Genetic variation in symbiotic islands of natural variant strains of soybean Bradyrhizobium japonicum and Bradyrhizobium diazoefficiens differing in competitiveness and in the efficiency of nitrogen fixation.

Soybean is the most important legume cropped worldwide and can highly benefit from the biological nitrogen fixation (BNF) process. Brazil is recognized for its leadership in the use of inoculants and two strains, Bradyrhizobium japonicum CPAC 15 (=SEMIA 5079) and Bradyrhizobium diazoefficiens CPAC 7 (=SEMIA 5080) compose the majority of the 70 million doses of soybean inoculants commercialized yearly in the country. We studied a collection of natural variants of these two strains, differing in properties of competitiveness and efficiency of BNF. We sequenced the genomes of the parental strain SEMIA 566 of B. japonicum, of three natural variants of this strain (S 204, S 340 and S 370), and compared with another variant of this group, strain CPAC 15. We also sequenced the genome of the parental strain SEMIA 586 of B. diazoefficiens, of three natural variants of this strain (CPAC 390, CPAC 392 and CPAC 394) and compared with the genome of another natural variant, strain CPAC 7. As the main genes responsible for nodulation (nod, noe, nol) and BNF (nif, fix) in soybean Bradyrhizobium are located in symbiotic islands, our objective was to identify genetic variations located in this region, including single nucleotide polymorphisms (SNPs) and insertions and deletions (indels), that could be potentially related to their different symbiotic phenotypes. We detected 44 genetic variations in the B. japonicum strains and three in B. diazoefficiens. As the B. japonicum strains have gone through a longer period of adaptation to the soil, the higher number of genetic variations could be explained by survival strategies under the harsh environmental conditions of the Brazilian Cerrado biome. Genetic variations were detected in genes enconding proteins such as a dephospho-CoA kinase, related to the CoA biosynthesis; a glucosamine-fructose-6-phosphate aminotransferase, key regulator of the hexosamine biosynthetic pathway; a LysR family transcriptional regulator related to nodulation genes; and NifE and NifS proteins, directly related to the BNF process. We suggest potential genetic variations related to differences in the symbiotic phenotypes.

Microbiological quality analysis of inoculants based on Bradyrhizobium spp. and Azospirillum brasilense produced "on farm" reveals high contamination with non-target microorganisms.

The use of inoculants carrying diazotrophic and other plant growth-promoting bacteria plays an essential role in the Brazilian agriculture, with a growing use of microorganism-based bioproducts. However, in the last few years, some farmers have multiplied microorganisms in the farm, known as "on farm" production, including inoculants of Bradyrhizobium spp. for soybean (Glycine max L. Merrill.) and Azospirillum brasilense for corn (Zea mays L.) or co-inoculation in soybean. The objective was to assess the microbiological quality of such inoculants concerning the target microorganisms and contaminants. In the laboratory, 18 samples taken in five states were serial diluted and spread on culture media for obtaining pure and morphologically distinct colonies of bacteria, totaling 85 isolates. Molecular analysis based on partial sequencing of the 16S rRNA gene revealed 25 genera of which 44% harbor species potentially pathogenic to humans; only one of the isolates was identified as Azospirillum brasilense, whereas no isolate was identified as Bradyrhizobium. Among 34 isolates belonging to genera harboring species potentially pathogenic to humans, 12 had no resistance to antibiotics, six presented intrinsic resistance, and 18 presented non-intrinsic resistance to at least one antibiotic. One of the samples analyzed with a shotgun-based metagenomics approach to check for the microbial diversity showed several genera of microorganisms, mainly Acetobacter (~ 32% of sequences) but not the target microorganism. The samples of inoculants produced on farm were highly contaminated with non-target microorganisms, some of them carrying multiple resistances to antibiotics.

Molecular diversity of rhizobia-nodulating native Mimosa of Brazilian protected areas.

Symbiotic Paraburkholderia have been increasingly studied in the past 20 years, especially when associated with Mimosa; however, studies with native/endemic species are still scarce. In this study, thirty strains were isolated from root nodules of native Mimosa paranapiacabae and M. micropteris in two locations of the Campos Gerais. The BOX-PCR fingerprinting revealed high genomic diversity, and the 16S rRNA phylogeny clustered the strains in three distinct groups (GI, GII, GIII), with one strain occupying an isolated position. Phylogenetic analysis with four concatenated housekeeping genes (atpD + gltB + gyrB + recA) confirmed the same clusters of 16S rRNA, and the closest species were P. nodosa BR 3437T and P. guartelaensis CNPSo 3008T; this last one isolated from another Mimosa species of the Campos Gerais. The phylogenies of the symbiotic genes nodAC and nifH placed all strains in a well-supported branch with the other species of the symbiovar mimosae. The phylogenetic analyses indicated that the strains represent novel lineages of sv. mimosae and that endemic Mimosa coevolved with indigenous Paraburkholderia in their natural environments.

Phylogeny of symbiotic genes reveals symbiovars within legume-nodulating Paraburkholderia species.

Bacteria belonging to the genus Paraburkholderia are capable of establishing symbiotic relationships with plants belonging to the Fabaceae (=Leguminosae) family and fixing the atmospheric nitrogen in specialized structures in the roots called nodules, in a process known as biological nitrogen fixation (BNF). In the nodulation and BNF processes several bacterial symbiotic genes are involved, but the relations between symbiotic, core genes and host specificity are still poorly studied and understood in Paraburkholderia. In this study, eight strains of nodulating nitrogen-fixing Paraburkholderia isolated in Brazil, together with described species and other reference strains were used to infer the relatedness between core (16S rDNA, recA) and symbiotic (nod, nif, fix) genes. The diversity of genes involved in the nodulation (nodAC) and nitrogen fixation (nifH) abilities was investigated. Only two groups, one containing three Paraburkholderia species symbionts of Mimosa, and another one with P. ribeironis strains presented similar phylogenetic patterns in the analysis of core and symbiotic genes. In three other groups events of horizontal gene transfer of symbiotic genes were detected. Paraburkholderia strains with available genomes were used in the complementary analysis of nifHDK and fixABC and confirmed well-defined phylogenetic positions of symbiotic genes. In all analyses of nod, nif and fix genes the strains were distributed into five clades with high bootstrap support, allowing the proposal of five symbiovars in nodulating nitrogen-fixing Paraburkholderia, designated as mimosae, africana, tropicalis, atlantica and piptadeniae. Phylogenetic inferences within each symbiovar are discussed.

Genetic diversity of Agrobacterium species isolated from nodules of common bean and soybean in Brazil, Mexico, Ecuador and Mozambique, and description of the new species Agrobacterium fabacearum sp. nov.

Agrobacterium strains are associated with soil, plants and animals, and known mainly by their pathogenicity. We studied 14 strains isolated from nodules of healthy soybean and common bean plants in Brazil, Mexico, Ecuador and Mozambique. Sequence analysis of the 16S rRNA gene positioned the strains as Agrobacterium, but with low phylogenetic resolution. Multilocus sequence analysis (MLSA) of three partial housekeeping genes (glnII, gyrB and recA) positioned the strains in four distinct clades, with Agrobacterium pusense, Agrobacterium deltaense, Agrobacterium radiobacter and Agrobacterium sp. genomospecies G1. Analysis by BOX-PCR revealed high intraspecies diversity. Genomic analysis of representative strains of the three clades indicated that they carry the protelomerase telA gene, and MLSA analysis with six complete housekeeping genes (atpD, glnII, gyrB, recA, rpoB and thrC), as well as average nucleotide identity (less than 90 % with closest species) and digital DNA-DNA hybridization (less than 41 % with closest species) revealed that strain CNPSo 675T and Agrobacterium sp. genomospecies G1 compose a new species. Other phenotypic and genotypic characteristics were determined for the new clade. Although not able to re-nodulate the host, we hypothesize that several strains of Agrobacterium are endophytes in legume nodules, where they might contribute to plant growth. Our data support the description of the CNPSo 675T and Agrobacterium sp. genomospecies G1 strains as a new species, for which the name Agrobacterium fabacearum is proposed. The type strain is CNPSo 675T (=UMR 1457T=LMG 31642T) and is also deposited in other culture collections.

Paraburkholderia atlantica sp. nov. and Paraburkholderia franconis sp. nov., two new nitrogen-fixing nodulating species isolated from Atlantic forest soils in Brazil.

A polyphasic study was conducted with 11 strains trapped by Mimosa pudica and Phaseolus vulgaris grown in soils of the Brazilian Atlantic Forest. In the phylogenetic analysis of the 16S rRNA gene, one clade of strains (Psp1) showed higher similarity with Paraburkholderia piptadeniae STM7183T (99.6%), whereas the second (Psp6) was closely related to Paraburkholderia tuberum STM678T (99%). An MLSA (multilocus sequence analysis) with four (recA, gyrB, trpB and gltB) housekeeping genes placed both Psp1 and Psp6 strains in new clades, and BOX-PCR profiles indicated high intraspecific genetic diversity within each clade. Values of digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) of the whole genome sequences were of 56.9 and 94.4% between the Psp1 strain CNPSo 3157T and P. piptadeniae; and of 49.7% and 92.7% between the Psp6 strain CNPSo 3155T and P. tuberum, below the threshold for species delimitation. In the nodC analysis, Psp1 strains clustered together with P. piptadeniae, while Psp6 did not group with any symbiotic Paraburkholderia. Other phenotypic, genotypic and symbiotic properties were evaluated. The polyphasic analysis supports that the strains represent two novel species, for which the names Paraburkholderia franconis sp. nov. with type strain CNPSo 3157T (= ABIP 241, = LMG 31644) and Paraburkholderia atlantica sp. nov. with type strain CNPSo 3155T (= ABIP 236, = LMG 31643) are proposed.

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 3426T (=USDA 10052T=U686T=CL 20T) as the type strain.

Paraburkholderia guartelaensis sp. nov., a nitrogen-fixing species isolated from nodules of Mimosa gymnas in an ecotone considered as a hotspot of biodiversity in Brazil.

A polyphasic approach was used to infer the phylogenetic position of six nitrogen-fixing symbiotic bacteria isolated from Mimosa gymnas nodules grown in an ecotone between the Brazilian biomes of Atlantic Forest and Cerrado, considered as a hotspot of biodiversity. The 16S rRNA gene phylogeny indicated the highest similarity with Paraburkholderia oxyphila (98.7-98.9%), but similar values were found with other Paraburkholderia species. The multilocus sequence analysis (MLSA) of five (recA, gyrB, trpB, gltB, and atpD) housekeeping genes indicated that the CNPSo strains represent a novel lineage, sharing less than 95.7% of nucleotide identity (NI) with other Paraburkholderia species, being more closely related to P. nodosa. Genome parameters were analyzed for strain CNPSo 3008T, and DNA-DNA hybridization revealed a maximum of 55.9% of DNA-DNA relatedness with P. nodosa, while average nucleotide identity with the two closest species was of 93.84% with P. nodosa and of 87.93% with P. mimosarum, both parameters confirming that the strain represents a new species. In the analysis of the nodulation nodC gene, all CNPSo strains showed the highest similarity with P. nodosa, and nodulation tests indicated host specificity with Mimosa. Other phylogenetic, physiological, and chemotaxonomic properties were evaluated. All data obtained support the description of the novel species Paraburkholderia guartelaensis sp. nov., with CNPSo 3008T (= U13000T = G29.01T) indicated as the type strain.

Bradyrhizobium niftali sp. nov., an effective nitrogen-fixing symbiont of partridge pea [Chamaecrista fasciculata (Michx.) Greene], a native caesalpinioid legume broadly distributed in the USA.

Information about the symbionts of legumes of the Caesalpinioideae subfamily is still limited, and we performed a polyphasic approach with three Bradyrhizobium strains-CNPSo 3448T, CNPSo 3394 and CNPSo 3442-isolated from Chamaecrista fasciculata, a native legume broadly distributed in the USA. In the phylogenetic analysis of both the 16S rRNA gene and the intergenic transcribed spacer, the CNPSo strains were clustered within the Bradyrhizobium japonicumsuperclade. Multilocus sequence analysis with six housekeeping genes-glnII, gyrB, recA, rpoB, atpD and dnaK-indicated that Bradyrhizobium diazoefficiens is the closest species, with 83 % of nucleotide identity. In the genome analyses of CNPSo 3448T, average nucleotide identity and digital DNA-DNA hybridization results confirmed higher similarity with B. diazoefficiens, with values estimated of 93.35 and 51.50 %, respectively, both below the threshold of the same species, confirming that the CNPSo strains represent a new lineage. BOX-PCR profiles indicated high intraspecific genetic diversity between the CNPSo strains. In the analyses of the symbiotic genes nodC and nifH the CNPSo strains were clustered with Bradyrhizobium arachidis, Bradyrhizobium forestalis, Bradyrhizobium cajani, Bradyrhizobium kavangense and Bradyrhizobium vignae, indicating a different phylogenetic history compared to the conserved core genes. Other physiological (C utilization, tolerance to antibiotics and abiotic stresses), chemical (fatty acid profile) and symbiotic (nodulation host range) properties were evaluated and are described. The data from our study support the description of the CNPSo strains as the novel species Bradyrhizobiumniftali sp. nov., with CNPSo 3448T (=USDA 10051T=U687T=CL 40T) designated as the type strain.

Draft Genome Sequence of Bradyrhizobium elkanii Strain SEMIA 938, Used in Commercial Inoculants for Lupinus spp. in Brazil.

Due to its high capacity for nitrogen fixation, strain SEMIA 938 is used in commercial inoculants for lupins in Brazil. Its genome was estimated at 8,780,064 bp and indicates that it belongs to the Bradyrhizobium elkanii species, while the analysis of nodulation genes classifies the strain in the symbiovar sojae.

Mesorhizobium atlanticum sp. nov., a new nitrogen-fixing species from soils of the Brazilian Atlantic Forest biome.

Biological nitrogen fixation performed by diazotrophic bacteria is a vital process for agricultural and environmental sustainability. In recent years, bacterial classification has been based on genomic data, accelerating our understanding about the diversity, and resulting in the description of several new species. In this study, four strains (CNPSo 3140T, CNPSo 3235, CNPSo 3236 and CNPSo 3237) trapped by Phaseolus vulgaris and Mimosa pudica from soil samples of the Brazilian Atlantic Forest biome (Mata Atlântica) were submitted to polyphasic analysis to investigate their proper classification within the genus Mesorhizobium. The 16S rRNA gene phylogram showed that the strains present sequences identical to those of Mesorhizobium acaciaeand Mesorhizobium plurifarium, not allowing a clear taxonomic classification; however, when using multilocus sequence analysis methodology, the strains were grouped into a well-supported distinct clade, with <94.5 % nucleotide identity with the other species of the genus. The average nucleotide identity of CNPSo 3140T genome showed values below the threshold in relation to the closest species, of 89.75 % with Mesorhizobium plurifariumand of 88.83 % with Mesorhizobium hawassense; the digital DNA-DNA hybridization values were 39 and 37.70 % with the same species, respectively. Nodulation gene (nodC) phylogeny positioned the strains in an isolated cluster, showing greater similarity to Mesorhizobiumshonense. All data obtained in this study support the description of the novel species Mesorhizobiumatlanticum sp. nov. The type strain is CNPSo 3140T (=ABIP 206T=LMG 30305T=U1602T), isolated from a nodule of Phaseolus vulgaris.

Draft Genome Sequence of Agrobacterium deltaense Strain CNPSo 3391, Isolated from a Soybean Nodule in Mozambique.

Agrobacterium deltaense strain CNPSo 3391 was isolated from a soybean nodule in Mozambique. Its genome size was estimated at 4,926,588 bp. This isolate carries several coding sequences for stress tolerance, but no identifiable nodulation or virulence genes. Possible ecological roles of bacteria isolated from legume nodules and closely related to Agrobacterium are discussed.

Phylogenetic diversity of rhizobia nodulating native Mimosa gymnas grown in a South Brazilian ecotone.

Floristic surveys performed in "Campos Gerais" (Paraná, Brazil), an ecotone of Mata Atlântica and Cerrado biomes, highlights the richness and relative abundance of the family Fabaceae and point out the diversity and endemism of Mimosa spp. Our study reports the genetic diversity of rhizobia isolated from root nodules of native/endemic Mimosa gymnas Barneby in three areas of Guartelá State Park, an important conservation unit of "Campos Gerais". Soils of the sample areas were characterized as sandy, acid, poor in nutrients and organic matter. The genetic variability among the isolates was revealed by BOX-PCR genomic fingerprinting. Phylogeny based on 16S rRNA gene grouped the strains in a large cluster including Paraburkholderia nodosa and P. bannensis, while recA-gyrB phylogeny separated the strains in two groups: one including P. nodosa and the other without any described Paraburkholderia species. MLSA confirmed the separate position of this second group of strains within the genus Paraburkholderia and the nucleotide identity of the five concatened housekeeping genes was 95.9% in relation to P. nodosa BR 3437T. Phylogram based on symbiosis-essential nodC gene was in agreement with 16S rRNA analysis. Our molecular phylogenetic analysis support that Paraburkholderia are the main symbionts of native Mimosa in specific edaphic conditions found in South America and reveal the importance of endemic/native leguminous plants as reservoirs of novel rhizobial species.

Genome Sequence of Bradyrhizobium mercantei Strain SEMIA 6399T, Isolated from Nodules of Deguelia costata in Brazil.

SEMIA 6399T is the type strain of Bradyrhizobium mercantei, a nitrogen-fixing symbiont of Deguelia costata Its draft genome contains 8,842,857 bp with 8,246 predicted coding sequences (CDS), several related to amino acids and derivatives and to stress tolerance, with an emphasis on oxidative stress, in addition to symbiotic genes.

Bradyrhizobium mercantei sp. nov., a nitrogen-fixing symbiont isolated from nodules of Deguelia costata (syn. Lonchocarpus costatus).

Some bacteria collectively known as rhizobia can establish symbiotic relationships and the N2-fixation process with several legumes used as green manure, in pastures and for wood production. Symbionts belonging to the genus Bradyrhizobium are predominant in the tropics, and an increasing number of studies report high genetic diversity within the genus. We performed a polyphasic study with two strains belonging to the genus Bradyrhizobium- SEMIA 6399T and SEMIA 6404-isolated from root nodules of Deguelia costata (syn. Lonchocarpus costatus), an important legume native to eastern Brazil. In general, sequences of the 16S rRNA gene were highly conserved in members of the genus Bradyrhizobium, and the two strains were positioned in the Bradyrhizobiumelkanii superclade, sharing 100 % nucleotide identity with Bradyrhizobiumembrapense, Bradyrhizobiumerythrophlei and Bradyrhizobiumviridifuturi. However, multilocus sequence analysis with four housekeeping genes (dnaK, glnII, gyrB and recA) confirmed that the two strains belong to a distinct clade, sharing from 87.7 to 96.1 % nucleotide identity with related species of the genus Bradyrhizobium, being most closely related to B. viridifuturi. Average nucleotide identity of genome sequences between SEMIA 6399T and related species was lower than 92 %, below the threshold of species circumscription. nifH phylogeny clustered the SEMIA strains in a clade separated from other species of the genus Bradyrhizobium, and the nodD phylogeny revealed that SEMIA 6399T presents a more divergent sequence. Other phenotypic and genotypic traits were determined for the new group, and our data support the description of the SEMIA strains as representatives of Bradyrhizobium mercantei sp. nov.; SEMIA 6399T (=CNPSo 1165T=BR 6010T=U675T=LMG 30031T) was chosen as the type strain.

Phylogenies of symbiotic genes of Bradyrhizobium symbionts of legumes of economic and environmental importance in Brazil support the definition of the new symbiovars pachyrhizi and sojae.

Bradyrhizobium comprises most tropical symbiotic nitrogen-fixing strains, but the correlation between symbiotic and core genes with host specificity is still unclear. In this study, the phylogenies of the nodY/K and nifH genes of 45 Bradyrhizobium strains isolated from legumes of economic and environmental importance in Brazil (Arachis hypogaea, Acacia auriculiformis, Glycine max, Lespedeza striata, Lupinus albus, Stylosanthes sp. and Vigna unguiculata) were compared to 16S rRNA gene phylogeny and genetic diversity by rep-PCR. In the 16S rRNA tree, strains were distributed into two superclades-B. japonicum and B. elkanii-with several strains being very similar within each clade. The rep-PCR analysis also revealed high intra-species diversity. Clustering of strains in the nodY/K and nifH trees was identical: 39 strains isolated from soybean grouped with Bradyrhizobium type species symbionts of soybean, whereas five others occupied isolated positions. Only one strain isolated from Stylosanthes sp. showed similar nodY/K and nifH sequences to soybean strains, and it also nodulated soybean. Twenty-one representative strains of the 16S rRNA phylogram were selected and taxonomically classified using a concatenated glnII-recA phylogeny; nodC sequences were also compared and revealed the same clusters as observed in the nodY/K and nifH phylograms. The analyses of symbiotic genes indicated that a large group of strains from the B. elkanii superclade comprised the novel symbiovar sojae, whereas for another group, including B. pachyrhizi, the symbiovar pachyrhizi could be proposed. Other potential new symbiovars were also detected. The co-evolution hypotheses is discussed and it is suggested that nodY/K analysis would be useful for investigating the symbiotic diversity of the genus Bradyrhizobium.

Genome sequence of Bradyrhizobium embrapense strain CNPSo 2833T, isolated from a root nodule of Desmodium heterocarpon

Abstract Bradyrhizobium embrapense CNPSo 2833T is a nitrogen-fixing symbiont of the legume pasture Desmodium. Its draft genome contains 8,267,832 bp and 7876 CDSs. The symbiotic island includes nodulation and nitrogen fixation genes resembling the operon organization of B. japonicum. Several CDSs related to secretion proteins and stress tolerance were also identified.

Genome sequence of Bradyrhizobium embrapense strain CNPSo 2833T, isolated from a root nodule of Desmodium heterocarpon.

Bradyrhizobium embrapense CNPSo 2833T is a nitrogen-fixing symbiont of the legume pasture Desmodium. Its draft genome contains 8,267,832bp and 7876 CDSs. The symbiotic island includes nodulation and nitrogen fixation genes resembling the operon organization of B. japonicum. Several CDSs related to secretion proteins and stress tolerance were also identified.

Genome Sequence of Paraburkholderia nodosa Strain CNPSo 1341, a N2-Fixing Symbiont of the Promiscuous Legume Phaseolus vulgaris.

Paraburkholderia nodosa CNPSo 1341 is a N2-fixing symbiont of Phaseolus vulgaris isolated from an undisturbed soil of the Brazilian Cerrado. Its draft genome contains 8,614,032 bp and 8,068 coding sequences (CDSs). Nodulation and N2-fixation genes were clustered in the genome that also contains several genes of secretion systems and quorum sensing.