Analysis of cellular fatty acids and phenotypic relationships of Agrobacterium, Bradyrhizobium, Mesorhizobium, Rhizobium and Sinorhizobium species using the Sherlock Microbial Identification System

Bradyrhizobium ontarionense sp. nov., a novel bacterial symbiont isolated from Aeschynomene indica (Indian jointvetch), harbours photosynthesis, nitrogen fixation and nitrous oxide (N2O) reductase genes

A novel bacterial symbiont, strain A19T, was previously isolated from a root-nodule of Aeschynomene indica and assigned to a new lineage in the photosynthetic clade of the genus Bradyrhizobium. Here data are presented for the detailed genomic and taxonomic analyses of novel strain A19T. Emphasis is placed on the analysis of genes of practical or ecological significance (photosynthesis, nitrous oxide reductase and nitrogen fixation genes). Phylogenomic analysis of whole genome sequences as well as 50 single-copy core gene sequences placed A19T in a highly supported lineage distinct from described Bradyrhizobium species with B. oligotrophicum as the closest relative. The digital DNA-DNA hybridization and average nucleotide identity values for A19T in pair-wise comparisons with close relatives were far lower than the respective threshold values of 70% and ~ 96% for definition of species boundaries. The complete genome of A19T consists of a single 8.44 Mbp chromosome and contains a photosynthesis gene cluster, nitrogen-fixation genes and genes encoding a complete denitrifying enzyme system including nitrous oxide reductase implicated in the reduction of N2O, a potent greenhouse gas, to inert dinitrogen. Nodulation and type III secretion system genes, needed for nodulation by most rhizobia, were not detected. Data for multiple phenotypic tests complemented the sequence-based analyses. Strain A19T elicits nitrogen-fixing nodules on stems and roots of A. indica plants but not on soybeans or Macroptilium atropurpureum. Based on the data presented, a new species named Bradyrhizobium ontarionense sp. nov. is proposed with strain A19T (= LMG 32638T = HAMBI 3761T) as the type strain.

Characterization and Genomic Analysis of Fererhizobium litorale gen. nov., sp. nov., Isolated from the Sandy Sediments of the Sea of Japan Seashore

The taxonomic status of two gram-negative, whitish-pigmented motile bacteria KMM 9576T and KMM 9553 isolated from a sandy sediment sample from the Sea of Japan seashore was defined. Phylogenetic analysis revealed that strains KMM 9576T and KMM 9553 represent a distinct lineage within the family Rhizobiaceae, sharing 100% 16S rRNA sequence similarity and 99.5% average nucleotide identity (ANI) to each other. The strains showed the highest 16S rRNA sequence similarities of 97.4% to Sinorhizobium garamanticum LMG 24692T, 96.9% to Ensifer adhaerens NBRC 100388T, and 96.8% to Pararhizobium giardinii NBRC 107135T. The ANI values between strain KMM 9576T and Ensifer adhaerens NBRC 100388T, Sinorhizobium fredii USDA 205T, Pararhizobium giardinii NBRC 107135T, and Rhizobium leguminosarum NBRC 14778T were 79.9%, 79.6%, 79.4%, and 79.2%, respectively. The highest core-proteome average amino acid identity (cpAAI) values of 82.1% and 83.1% were estimated between strain KMM 9576T and Rhizobium leguminosarum NBRC 14778T and 'Rhizobium album' NS-104, respectively. The DNA GC contents were calculated from a genome sequence to be 61.5% (KMM 9576T) and 61.4% (KMM 9553). Both strains contained the major ubiquinone Q-10 and C18:1ω7c as the dominant fatty acid followed by 11-methyl C18:1ω7c and C19:0 cyclo, and polar lipids consisted of phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, an unidentified aminophospholipid, and two unidentified phospholipids. Based on phylogenetic and phylogenomic analyses, and phenotypic characterization, strains KMM 9576T and KMM 9553 are concluded to represent a novel genus and species, for which the name Fererhizobium litorale gen. nov., sp. nov. is proposed. The type strain of the type species is strain KMM 9576T (=NRIC 0957T).

Phylogenomic reappraisal of the family Rhizobiaceae at the genus and species levels, including the description of Ectorhizobium quercum gen. nov., sp. nov

The family Rhizobiaceae contains 19 validly described genera including the rhizobia groups, many of which are important nitrogen-fixing bacteria. Early classification of Rhizobiaceae relied heavily on the poorly resolved 16S rRNA genes and resulted in several taxonomic conflicts. Although several recent studies illustrated the taxonomic status of many members in the family Rhizobiaceae, several para- and polyphyletic genera still needed to be elucidated. The rapidly increasing number of genomes in Rhizobiaceae has allowed for a revision of the taxonomic identities of members in Rhizobiaceae. In this study, we performed analyses of genome-based phylogeny and phylogenomic metrics to review the relationships of 155-type strains within the family Rhizobiaceae. The UBCG and concatenated protein phylogenetic trees, constructed based on 92 core genes and concatenated alignment of 170 single-copy orthologous proteins, demonstrated that the taxonomic inconsistencies should be assigned to eight novel genera, and 22 species should be recombined. All these reclassifications were also confirmed by pairwise cpAAI values, which separated genera within the family Rhizobiaceae with a demarcation threshold of ~86%. In addition, along with the phenotypic and chemotaxonomic analyses, a novel strain BDR2-2T belonging to a novel genus of the family Rhizobiaceae was also confirmed, for which the name Ectorhizobium quercum gen. nov., sp. nov. was proposed. The type strain is BDR2-2T (=CFCC 16492T = LMG 31717T).

Ensifer canadensis sp. nov. strain T173T isolated from Melilotus albus (sweet clover) in Canada possesses recombinant plasmid pT173b harbouring symbiosis and type IV secretion system genes apparently acquired from Ensifer medicae

A bacterial strain, designated T173^T, was previously isolated from a root-nodule of a Melilotus albus plant growing in Canada and identified as a novel Ensifer lineage that shared a clade with the non-symbiotic species, Ensifer adhaerens. Strain T173^T was also previously found to harbour a symbiosis plasmid and to elicit root-nodules on Medicago and Melilotus species but not fix nitrogen. Here we present data for the genomic and taxonomic description of strain T173^T. Phylogenetic analyses including the analysis of whole genome sequences and multiple locus sequence analysis (MLSA) of 53 concatenated ribosome protein subunit (rps) gene sequences confirmed placement of strain T173^T in a highly supported lineage distinct from named Ensifer species with E. morelensis Lc04^T as the closest relative. The highest digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values of genome sequences of strain T173^T compared with closest relatives (35.7 and 87.9%, respectively) are well below the respective threshold values of 70% and 95-96% for bacterial species circumscription. The genome of strain T173^T has a size of 8,094,229 bp with a DNA G + C content of 61.0 mol%. Six replicons were detected: a chromosome (4,051,102 bp) and five plasmids harbouring plasmid replication and segregation (repABC) genes. These plasmids were also found to possess five apparent conjugation systems based on analysis of TraA (relaxase), TrbE/VirB4 (part of the Type IV secretion system (T4SS)) and TraG/VirD4 (coupling protein). Ribosomal RNA operons encoding 16S, 23S, and 5S rRNAs that are usually restricted to bacterial chromosomes were detected on plasmids pT173d and pT173e (946,878 and 1,913,930 bp, respectively) as well as on the chromosome of strain T173^T. Moreover, plasmid pT173b (204,278 bp) was found to harbour T4SS and symbiosis genes, including nodulation (nod, noe, nol) and nitrogen fixation (nif, fix) genes that were apparently acquired from E. medicae by horizontal transfer. Data for morphological, physiological and symbiotic characteristics complement the sequence-based characterization of strain T173^T. The data presented support the description of a new species for which the name Ensifer canadensis sp. nov. is proposed with strain T173^T (= LMG 32374^T = HAMBI 3766^T) as the species type strain.

Strains of Bradyrhizobium barranii sp. nov. associated with legumes native to Canada are symbionts of soybeans and belong to different subspecies (subsp. barranii subsp. nov. and subsp. apii subsp. nov.) and symbiovars (sv. glycinearum and sv. septentrionale)

Four bacterial strains isolated from root nodules of soybean plants that had been inoculated with root-zone soils of legumes native to Canada were previously identified as a novel Bradyrhizobium lineage consisting of symbiovars (sv.) glycinearum and septentrionale. Our purpose was to verify the taxonomic status of these strains using phylogenetic, genomic and phenotypic analyses. Multiple phylogenetic analyses including analysis of 51 full-length ribosome protein subunit (rps) gene sequences confirmed placement of the novel strains in a highly supported lineage distinct from named Bradyrhizobium species with B. japonicum USDA 6T as the closest relative. The results of genomic and phylogenomic analyses based on digital DNA–DNA hybridization and genome blast distance phylogeny showed that novel strains in comparisons with type strains of closest relatives were below the established threshold (70 %) for species delineation. Moreover, the novel strains were divided into two subspecies clusters based on the established threshold of 79 %. The genomes of strains 144S4T, 323S2, 1S5 and 38S5T have sizes of 11 399 526, 11 474 152, 10580853 and 10 530 141 bp with DNA G+C contents of 63.1, 63.0, 63.4 and 63.3 mol%, respectively. These strains possess symbiosis islands harbouring key nodulation, nitrogen-fixation and type III secretion system genes as well as abundant insertion sequences and between two and four putative plasmids. Strains 144S4T and 323S2 (sv. glycinearum) are effective with regard to nitrogen fixation in symbiotic association with soybeans whereas strains 1S5 and 38S5T (sv. septentrionale) are ineffective. Data for morphological, physiological and symbiotic characteristics complement the sequence-based results. The data presented here support the description of a new species and two new subspecies for which the names Bradyrhizobium barranii sp. nov. subsp. barranii subsp. nov. (sv. glycinearum) and Bradyrhizobium barranii sp. nov. subsp. apii subsp. nov. (sv. septentrionale) are proposed with strain 144S4T (=LMG 31552T=HAMBI 3722T) as the species type strain and type strain of subsp. barranii subsp. nov., and strain 38S5T (=LMG 31556T=HAMBI 3721T) as the type strain of subsp. apii subsp. nov.

Rhizobium quercicola sp. nov., isolated from the leaf of Quercus variablis in China

Strain DKSPLA3^T, a novel Gram-negative, catalase-positive, oxidase-positive, non-spore-forming, aerobic, non-nitrogen-fixing, non-motile bacterium was isolated from Quercus variablis leaf, in Zunyi, Guizhou, China. Growth occurred at 4-37 °C (optimum 28 °C), pH 4.0-9.0 (optimum pH 7.0) and up to 4.0% (w/v) NaCl (optimum under 2.0%, w/v). Phylogeny based on 16S rRNA gene indicated that strain DKSPLA3^T was a novel species in the genus Rhizobium, which was supported by average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values. The predominant fatty acids of strain DKSPLA3^T were C_16:0, C_18:1 ω7c and/or C_18:1 ω6c and C_18:1 ω7c 11-methyl. The major respiratory quinone was Q-10. Major polar lipids were diphosphatidyl glycerol (DPG), phosphatidyl glycerol (PG), phosphatidylethanolamine (PE), phosphatidylmonomethylethanolamine (PME), phosphatidylcholine (PC), two unidentified phospholipids (PL) and nine unidentified lipids (L). The genomic G + C content was 64.47 mol%. Based on the phenotypic, phylogenetic and genotypic data, DKSPLA3^T should be classified as a novel species in the genus Rhizobium, for which the name Rhizobium quercicola sp. nov. (KCTC 82843^T = CFCC 16,707T) is proposed.

The changing paradigm of rhizobial taxonomy and its systematic growth upto postgenomic technologies

Rhizobia are a diazotrophic group of bacteria that are usually isolated form the nodules in roots, stem of leguminous plants and are able to form nodules in the host plant owing to the presence of symbiotic genes. The rhizobial community is highly diverse, and therefore, the taxonomy and genera-wise classification of rhizobia has been constantly changing since the last three decades. This is mainly due to technical advancements, and shifts in definitions, resulting in a changing paradigm of rhizobia taxonomy. Initially, the taxonomic definitions at the species and sub species level were based on phylogenetic analysis of 16S rRNA sequence, followed by polyphasic approach to have phenotypic, biochemical, and genetic analysis including multilocus sequence analysis. Rhizobia mainly belonging to α- and β-proteobacteria, and recently new additions from γ-proteobacteria had been classified. Nowadays rhizobial taxonomy has been replaced by genome-based taxonomy that allows gaining more insights of genomic characteristics. These omics-technologies provide genome specific information that considers nodulation and symbiotic genes, along with molecular markers as taxonomic traits. Taxonomy based on complete genome sequence (genotaxonomy), average nucleotide identity, is now being considered as primary approach, resulting in an ongoing paradigm shift in rhizobial taxonomy. Also, pairwise whole-genome comparisons, phylogenomic analyses offer correlations between DNA and DNA re-association values that have delineated biologically important species. This review elaborates the present classification and taxonomy of rhizobia, vis-a-vis development of technical advancements, parameters and controversies associated with it, and describe the updated information on evolutionary lineages of rhizobia.

Isolation, genomic characterization, and mushroom growth-promoting effect of the first fungus-derived Rhizobium

Polyporus umbellatus is a well-known edible and medicinal mushroom, and some bacteria isolated from mushroom sclerotia may have beneficial effects on their host. These mushroom growth-promoting bacteria (MGPBs) are of great significance in the mushroom production. In this work, we aimed to isolate and identify MGPBs from P. umbellatus sclerotia. Using the agar plate dilution method, strain CACMS001 was isolated from P. umbellatus sclerotia. The genome of CACMS001 was sequenced using PacBio platform, and the phylogenomic analysis indicated that CACMS001 could not be assigned to known Rhizobium species. In co-culture experiments, CACMS001 increased the mycelial growth of P. umbellatus and Armillaria gallica and increased xylanase activity in A. gallica. Comparative genomic analysis showed that CACMS001 lost almost all nitrogen fixation genes but specially acquired one redox cofactor cluster with pqqE, pqqD, pqqC, and pqqB involved in the synthesis of pyrroloquinoline quinone, a peptide-derived redox participating in phosphate solubilization activity. Strain CACMS001 has the capacity to solubilize phosphate using Pikovskaya medium, and phnA and phoU involved in this process in CACMS001 were revealed by quantitative real-time PCR. CACMS001 is a new potential Rhizobium species and is the first identified MGPB belonging to Rhizobium. This novel bacterium would play a vital part in P. umbellatus, A. gallica, and other mushroom cultivation.

Rhizobium setariae sp. nov., an Indole-3-Acetic Acid-Producing Bacterium Isolated from Green Foxtail, Setaria viridis

A Gram-negative, indole-3-acetic acid-producing, aerobic, motile strain, designated as KVB221^T, was isolated from a green foxtail plant, Setaria viridis, from a park near the coast of Haeundae Beach, Busan, Republic of Korea. The 16S rRNA gene analysis revealed strain KVB221^T to be a member of the genus Rhizobium, from which Rhizobium alvei TNR-22^T (97.2%), Rhizobium daejeonense L61^T (96.9%), and Rhizobium ipomoeae shin9-1^T (95.7%) were selected for comparative analysis. Growth of the strain was observed at 10-50 °C (optimum 25-30 °C), at pH 5-10 (optimum pH 7), and in the presence of 0-8% NaCl (optimum 0%). The strain was observed to produce 36.3 ± 0.8 μg/ml of indole following 5 days of incubation. The major fatty acids are comprised of C_16:0, C_19:0 cyclo ω8c, C_18:1 ω7c, and the unresolved group summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c), while major polar lipids are identified as phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylmonomethylethanolamine (PME). The predominant quinone is Q-10 and the DNA G+C content of the strain is 59.3%. Based on publicly available genome data between strain KVB221^T and its closely related strains, the average nucleotide identity and in silico DNA-DNA hybridization values ranged from 72.7 to 73.1 and 19.7 to 20.4%, respectively. Based on the chemotaxonomic, phenotypic, and genomic comparisons reported here, we propose Rhizobium setariae sp. nov. as a novel species belonging to the genus Rhizobium. The type strain is KVB221^T (= KACC 21713^T = NBRC 114644^T).

Genetic and Chemical Diversity of Edible Mushroom Pleurotus Species

The genus Pleurotus is one of the most widely cultivated and edible mushrooms with various cultivators. Three molecular characteristics were used to evaluate the genetic diversity of 132 tested samples. Phylogenetic analysis showed five clades for tested samples of the genus Pleurotus by the combined ITS and LSU sequences with strong bootstraps and Bayesian posterior probability supports. A total of 94 polymorphic fragments ranging from 10 to 100 bp were observed by using an intersimple sequence repeat (ISSR) marker. The DNA fragment pattern showed that P. ostreatus cultivator (strain P9) was clearly distinguished from wild strain based on their clear banding profiles produced. DNA GC content of the genus Pleurotus varied from 55.6 mol% to 43.3 mol%. Their chemical composition was also determined, including sugar, amino acid, polar lipid, mycolic acid, quinone, and fatty acid, which presented some high homogeneity. Most of the tested samples contained mycolic acid; glucose and arabinose as the main sugars; aspartic acid, arginine, lysine, tyrosine, and alanine as the main amino acids; and C_16:0, C_18:0, C_18:2cis-9,12, anteiso-C_14:0, and summed feature 8 as the main fatty acids. In addition, their polar lipid profiles were investigated for the first time, which significantly varied among Pleurotus species. The genus Pleurotus contained menaquinone-6 as the sole respiratory quinone, which showed a significant difference with that of its closely related genera. These results of this study demonstrated that the combined method above could efficiently differentiate each Pleurotus species and thus be considered an efficient tool for surveying the genetic diversity of the genus Pleurotus.

Membrane Homeoviscous Adaptation in Sinorhizobium Submitted to a Stressful Thermal Cycle Contributes to the Maintenance of the Symbiotic Plant–Bacteria Interaction

Here, we estimate fast changes in the fluidity of Sinorhizobium meliloti membranes submitted to cyclic temperature changes (10°C–40°C–10°C) by monitoring the fluorescence polarization (P) of DPH and TMA-DPH of the whole cell (WC) as well as in its outer (OM) and inner (IM) membranes. Additionally, the long-term response to thermal changes is demonstrated through the dynamics of the phospholipid and fatty acid composition in each membrane. This allowed membrane homeoviscous adaptation by the return to optimal fluidity levels as measured by the PDPH/TMA-DPH in WC, OM, IM, and multilamellar vesicles of lipids extracted from OM and IM. Due to probe-partitioning preferences and membranes’ compositional characteristics, DPH and TMA-DPH exhibit different behaviors in IM and OM. The rapid effect of cyclic temperature changes on the P was the opposite in both membranes with the IM being the one that exhibited the thermal behavior expected for lipid bilayers. Interestingly, only after the incubation at 40°C, cells were unable to recover the membrane preheating P levels when cooled up to 10°C. Solely in this condition, the formation of threads and nodular structures in Medicago sativa infected with S. meliloti were delayed, indicating that the symbiotic interaction was partially altered but not halted.

Mesorhizobium comanense sp. nov., isolated from groundwater

Strain 3P27G6^T was isolated from an artesian well connected to the thermal water basin of Comano Terme, Province of Trento, Italy. In phylogenetic analyses based on multilocus sequence analysis, strain 3P27G6^T clustered together with Mesorhizobium australicum WSM2073^T. Genome sequencing produced a 99.51 % complete genome, with a length of 7 363 057 bp and G+C content of 63.53 mol%, containing 6897 coding sequences, 55 tRNA and three rRNA. Average nucleotide identity analysis revealed that all distances calculated between strain 3P27G6^T and the other Mesorhizobium genomes were below 0.9, indicating that strain 3P27G6^T represents a new species. Therefore, we propose the name Mesorhizobium comanense sp. nov. with the type strain 3P27G6^T (=DSM 110654^T=CECT 30067^T). Strain 3P27G6^T is a Gram-negative, rod-shaped, aerobic bacterium. Growth condition, antibiotic susceptibility, metabolic and fatty acid-methyl esters profiles of the strain were determined. Only few nodulation and nitrogen fixation genes were found in the genome, suggesting that this strain may not be specialized in nodulation or in nitrogen fixation.

The Comparisons of Fatty Acid Composition in Some Anaerobic Gut Fungi Neocallimastix, Orpinomyces, Piromyces, and Caecomyces

The objective of this study were to identify the fatty acid composition for decanoic (C10:0), tridecanoic (C13:0), myristic (C14:0), pentadecanoic (C15:0), palmitic (C16:0), stearic (C18:0), oleic (C18:1n9c), linoleic (C18:2n6c), arachidic (C20:0), arachidonic (C20:4n6), heneicosanoic (C21:0), erucic (C22:1n9) and Cis-4,7,10,13,16,19-docosahexaenoic (C22:6n3) acids by Neocallimastix, Orpinomyces, Caecomyces and Piromyces species of rumen fungus during in vitro culture. Fatty acid (FA) profi le of anaerobic fungi comprises carbon chains of length ranging from 10 to 22 were analyzed as methyl esters. Analysis of fatty acids was performed using Gas Chromatography-Mass Spectrophotometer (GC-MS). FA measures are presented as proportions of relative amounts (% total fatty acid). The highest amounts of fatty acids for all samples were found as myristic (C14:0) acid. The tridecanoic (C13:0) acid represented the second abundant FA in the fungi in all experimental groups. Stearic acid (C18:0) was the third major fatty acid for isolates investigated in the current study. In addition, another fatty acid was palmitic (C16:0) acid with relative amount representing >20 % of total FA in all samples. Pentadecanoic (C15:0) acid could not be found in any other samples except Orpinomyces sp. (GMLF5). It is concluded that biohydrogenation of fatty acid composition by anaerobic gut fungi are very variable.

Long-term cover crops improved soil phosphorus availability in a rain-fed apple orchard

The objective of this present study was to understand the distribution patterns of various forms of soil phosphorus (P) and the biotic and abiotic factors affecting the soil P fractions under long-term cover crops. Here, we investigated the characteristics of soil P forms, community structure of P-solubilizing bacteria (using 16S rRNA) and the related enzyme activity under clean tillage (CT), 14 years of white clover (WC, Trifolium repens L.) and orchard grass (OG, Dactylis glomerata L.) cover crops in a rain-fed apple orchard on the Weibei Loess Plateau, China. Relative to CT treatment, long-term cover crops enhanced the bioavailability of soil P by increasing the contents of total phosphorus (TP), microbial phosphorus (MBP), organic phosphorus (Po) and certain forms of inorganic phosphorus (e.g. Al-P, Ca₂-P, Ca₈-P and Fe-P) in the surface soil, in addition, WC treatment also increase the available P (AP) contents in the topsoil. A redundant analysis (RDA) showed that soil organic matter (SOM), NH₄⁺-N and pH were the key environmental factors affecting the morphological changes of soil P. In addition, the effects of long-term cover crops on soil P forms were mainly concentrated in the topsoil, and the WC treatment had a greater impact on soil P composition than the OG treatment. Interestingly, long-term cover crops effectively increased the abundances of P-solubilizing bacteria, such as Streptomyces, Sphingomonas, Nocardioides and Haliangium, and enhanced the alkaline phosphatase (ALP) activity. Overall, long-term cover crops were an effective strategy to activate soil P as they improve the soil environment.

Bradyrhizobium septentrionale sp. nov. (sv. septentrionale) and Bradyrhizobium quebecense sp. nov. (sv. septentrionale) associated with legumes native to Canada possess rearranged symbiosis genes and numerous insertion sequences

Six bacterial strains isolated from root nodules of soybean plants that had been inoculated with root-zone soil of legumes native to Canada were previously characterized and 1) placed in two novel lineages within the genus Bradyrhizobium and 2) assigned to symbiovar septentrionale. Here we verified the taxonomic status of these strains using genomic and phenotypic analyses. Phylogenetic analyses of five protein encoding partial gene sequences as well as 52 full length ribosome protein subunit gene sequences confirmed placement of the novel strains in two highly supported lineages distinct from named Bradyrhizobium species. The highest average nucleotide identity values of strains representing these two lineages relative to type strains of closest relatives were 90.7 and 92.3% which is well below the threshold value for bacterial species circumscription. The genomes of representative strains 1S1^T, 162S2 and 66S1MB^T have sizes of 10598256, 10733150 and 9032145 bp with DNA G+C contents of 63.5, 63.4 and 63.8 mol%, respectively. These strains possess between one and three plasmids based on copy number of plasmid replication and segregation (repABC) genes. Novel strains also possess numerous insertion sequences, and, relative to reference strain Bradyrhizobium diazoefficiens USDA110^T, exhibit inversion and fragmentation of nodulation (nod) and nitrogen-fixation (nif) gene clusters. Phylogenetic analyses of nodC and nifH gene sequences confirmed placement of novel strains in a distinct lineage corresponding to symbiovar septentrionale. Data for morphological, physiological and symbiotic characteristics complement the sequence-based results. The data presented here support the description of two new species for which the names Bradyrhizobium septentrionale sp. nov. (sv. septentrionale) and Bradyrhizobium quebecense sp. nov. (sv. septentrionale) are proposed, with 1S1^T (=LMG 29930^T=HAMBI 3676^T) and 66S1MB^T (=LMG 31547^T=HAMBI 3720^T) as type strains, respectively.

Rhizobium rhizolycopersici sp. nov., Isolated from the Rhizosphere Soil of Tomato Plants in China

During characterization of rhizobacteria, strain DBTS2^T was isolated from the rhizosphere soil samples of healthy tomato plants and characterized using a polyphasic taxonomic approach. Phylogenetic analysis using 16S rRNA gene sequences showed this strain belonged to the genus Rhizobium and was most closely related to Rhizobium subbaraonis JC85^T (99.1%) and Rhizobium daejeonense CCBAU 10050^T (97%). Cells of strain DBTS2^T were Gram-negative, short rod, aerobic and non-motile. This novel strain was found to grow at 20-45 °C (optimum 25-37 °C), pH 5-9 (optimum 8) and in the presence of 4% NaCl. It was positive for catalase and oxidase. The predominant cellular fatty acids were Summed Feature 8 (52.7%) and C_19:0 cyclo ω8c (23.3%). The polar lipids of strain DBTS2^T consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, unidentified aminophospholipid, unidentified aminolipid, four unidentified phospholipids, unidentified lipid, phosphatidylcholine, unknown glycolipid and unknown aminophosphoglycolipids. Q-10 was the major quinone. The DNA-DNA hybridization similarity values between the strain DBTS2^T and R. subbaraonis JC85^T, R. daejeonense CCBAU 10050^T and Rhizobium azooxidifex DSM100211^T were 46.4%, 20.7% and 25.5%, respectively. The ANI value was 91.96% between strain DBTS2^T and R. subbaraonis JC85^T and 75.18% between strain DBTS2^T and R. daejeonense CCBAU 10050^T. The DNA G+C content of the genomic DNA was 63.1 mol%. Based on these results, it was concluded that the isolate represents a novel species of the genus Rhizobium, for which the name Rhizobium rhizolycopersici sp. nov. is proposed, with DBTS2^T (= CICC 24887^T = ACCC61707 = JCM 34245) as the type strain.

Rhizobium rhizophilum sp. nov., an indole acetic acid-producing bacterium isolated from rape (Brassica napus L.) rhizosphere soil

A novel Gram-stain-negative, aerobic, rod-shaped and indole acetic acid-producing strain, designated 7209-2^T, was isolated from rhizosphere of rape (Brassica napus L.) grown in the Yakeshi City, Inner Mongolia, PR China. The 16S rRNA gene sequence analysis indicated that strain 7209-2^T belongs to the genus Rhizobium and is closely related to Rhizobium rosettiformans W3^T, Rhizobium ipomoeae shin9-1^T and Rhizobium wuzhouense W44^T with sequence similarities of 98.2, 98.1 and 97.9 %, respectively. Phylogenetic analysis based on concatenated housekeeping recA and atpD gene sequences showed that strain 7209-2^T formed a group together with R. wuzhouense W44^T and R. rosettiformans W3^T, with sequences similarities of 92.6 and 91.1 %, respectively. The genome size of strain 7209-2^T was 5.25 Mb, comprising 5027 predicted genes with a DNA G+C content of 61.2 mol%. The average nucleotide identity and digital DNA-DNA hybridization comparisons among 7209-2^T and reference strains for the most closely related species showed values below the accepted threshold for species discrimination. The major fatty acids of strain 7209-2^T were summed feature 8 (C_18 : 1  ω7c and/or C_18 : 1  ω6c) and summed feature 2 (C_12 : 0 aldehyde and/or unknown 10.953) . The major polar lipids were found to consist of phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine and an unidentified aminophospholipid. The predominant ubiquinone was identified as quinone 10. Based on all the above results, strain 7209-2^T represents a novel species of the genus Rhizobium, for which the name Rhizobium rhizophilum sp. nov. is proposed with 7209-2^T (=CGMCC 1.15691^T=DSM 103161^T) as the type strain.

Strains of Bradyrhizobium cosmicum sp. nov., isolated from contrasting habitats in Japan and Canada possess photosynthesis gene clusters with the hallmark of genomic islands

The taxonomic status of two previously characterized Bradyrhizobium strains (58S1T and S23321) isolated from contrasting habitats in Canada and Japan was verified by genomic and phenotypic analyses. Phylogenetic analyses of five and 27 concatenated protein-encoding core gene sequences placed both strains in a highly supported lineage distinct from named species in the genus Bradyrhizobium with Bradyrhizobium betae as the closest relative. Average nucleotide identity values of genome sequences between the test and reference strains were between 84.5 and 94.2 %, which is below the threshold value for bacterial species circumscription. The complete genomes of strains 58S1T and S23321 consist of single chromosomes of 7.30 and 7.23 Mbp, respectively, and do not have symbiosis islands. The genomes of both strains have a G+C content of 64.3 mol%. Present in the genome of these strains is a photosynthesis gene cluster (PGC) containing key photosynthesis genes. A tRNA gene and its partial tandem duplication were found at the boundaries of the PGC region in both strains, which is likely the hallmark of genomic island insertion. Key nitrogen-fixation genes were detected in the genomes of both strains, but nodulation and type III secretion system genes were not found. Sequence analysis of the nitrogen fixation gene, nifH, placed 58S1T and S23321 in a novel lineage distinct from described Bradyrhizobium species. Data for phenotypic tests, including growth characteristics and carbon source utilization, supported the sequence-based analyses. Based on the data presented here, a novel species with the name Bradyrhizobium cosmicum sp. nov. is proposed with 58S1T (=LMG 31545T=HAMBI 3725T) as the type strain.

Rhizobium dioscoreae sp. nov., a plant growth-promoting bacterium isolated from yam (Dioscorea species)

This study investigated endophytic nitrogen-fixing bacteria isolated from two species of yam (water yam, Dioscorea alata L.; lesser yam, Dioscorea esculenta L.) grown in nutrient-poor alkaline soil conditions on Miyako Island, Okinawa, Japan. Two bacterial strains of the genus Rhizobium, S-93^T and S-62, were isolated. The phylogenetic tree, based on the almost-complete 16S rRNA gene sequences (1476 bp for each strain), placed them in a distinct clade, with Rhizobium miluonense CCBAU 41251^T, Rhizobium hainanense I66^T, Rhizobium multihospitium HAMBI 2975^T, Rhizobium freirei PRF 81^T and Rhizobium tropici CIAT 899^T being their closest species. Their bacterial fatty acid profile, with major components of C_19 : 0 cyclo ω8c and summed feature 8, as well as other phenotypic characteristics and DNA G+C content (59.65 mol%) indicated that the novel strains belong to the genus Rhizobium. Pairwise average nucleotide identity analyses separated the novel strains from their most closely related species with similarity values of 90.5, 88.9, 88.5, 84.5 and 84.4 % for R. multihospitium HAMBI 2975^T, R. tropici CIAT 899^T, R. hainanense CCBAU 57015^T, R. miluonense HAMBI 2971^T and R. freirei PRF 81^T, respectively; digital DNA–DNA hybridization values were in the range of 26–42 %. Considering the phenotypic characteristics as well as the genomic data, it is suggested that strains S-93^T and S-62 represent a new species, for which the name Rhizobium dioscoreae is proposed. The type strain is S-93^T (=NRIC 0988^T=NBRC 114257^T=DSM 110498^T).

Investigating the variation of dissolved organic matters and the evolution of autotrophic microbial community in composting with organic and inorganic carbon sources

The main purpose of this study was to analyze the effects of different carbon source (Na₂CO₃, NC; sugarcane molasses, SM) additives on dissolved organic matter (DOM), cbbL-containing autotrophic microbes (CCAM), and the relationship among physico-chemical parameters, DOM and CCAM to better understand carbon transformation in composting. The results showed that SM or NC additive could promote the degradation and transformation of OM and DOM. After adding SM or NC, the Simpson index decreased by 2.03% and 0.51%, respectively, and Luteimonas and Thermomonspora were detected using high throughput sequencing, indicating that SM and NC increased the diversity of CCAM community. Additionally, both NC and SM contributed to improve the abundance of cbbL gene (45.91% and 2.15%) based on fluorescence quantitative PCR (qPCR) analysis at the cooling phase of composting. Pearson correlation analysis revealed that Proteoobacteria, Firmicutes, Acidobacteria and Nematoda were positively related with C/N, OM and DOM (0.5 < R < 0.9, P < 0.05).

Isolation, Identification and Characterization of Endophytic Bacterium Rhizobium oryzihabitans sp. nov., from Rice Root with Biotechnological Potential in Agriculture

A flagellate, rod–shaped bacterium designated strain M15^T was isolated from rice roots. Phylogenetic analysis based on the sequences of the 16S rRNA, housekeeping genes and genomes showed that the isolate belonged to the genus Rhizobium, with the highest 16S rRNA similarity to Rhizobium radiobacter LMG140^T (99.64%) and Rhizobium pusense NRCPB10^T (99.36%), respectively. The complete genome of the strain M15^T has a 59.28% G+C content, and the highest average nucleotide identity (ANI) and DNA-DNA relatedness (DDH) values were obtained with R. radiobacter LMG140^T (88.11%, 54.80%), R. pusense NRCPB10^T (86.00%, 53.00%) and R. nepotum 39/7^T (88.80%, 49.80%), respectively. Plant growth-promoting characteristics tests showed that the strain M15^T produced siderophore, 1–aminocyclopropane–1–carboxylate (ACC) deaminase and indole-3-acetic acid (IAA) and also produced some secondary metabolites according to the analysis of the comparative genomes. Based on the data mentioned above, we proposed that the strain M15^T represented a novel species of the genus Rhizobium, named Rhizobium oryzihabitans sp. nov. The type strain is M15^T (=JCM 32903^T  = ACCC 60121^T), and the strain M15^T can be a novel biofertilizer Rhizobium to reduce the use of synthetic fertilizers for plant growth promotion.

Bradyrhizobium ivorense sp. nov. as a potential local bioinoculant for Cajanus cajan cultures in Côte d'Ivoire

For many smallholder farmers of Sub-Saharan Africa, pigeonpea (Cajanus cajan) is an important crop to make ends meet. To ascertain the taxonomic status of pigeonpea isolates of Côte d’Ivoire previously identified as bradyrhizobia, a polyphasic approach was applied to strains CI-1B^T, CI-14A, CI-19D and CI-41S. Phylogeny of 16S ribosomal RNA (rRNA) genes placed these nodule isolates in a separate lineage from current species of the B. elkanii super clade. In phylogenetic analyses of single and concatenated partial dnaK, glnII, gyrB, recA and rpoB sequences, the C. cajan isolates again formed a separate lineage, with strain CI-1B^T sharing the highest sequence similarity (95.2 %) with B. tropiciagri SEMIA 6148^T. Comparative genomic analyses corroborated the novel species status, with 86 % ANIb and 89 % ANIm as the highest average nucleotide identity (ANI) values with B. elkanii USDA 76^T. Although CI-1B^T, CI-14A, CI-19D and CI-41S shared similar phenotypic and metabolic properties, growth of CI-41S was slower in/on various media. Symbiotic efficacy varied significantly between isolates, with CI-1B^T and CI-41S scoring on the C. cajan ‘Light-Brown’ landrace as the most and least proficient bacteria, respectively. Also proficient on Vigna radiata (mung bean), Vigna unguiculata (cowpea, niébé) and additional C. cajan cultivars, CI-1B^T represents a potential bioinoculant adapted to local soil conditions and capable of fostering the growth of diverse legume crops in Côte d'Ivoire. Given the data presented here, we propose the 19 C. cajan isolates to belong to a novel species called Bradyrhizobium ivorense sp. nov., with CI-1B^T (=CCOS 1862^T=CCMM B1296^T) as a type strain.

Rhizobium terrae sp. nov., Isolated from an Oil-Contaminated Soil in China

A Gram-stain-negative, facultative aerobic, non-spore-forming, non-motile, non-flagellated, rod-shaped bacterium, designated strain NAU-18^T was isolated from an oil-contaminated soil in China. Strain NAU-18^T could grow at 10-42 °C (optimum, 30 °C), at pH 5.0-8.0 (optimum, 7.0) and in the presence of 0-2.0% (w/v) NaCl (optimum, 0.5% NaCl in R2A). The predominant fatty acids were C_18:1ω7c (71.2%) and Summed feature 2 (5.1%), representing 76.3% of the total fatty acids. The major respiratory quinones were Q9 and Q10. The DNA G + C content of strain NAU-18^T was 61.4 mol% based on its draft genome sequence. Genome annotation of strain NAU-18^T predicted the presence of 6668 genes, of which 6588 are coding proteins and 80 are RNA genes. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain NAU-18^T was a member of the genus Rhizobium and showed 96.93% (with 93.2% coverage) and 96.81% (with 100% coverage) identities with those of Neorhizobium alkalisoli CCBAU 01393^T and Rhizobium oryzicola ZYY136^T, respectively. In the phylogenetic analysis, strain NAU-18^T and R. oryzicola ZYY136^T are consistently placed in the same branch. Strain NAU-18^T represents a novel species within the genus Rhizobium, for which the name Rhizobium terrae sp. nov. is proposed, with the type strain NAU-18^T (=KCTC 62418^T = CCTCC AB 2018075^T).

Description and complete genome sequences of Bradyrhizobium symbiodeficiens sp. nov., a non-symbiotic bacterium associated with legumes native to Canada

Four bacterial strains isolated from root nodules of soybean plants that had been inoculated with root-zone soil of either Amphicarpaea bracteata (Hog Peanut) or Desmodium canadense (Showy Tick Trefoil) growing in Canada, were previously characterized and placed in a novel lineage within the genus Bradyrhizobium. The taxonomic status of the novel strains was verified by genomic and phenotypic analyses. Phylogenetic analyses of individual and concatenated housekeeping gene sequences (atp D, gln II, rec A, gyr B and rpo B) placed all novel strains in a highly supported lineage distinct from named Bradyrhizobium species. Data for sequence similarities of concatenated housekeeping genes of novel strains relative to type strains of named species were consistent with the phylogenetic data. Average nucleotide identity values of genome sequences (84.5-93.7 %) were below the threshold value of 95-96 % for bacterial species circumscription. Close relatives to the novel strains are Bradyrhizobium amphicarpaeae, Bradyrhizobium ottawaense and Bradyrhizobium shewense. The complete genomes of strains 85S1MBT and 65S1MB consist of single chromosomes of size 7.04 and 7.13 Mbp, respectively. The genomes of both strains have a G+C content of 64.3 mol%. These strains lack a symbiosis island as well as key nodulation, nitrogen-fixation and photosystem genes. Data from various phenotypic tests including growth characteristics and carbon source utilization supported the sequence-based analyses. Based on the data presented here, the four strains represent a novel species for which the name B radyrhizobium symbiodeficiens sp. nov., is proposed, with 85S1MBT (=LMG 29937T=HAMBI 3684T) as the type strain.

Bradyrhizobium frederickii sp. nov., a nitrogen-fixing lineage isolated from nodules of the caesalpinioid species Chamaecrista fasciculata and characterized by tolerance to high temperature in vitro

The symbioses between legumes and nitrogen-fixing rhizobia make the greatest contribution to the global nitrogen input via the process of biological nitrogen fixation (BNF). Bradyrhizobium stands out as the main genus nodulating basal Caesalpinioideae. We performed a polyphasic study with 11 strains isolated from root nodules of Chamaecristafasciculata, an annual multi-functional native legume of the USA. In the 16S rRNA gene phylogeny the strains were clustered in the Bradyrhizobium japonicumsuperclade. The results of analysis of the intergenic transcribed spacer (ITS) indicated less than 89.9 % similarity to other Bradyrhizobium species. Multilocus sequence analysis (MLSA) with four housekeeping genes (glnII, gyrB, recA and rpoB) confirmed the new group, sharing less than 95.2 % nucleotide identity with other species. The MLSA with 10 housekeeping genes (atpD, dnaK, gap, glnII, gltA, gyrB, pnp, recA, rpoB and thrC) indicated Bradyrhizobium daqingense as the closest species. Noteworthy, high genetic diversity among the strains was confirmed in the analyses of ITS, MLSA and BOX-PCR. Average nucleotide identity and digital DNA-DNA hybridization values were below the threshold of described Bradyrhizobium species, of 89.7 and 40 %, respectively. In the nifH and nodC phylogenies, the strains were grouped together, but with an indication of horizontal gene transfer, showing higher similarity to Bradyrhizobium arachidis and Bradyrhizobium forestalis. Other phenotypic, genotypic and symbiotic properties were evaluated, and the results altogether support the description of the CNPSo strains as representatives of the new species Bradyrhizobiumfrederickii sp. nov., with CNPSo 3426^T (=USDA 10052^T=U686^T=CL 20^T) as the type strain.

Rhizobium deserti sp. Nov Isolated from Biological Soil Crusts Collected at Mu Us Sandy Land, China

A novel gram-negative, aerobic, non-spore-forming, rod-shaped, and non-nitrogen-fixing bacterium, named SPY-1^T, was isolated from biological soil crusts collected at Mu Us Sandy Land, China. Based on 16S rRNA sequence similarity, strain SPY-1^T was most closely related to Neorhizobium alkalisoli CCTCC AB 2014138^T (98.7%), Neorhizobium huautlense CGMCC 1.2538^T (98.6%), Neorhizobium galegae DSM 11542^T (98.4%), Rhizobium wenxiniae 166^T (97.9%), and Rhizobium smilacinae CCTCC AB 2013016^T (97.5%). Phylogenetic analysis based on 16S rRNA sequencing and multilocus sequence analysis of partial sequences of atpD-glnII-glnA-recA-ropD-thrC housekeeping genes both indicated that strain SPY-1^T was a member of the genus Rhizobium. The draft genome of strain SPY-1^T was 4.75 Mb in size, and the G + C content was 60.0%. The average nucleotide identity (ANI) values to N. alkalisoli CCTCC AB 2014138^T and R. smilacinae CCTCC AB 2013016^T were both 84.0%. The digital DNA-DNA hybridization (dDDH) values to N. alkalisoli CCTCC AB 2014138^T and R. smilacinae CCTCC AB 2013016^T were 20.9% and 20.2%, respectively. The major cellular fatty acids were summed feature 8 (C_18:1ω7c and/or C_18:1ω6c) and C_16:0. Based on the data from chemotaxonomic, phylogenetic, and phenotypic evidence, strain SPY-1^T represents a novel species in the genus Rhizobium, for which the name Rhizobium deserti sp. nov. is proposed. The type strain is SPY-1^T (= ACCC 61627^T = JCM 33732^T).

Two Novel Genomospecies in the Agrobacterium tumefaciens Species Complex Associated with Rose Crown Gall

In this study, we explored the pathogenicity and phylogenetic position of Agrobacterium spp. strains isolated from crown gall tissues on annual, perennial, and ornamental plants in Iran. Of the 43 strains studied, 10 strains were identified as Allorhizobium vitis (formerly Agrobacterium vitis) using the species-specific primer pair PGF/PGR. Thirty-three remaining strains were studied using multilocus sequence analysis of four housekeeping genes (i.e., atpD, gyrB, recA, and rpoB), from which seven strains were identified as A. larrymoorei and one strain was identified as A. rubi (Rer); the remaining 25 strains were scattered within the A. tumefaciens species complex. Two strains were identified as genomospecies 1 (G1), seven strains were identified as A. radiobacter (G4), seven strains were identified as A. deltaense (G7), two strains were identified as A. nepotum (G14), and one strain was identified as "A. viscosum" (G15). The strains Rnr, Rnw, and Rew as well as the two strains OT33 and R13 all isolated from rose and the strain Ap1 isolated from apple were clustered in three atypical clades within the A. tumefaciens species complex. All but eight strains (i.e., Nec10, Ph38, Ph49, fic9, Fic72, R13, OT33, and Ap1) were pathogenic on tomato and sunflower seedlings in greenhouse conditions, whereas all but three strains (i.e., fic9, Fic72, and OT33) showed tumorigenicity on carrot root discs. The phylogenetic analysis and nucleotide diversity statistics suggested the existence of two novel genomospecies within the A. tumefaciens species complex, which we named "G19" and "G20." Hence, we propose the strains Rew, Rnw, and Rnr as the members of "G19" and the strains R13 and OT33 as the members of G20, whereas the phylogenetic status of the atypical strain Ap1 remains undetermined.

Description and complete genome sequence of Bradyrhizobium amphicarpaeae sp. nov., harbouring photosystem and nitrogen-fixation genes

A bacterial strain, designated 39S1MBT, isolated from a root nodule of a soybean plant that had been inoculated with root-zone soil of Amphicarpaea bracteata (hog peanut) growing in Canada, was previously characterized and placed in a novel lineage within the genus Bradyrhizobium. The taxonomic status of strain 39S1MBT was verified by genomic and phenotypic analyses. Phylogenetic analyses of individual and concatenated protein-encoding gene sequences (atpD, glnII, recA, gyrB and rpoB) placed 39S1MBT in a lineage distinct from named species. Data for sequence similarities of concatenated genes relative to type strains of named species supported the phylogenetic data. Average nucleotide identity values of genome sequences (84.5-91.7 %) were well below the threshold value for bacterial species circumscription. Based on these data, Bradyrhizobium ottawaense OO99T and Bradyrhizobium shewense ERR11T are close relatives of 39S1MBT. The complete genome of 39S1MBT consists of a single 7.04 Mbp chromosome without a symbiosis island; G+C content is 64.7 mol%. Present in the genome are key photosystem and nitrogen-fixation genes, but not nodulation and type III secretion system genes. Sequence analysis of the nitrogen fixation gene, nifH, placed 39S1MBT in a novel lineage distinct from named Bradyrhizobium species. Data for phenotypic tests including growth characteristics and carbon source utilization supported the sequence-based analyses. Based on the data presented here, a novel species with the name Bradyrhizobium amphicarpaeae sp. nov. is proposed with 39S1MBT (=LMG 29934T=HAMBI 3680T) as the type strain.

Bradyrhizobium nanningense sp. nov., Bradyrhizobium guangzhouense sp. nov. and Bradyrhizobium zhanjiangense sp. nov., isolated from effective nodules of peanut in Southeast China

Nine slow-growing rhizobia isolated from effective nodules on peanut (Arachis hypogaea) were characterized to clarify the taxonomic status using a polyphasic approach. They were assigned to the genus Bradyrhizobium on the basis of 16S rRNA sequences. MLSA of concatenated glnII-recA-dnaK genes classified them into three species represented by CCBAU 53390^T, CCBAU 51670^T and CCBAU 51778^T, which presented the closest similarity to B. guangxiense CCBAU 53363^T, B. guangdongense CCBAU 51649^T and B. manausense BR 3351^T, B. vignae 7-2^T and B. forestalis INPA 54B^T, respectively. The dDDH (digital DNA-DNA hybridization) and ANI (Average Nucleotide Identity) between the genomes of the three representative strains and type strains for the closest Bradyrhizobium species were less than 42.1% and 91.98%, respectively, below the threshold of species circumscription. Effective nodules could be induced on peanut and Lablab purpureus by all representative strains, while Vigna radiata formed effective nodules only with CCBAU 53390^T and CCBAU 51778^T. Phenotypic characteristics including sole carbon sources and growth features supported the phylogenetic results. Based on the genotypic and phenotypic features, strains CCBAU 53390^T, CCBAU 51670^T and CCBAU 51778^T are designated the type strains of three novel species, for which the names Bradyrhizobium nanningense sp. nov., Bradyrhizobium guangzhouense sp. nov. and Bradyrhizobium zhanjiangense sp. nov. are proposed, respectively.

Rhizobium chutanense sp. nov., isolated from root nodules of Phaseolus vulgaris in China

Two Gram-stain-negative, rod-shaped bacterial strains (C5T and C16), isolated from root nodules of Phaseolus vulgaris L. in Jiangxi Province, PR China, were characterized by using a polyphasic taxonomical approach. The phylogenetic analysis of the 16S rRNA gene and three concatenated housekeeping genes (recA-glnII-atpD) revealed that C5T and C16 were members of the genus Rhizobium, yet were distinct from known species. The case for strain C5T representing a novel species was supported by genomic results. Pairwise digital DNA-DNA hybridization and average nucleotide identity values were much lower than the proposed and generally accepted species boundaries. The genome-based phylogenetic tree reconstructed by using the up-to-date bacterial core gene set consisting of 92 genes showed that the strains formed a monophyletic branch, further supporting this result. The symbiotic genes of nodC and nifH were identified in both strains; each could nodulate Phaseolus vulgaris and Glycine max but not Leucaena leucocephala, Pisum sativum or Medicago sativa plants. Major cellular fatty acids of C5T were summed feature 8 (C18 : 1 ω7c/C18 : 1 ω6c; 58.8 %), C18 : 1 ω7c 11-methyl (14.2 %) and C18 : 0 (8.1 %). The DNA G+C content of C5T was 61.4 mol%. Based on these genomic, chemotaxonomic and phenotypic characteristics, we propose a novel species: Rhizobium chutanense sp. nov. The type strain is C5T (=CCTCC AB 2018143T=LMG 30777T).

Microvirga calopogonii sp. nov., a novel alphaproteobacterium isolated from a root nodule of Calopogonium mucunoides in Southwest China

In this study, a Gram-negative, rod-shaped, and non-spore-forming bacterium, which was designated as strain CCBUA 65841^T, was isolated from a root nodule of Calopogonium mucunoides grown in Yunan Province of China. The sequence alignment results of 16S rRNA and four housekeeping genes (including gyrB, recA, dnaK and rpoB) indicated the isolated strain is a member of the genus Microvirga, closely related to Microvirga lotononidis WSM3557^T. In addition, results of genome average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) had revealed the lower values (ANI ≤ 88.72%, dDDH ≤ 39.5%) between strain CCABU 65841^T and other related Microvirga species. The genome of the novel strain exhibits a G + C content of 64.48% and contains 7296 protein-coding genes and 93 RNA genes. The major polar lipids were found to be phosphatidylcholine and phosphatidylethanolamine. The predominant cellar fatty acids were identified to be C16:0, C18:0, C19:0 _cyclo ω8c, summed feature 2, summed feature 3 and summed feature 8. Moreover, menaquinone 8 (MK-8) was detected to be the predominant quinone. Based on the phylogenetic and phenotypic dissimilarity, a novel species Microvirga calopogonii sp. nov. is proposed with the type strain CCABU 65841^T (= LMG 25488 ^T = HAMBI 3033^T).

Rhizobium album sp. nov., isolated from a propanil-contaminated soil

A novel Gram-stain negative, facultatively anaerobic, non-spore-forming, motile and rod-shaped bacterium (NS-104^T) was isolated from a propanil-contaminated soil in Nanjing, China. Growth occurred at pH 5.0-9.0 (optimum 6.0), 16-37 °C (optimum 30 °C) and in the presence of 0-2.0% (w/v) NaCl (optimum, without NaCl). Strain NS-104^T showed high 16S rRNA gene sequence identity to Rhizobium azooxidifex DSM 100211^T (96.7%). The phylogenetic analysis of the 16S rRNA gene as well as the housekeeping genes recA, atpD and glnA demonstrated that strain NS-104^T belongs to the genus Rhizobium. Strain NS-104^T did not form nodules on six different legumes, and the nodD, nodC and nifH genes were neither amplified by PCR nor found in the draft genome of strain NS-104^T. The sole respiratory quinone was ubiquinone Q-10. The polar lipid profile included the major amounts phosphatidylmonomethylethanolamine, phosphatidylglycerol and moderate amounts of phosphatidylethanolamine, phosphatidylcholine, diphosphatidylglycerol and unidentified aminolipids. The major cellular fatty acids were C_18:1ω7c (39.6%), C_19:0 cyclo ω8c (29.8%) and C_16:0 (11.5%). The G + C content of strain NS-104^T was 61.9 mol%. Strain NS-104^T therefore represents a new species, for which the name Rhizobium album sp. nov. is proposed, with the type strain NS-104^T (= KCTC 62327^T = CCTCC AB 2017250^T).

Presence of Cu-Type (NirK) and cd1-Type (NirS) Nitrite Reductase Genes in the Denitrifying Bacterium Bradyrhizobium nitroreducens sp. nov

Nitrite reductase is a key enzyme for denitrification. There are two types of nitrite reductases: copper-containing NirK and cytochrome cd₁-containing NirS. Most denitrifiers possess either nirK or nirS, although a few strains been reported to possess both genes. We herein report the presence of nirK and nirS in the soil-denitrifying bacterium Bradyrhizobium sp. strain TSA1^T. Both nirK and nirS were identified and actively transcribed under denitrification conditions. Based on physiological, chemotaxonomic, and genomic properties, strain TSA1^T (=JCM 18858^T=KCTC 62391^T) represents a novel species within the genus Bradyrhizobium, for which we propose the name Bradyrhizobium nitroreducens sp. nov.

Mesorhizobium wenxiniae sp. nov., isolated from chickpea (Cicer arietinum L.) in China

Three chickpea rhizobial strains (WYCCWR 10195^T=S1-3-7, WYCCWR 10198=S1-4-3 and WYCCWR 10200=S1-5-1) isolated from Northwest China formed a group affiliated to Mesorhizobium based on 16S rRNA gene sequence comparison. To clarify their species status, multilocus sequence analysis and average nucleotide identity (ANI) values of whole genome sequences between the novel group and the type strains of the related species were further performed. Similarities of 95.7-96.6 % in the concatenated sequences of atpD-recA-glnII and 91.9-93.1 % of ANI values to the closest-related species Mesorhizobium muleiense, Mesorhizobium mediterraneum and Mesorhizobium temperatum demonstrated the novel group a unique genospecies. The most abundant fatty acid in cells of WYCCWR 10195^T were C19 : 0 cyclo ω8c (51.4 %), followed by C18 : 1 ω7c 11-methyl (9.5 %) and C16 : 0 (9.3 %). Its genome size was 6.37 Mbp, comprising 6633 predicted genes with a DNA G+C content of 61.9 mol%. The similarities of 99.0-99.8 % for the nodC gene and 98.3-99.44 % for the nifH gene to those of the chickpea rhizobial species and nodulation with Cicer arietinum L. confirmed the strains of the new genospecies as symbiovar ciceri. The weak utilization of most of the tested sugars/organic acids and non-utilization of l(+)-rhamnose, l-cysteine and l-glycine as sole carbon source, tolerance to 1 % (w/v) NaCl, resistance to 5 µg ml^-1 chloromycetin and non-hydrolysis of l-tyrosine distinguished the novel group from the related species and supported this group as a novel species, for which the name Mesorhizobium wenxiniae sp. nov. is proposed, with WYCCWR 10195^T (=S1-3-7=HAMBI 3692^T=LMG 30254^T) as the type strain.

Mesorhizobium zhangyense sp. nov., isolated from wild Thermopsis lanceolate in northwestern China

A Gram-stain-negative strain, 23-3-2^T, was isolated from a nodule of Thermopsis lanceolate grown in Northwest China. Phylogenetic analysis of 16S rRNA gene sequence showed that the strain was closely related to Mesorhizobium camelthorni CCNWXJ 40-4^T and M. alhagi CCNWXJ 12-2^T having 98.0 and 97.9% similarities, respectively. Phylogenetic analysis based on the protein-coding genes atpD and glnA showed lower similarity with the same closely related species (94.5 and 89.9%, respectively), which suggest that 23-3-2^T strain represents a distinctly delineated genospecies of the genus Mesorhizobium. The 23-3-2^T strain grew at 20-37 °C temperature (optimum 28 °C) and 5.0-9.0 pH range (optimum pH 7.0). The cells contained Q-10 as the sole respiratory quinone and 18:1ω7c (24.56%) as the major cellular fatty acid. The DNA relatedness between the strain 23-3-2^T and the two reference strains was 39-44%. Based on the phenotypic, chemotaxonomic and phylogenetic properties, strain 23-3-2^T represents a novel species of the genus Mesorhizobium, for which the name Mesorhizobium zhangyense sp. nov. is proposed. The type strain is 23-3-2^T (= CGMCC 1.15528^T = NBRC 112337^T). The respective DPD Taxon Number is TA00147.

Polyphasic taxonomic characterisation of a novel strain as Pararhizobium haloflavum sp. nov., isolated from soil samples near a sewage treatment tank

A Gram-stain negative, aerobic, motile and ovoid- to rod-shaped bacteria strain, designated XC0140^T, was isolated from soil samples near the sewage treatment tank of a chemical factory in Zhejiang Province, China, and subjected to polyphasic taxonomic investigation. Strain XC0140^T grew at 10-37 °C and pH 6.0-9.0 (optimum, 35 °C and pH 7.5) and with 0-17% (w/v) NaCl (optimum, 1%). According to phylogenetic analysis based on 16S rRNA gene sequences, strain XC0140^T was assigned to the genus Pararhizobium with high 16S rRNA gene sequence similarity of 95.97% to "Pararhizobium helanshanense CCNWQTX14^T", followed by Pararhizobium sphaerophysae CCNWGS0238^T (95.95%). Chemotaxonomic analysis showed that strain XC0140^T contains ubiquinone-10 as the predominant respiratory quinone and possessed summed feature 8 (comprising C_{18: 1} ω7c and/or ω6c), 11-methyl C_18:1 ω7c, C_{18: 0} and C_{16: 0} as predominant forms of fatty acids. The polar lipids of strain XC0140^T consisted of seven phospholipids (PL), two aminolipids (AL), one glycolipid (GL) and three unidentified lipids (L1, L2 and L3). The DNA G+C content was 62.7 mol%. Based on the polyphasic taxonomic characterization, strain XC0140^T is considered to represent a novel species of the genus Pararhizobium, for which the name Pararhizobium haloflavum sp. nov. is proposed. (type strain XC0140^T = MCCC 1K03228^T = KCTC 52582^T).

Studies on lipid A isolated from Phyllobacterium trifolii PETP02T lipopolysaccharide

The structure of lipid A from lipopolysaccharide of Phyllobacterium trifolii PETP02T, a nitrogen-fixing symbiotic bacterium, was studied. It was found that the lipid A backbone was composed of two 2,3-diamino-2,3-dideoxy-D-glucose (GlcpN3N) residues connected by a β-(1 → 6) glycosidic linkage, substituted by galacturonic acid (GalpA) at position C-1 and partly decorated by a phosphate residue at C-4' of the non-reducing GlcpN3N. Both diaminosugars were symmetrically substituted by 3-hydroxy fatty acids (14:0(3-OH) and 16:0(3-OH)). Ester-linked secondary acyl residues [i.e. 19:0cyc and 28:0(27-OH) or 28:0(27-4:0(3-OMe))] were located in the distal part of lipid A. A high similarity between the lipid A of P. trifolii and Mesorhizobium was observed and discussed from the perspective of the genetic context of both genomes.

Bradyrhizobium sacchari sp. nov., a legume nodulating bacterium isolated from sugarcane roots

Members of the genus Bradyrhizobium are well-known as nitrogen-fixing microsymbionts of a wide variety of leguminous species, but they have also been found in different environments, notably as endophytes in non-legumes such as sugarcane. This study presents a detailed polyphasic characterization of four Bradyrhizobium strains (type strain BR 10280T), previously isolated from roots of sugarcane in Brazil. 16S rRNA sequence analysis, multilocus sequence analysis (MLSA) and analysis of the 16S-23S rRNA internal transcribed spacer showed that these strains form a novel clade close to, but different from B. huanghuaihaiense strain CCBAU 23303T. Average nucleotide identity (ANI) analyses confirmed that BR 10280T represents a novel species. Phylogenetic analysis based on nodC gene sequences also placed the strains close to CCBAU 23303T, but different from this latter strain, the sugarcane strains did not nodulate soybean, although they effectively nodulated Vigna unguiculata, Cajanus cajan and Macroptilium atropurpureum. Physiological traits are in agreement with the placement of the strains in the genus Bradyrhizobium as a novel species for which the name Bradyrhizobium sacchari sp. nov. is proposed.

Electrophoretic profiles of lipopolysaccharides from Rhizobium strains nodulating Pisum sativum do not reflect phylogenetic relationships between these strains

Rhizobia that nodulate peas comprise a heterogeneous group of bacteria. The aim of this study was to investigate the relationship between phylogeny and electrophoretic and hydroxy fatty acid lipopolysaccharide (LPS) profiles of pea microsymbionts. Based on amplified fragment length polymorphism (AFLP) fingerprinting data, the pea microsymbionts were grouped into two clusters distinguished at 58% similarity level. Based on the concatenated 16S rRNA, recA, and atpD housekeeping gene data, the microsymbionts appeared to be most closely related to Rhizobium leguminosarum biovars viciae and trifolii. Applying cluster analysis to their LPS electrophoretic profiles, the strains were assigned to two major groups with different banding patterns. All hydroxy fatty acids common to R. leguminosarum and R. etli were detected in each examined strain. Differences in the proportions of 3- to ω-1 hydroxy fatty acids allowed us to distinguish two groups of strains. This classification did not overlap with one based on LPS electrophoretic profiles. No clear correlation was apparent between the genetic traits and LPS profiles of the pea nodule isolates.