Phylogeny of the Rhizobium-Allorhizobium-Agrobacterium clade supports the delineation of Neorhizobium gen. nov

The genera Agrobacterium, Allorhizobium, and Rhizobium belong to the family Rhizobiaceae. However, the placement of a phytopathogenic group of bacteria, the genus Agrobacterium, among the nitrogen-fixing bacteria and the unclear position of Rhizobium galegae have caused controversy in previous taxonomic studies. To resolve uncertainties in the taxonomy and nomenclature within this family, the phylogenetic relationships of generic members of Rhizobiaceae were studied, but with particular emphasis on the taxa included in Agrobacterium and the "R. galegae complex" (R. galegae and related taxa), using multilocus sequence analysis (MLSA) of six protein-coding housekeeping genes among 114 rhizobial and agrobacterial taxa. The results showed that R. galegae, R. vignae, R. huautlense, and R. alkalisoli formed a separate clade that clearly represented a new genus, for which the name Neorhizobium is proposed. Agrobacterium was shown to represent a separate cluster of mainly pathogenic taxa of the family Rhizobiaceae. A. vitis grouped with Allorhizobium, distinct from Agrobacterium, and should be reclassified as Allorhizobium vitis, whereas Rhizobium rhizogenes was considered to be the proper name for former Agrobacterium rhizogenes. This phylogenetic study further indicated that the taxonomic status of several taxa could be resolved by the creation of more novel genera.

Rhizobium rhizoryzae sp. nov., isolated from rice roots

Two strains (J3-AN59(T) and J3-N84) of Gram-stain-negative, aerobic and rod-shaped bacteria were isolated from the roots of fresh rice plants. The 16S rRNA gene sequence similarity results showed that the similarity between strains J3-AN59(T) and J3-N84 was 100 %. Both strains were phylogenetically related to members of the genus Rhizobium, and they were most closely related to Rhizobium tarimense ACCC 06128(T) (97.43 %). Similarities in the sequences of housekeeping genes between strains J3-AN59(T) and J3-N84 and those of recognized species of the genus Rhizobium were less than 90 %. The polar lipid profiles of both strains were predominantly composed of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine and an unknown aminophospholipid. The major cellular fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0. The DNA G+C contents of J3-AN59(T) and J3-N84 were 55.7 and 57.1 mol%, respectively. The DNA-DNA relatedness value between J3-AN59(T) and J3-N84 was 89 %, and strain J3-AN59(T) showed 9 % DNA-DNA relatedness to R. tarimense ACCC 06128(T), the most closely related strain. Based on this evidence, we found that J3-AN59(T) and J3-N84 represent a novel species in the genus Rhizobium and we propose the name Rhizobium rhizoryzae sp. nov. The type strain is J3-AN59(T) ( = ACCC 05916(T) = KCTC 23652(T)).

Permanent draft genome sequences of the symbiotic nitrogen fixing Ensifer meliloti strains BO21CC and AK58

Ensifer (syn. Sinorhizobium) meliloti is an important symbiotic bacterial species that fixes nitrogen. Strains BO21CC and AK58 were previously investigated for their substrate utilization and their plant-growth promoting abilities showing interesting features. Here, we describe the complete genome sequence and annotation of these strains. BO21CC and AK58 genomes are 6,985,065 and 6,974,333 bp long with 6,746 and 6,992 genes predicted, respectively.

Life in an arsenic-containing gold mine: genome and physiology of the autotrophic arsenite-oxidizing bacterium rhizobium sp. NT-26

Arsenic is widespread in the environment and its presence is a result of natural or anthropogenic activities. Microbes have developed different mechanisms to deal with toxic compounds such as arsenic and this is to resist or metabolize the compound. Here, we present the first reference set of genomic, transcriptomic and proteomic data of an Alphaproteobacterium isolated from an arsenic-containing goldmine: Rhizobium sp. NT-26. Although phylogenetically related to the plant-associated bacteria, this organism has lost the major colonizing capabilities needed for symbiosis with legumes. In contrast, the genome of Rhizobium sp. NT-26 comprises a megaplasmid containing the various genes, which enable it to metabolize arsenite. Remarkably, although the genes required for arsenite oxidation and flagellar motility/biofilm formation are carried by the megaplasmid and the chromosome, respectively, a coordinate regulation of these two mechanisms was observed. Taken together, these processes illustrate the impact environmental pressure can have on the evolution of bacterial genomes, improving the fitness of bacterial strains by the acquisition of novel functions.

Rhizobium freirei sp. nov., a symbiont of Phaseolus vulgaris that is very effective at fixing nitrogen

Common bean (Phaseolus vulgaris L.) can establish symbiotic associations with several Rhizobium species; however, the effectiveness of most strains at fixing nitrogen under field conditions is very low. PRF 81T is a very effective strain, usually referred to as Rhizobium tropici and used successfully in thousands of doses of commercial inoculants for the common bean crop in Brazil; it has shown high rates of nitrogen fixation in all areas representative of the crop in the country. Here, we present results that indicate that PRF 81T, although it belongs to the ‘ R. tropici group’, which includes 10 Rhizobium species, R. tropici , R. leucaenae , R. lusitanum , R. multihospitium , R. miluonense , R. hainanense , R. calliandrae , R. mayense , R. jaguaris and R. rhizogenes , represents a novel species. Several morpho-physiological traits differentiated PRF 81T from related species. Differences were also confirmed in the analysis of rep-PCR (sharing less than 45 % similarity with the other species), MLSA with recA, atpD and rpoB genes, and DNA–DNA hybridization. The novel species, for which we propose the name Rhizobium freirei sp. nov., is able to establish effective root nodule symbioses with Phaseolus vulgaris, Leucaena leucocephala, Leucaena esculenta, Crotalaria juncea and Macroptilium atropurpureum. The type strain is PRF 81T ( = CNPSo 122T = SEMIA 4080T = IPR-Pv81T = WDCM 440T).

Ciceribacter lividus gen. nov., sp. nov., isolated from rhizosphere soil of chick pea (Cicer arietinum L.)

The taxonomic position of strain MSSRFBL1(T), isolated from chickpea rhizosphere soil from Kannivadi, India, was determined. Strain MSSRFBL1(T) formed bluish black colonies, stained Gram-negative and was motile, aerobic, capable of fixing dinitrogen, oxidase-negative and catalase-positive. Q-10 was the major respiratory quinone. Major fatty acids of strain MSSRFBL1(T) were C18 : 1ω7c and C19 : 0cycloω8c. Minor amounts of C18 : 0, C12 : 0, C14 : 0 3-OH, C18 : 0 3-OH, C16 : 0, C16 : 1ω6c/C16 : 1ω7c, C17 : 0 3-OH and C20 : 1ω7c were also present. Polar lipids included diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylcholine and two unidentified glycolipids. Bacteriohopane derivatives (BHD1 and 2), diplopterol, diploptene, bishomohopanediol, adenosylhopane and 2β-methyl bacteriohopanetetrol were the major hopanoids of strain MSSRFBL1(T). The genomic DNA G+C content was 71 mol%. EzTaxon-e-based blast analysis of the 16S rRNA gene indicated the highest similarity of strain MSSRFBL1(T) to Ensifer adhaerens LMG 20216(T) (97.3 %) and other members of the genus Ensifer (<96.9 %) in the family Rhizobiaceae of the class Alphaproteobacteria. However, phylogenetic analysis based on 16S rRNA, recA, thrC and dnaK gene sequences showed distinct out-grouping from the recognized genera of the family Rhizobiaceae. Based on phenotypic, genotypic and chemotaxonomic characters, strain MSSRFBL1(T) represents a novel species in a new genus in the family Rhizobiaceae for which the name Ciceribacter lividus gen. nov., sp. nov. is proposed. The type strain of Ciceribacter lividus is MSSRFBL1(T) ( = DSM 25528(T) = KCTC 32403(T)).

Polyphasic characterization of rhizobia isolated from Leucaena leucocephala from Panxi, China

Leucaena leucocephala was introduced into Panxi, Sichuan, China, in the 1980s and 1990s for afforestation and preventing water loss and soil erosion in this area. The co-introduction of rhizobial symbionts of introduced plants has drawn attention since they may influence local soil communities. We studied the phylogenetic position of the L. leucocephala isolates and assessed if the rhizobia were introduced together with the host to Panxi, Sichuan, China. The glnII and atpD genes of fifteen representative isolates were sequenced and analyzed, and applied multilocus sequence analyses in which the housekeeping genes recA, glnII and atpD were included. Furthermore, we estimated the within species diversity directly with 23S rDNA and IGS RFLP and indirectly through phenotypic analysis of forty L. leucocephala isolates. The isolates represented seven species and 38 diversified strains in the genera Ensifer, Mesorhizobium, Bradyrhizobium and Rhizobium. The within species diversity of the Ensifer isolates was large, proposing a potential to occupy novel niches. There was not conclusive evidence to show that any of the strains would have been co-introduced with L. leucocephala. On the contrary, we came to a conclusion that the possible introduction should not be inferred from sequence data alone.