RESUMO
The actinobacterium Arthrobacter sp. UMCV2 promotes plant growth through the emission of N,N-dimethylhexadecilamine (DMHDA). The Medicago-Sinorhizobium nodulation has been employed to study symbiotic nitrogen fixation by rhizobia in nodulating Fabaceae. Herein, we isolated three Sinorhizobium medicae strains that were used to induce nodules in Medicago truncatula. The co-inoculation of M. truncatula with Arthrobacter sp. strain UMCV2 produced a higher number of effective nodules than inoculation with only Sinorhizobium strains. Similarly, the exposure of inoculated M. truncatula to DMHDA produced a greater number of effective nodules compared to non-exposed plants. Thus, we conclude that Arthrobacter sp. UMCV2 promotes nodulation, and propose that this effect is produced, at least partly, via DMHDA emission.
Assuntos
Arthrobacter , Medicago truncatula , Medicago truncatula/microbiologia , Arthrobacter/efeitos dos fármacos , Arthrobacter/fisiologia , Sinorhizobium/fisiologia , Sinorhizobium/efeitos dos fármacos , Nodulação/efeitos dos fármacos , Simbiose , Fixação de Nitrogênio/efeitos dos fármacosRESUMO
Resumen La orquídea Guarianthe skinneri está incluida en la norma NOM-059-ECOL-2010 de México como una especie amenazada. Con el fin de estudiar las BPCV (bacterias promotoras del crecimiento vegetal) en esta orquídea, se recolectaron 10 raíces de diferentes plantas para aislar bacterias asociadas a las raíces, que se analizaron mediante pruebas in vitro como: producción de AIA, fijación de nitrógeno, interacción con el hongo micorrízico Thanatephorus sp. cepa RG26 y solubilización de fosfato. De los 71 aislados bacterianos se caracterizaron 10 cepas mediante secuenciación con el marcador 16s rADN y se identificaron seis cepas: Sphingomonas sp., Sinorhizobium sp., Bacillus sp., Nocardia cerradoensis, Bacillus megaterium y Burkholderia phytofirmans. Se observó que la bacteria Sinorhizobium sp. produjo mayor cantidad de AIA (69.189 µg/ml) y Bacillus sp. presentó mayor reducción de acetileno (10.251 nmol cultivo/96 h). En las interacciones de las bacterias y el hongo RG26 se presentaron cuatro categorías (sumamente positivo, positivo, antagonismo 50-50 e inhibición). En relación a la solubilización de fosfato, la bacteria Burkholderia phytofirmans presentó mayor IS a las 48 y 96 hr con IS de 3.11 y 3.48, respectivamente. Los resultados indican que Bacillus sp. pudiera tener las mejores características para promover el desarrollo de la orquídea G. skinneri mediante la inoculación de semillas y plántulas.
Abstract The Guarianthe skinneri orchid is included in NOM-059-ECOL-2010, Mexico standard as an endangered species. In order to study PGPR (promoting growth plant rhizobacteria) from this orchid, 10 roots were collected from different plants to isolate bacteria associated with the roots, which were analyzed by in vitro tests such as: production of AIA, nitrogen fixation, interaction with the mycorrhizal fungus Thanatephorus sp. strain RG26 and phosphate solubilization. We obtain 71 bacterial isolates, 10 strains of them were characterized by sequencing with the 16d rDNA marker identifying six bacteria: Sphingomonas sp. Sinorhizobium sp. Bacillus sp. Nocardia cerradoensis, Bacillus megaterium and Burkholderia phytofirmans. We observed that the bacterium Sinorhizobium sp. produced a greater amount of AIA (69.189 μg/ml) and Bacillus sp. performed greater acetylene reduction (10.251 nmol cultivo/96h). In the interactions of the bacteria and the fungus RG26, four categories were presented (extremely positive, positive, antagonism 50-50 and inhibition). In relation to the solubilization of phosphate, Burkholderia phytofirmans presented higher IS after 48 and 96 hr with an IS of 3.11 and 3.48, respectively. The results indicate that Bacillus sp. it could have the best characteristics to promote the development of the G. skinneri orchid by inoculating seeds and seedlings. Rev. Biol. Trop. 66(3): 953-968. Epub 2018 September 01.
Assuntos
Sinorhizobium , Sphingomonas/crescimento & desenvolvimento , Orchidaceae , Inoculantes Agrícolas , Fungos , MéxicoRESUMO
Native rhizobia are ideal for use as commercial legume inoculants. The characteristics of the carrier used to store the inoculants are important for the survival and symbiotic potential of the rhizobia. The objective of this study was to investigate the effects of peat (PEAT), perlite sugarcane bagasse (PSB), carboxymethyl cellulose plus starch (CMCS), and yeast extract mannitol supplemented with mannitol (YEMM) on the survival, nodulation potential and N2 fixation capacity of the native strains Sinorhizobium mexicanum ITTG R7(T) and Rhizobium calliandrae LBP2-1(T) and of the reference strain Rhizobium etli CFN42(T). A factorial design (4 × 3) with four repetitions was used to determine the symbiotic potential of the rhizobial strains. The survival of the strains was higher for PEAT (46% for strain LBP2-1(T), 167% for strain CFN42(T) and 219% for strain ITTG R7(T)) than for the other carriers after 240 days, except for CFN42(T) kept on CMCS (225%). All the strains kept on the different carriers effectively nodulated common bean, with the lowest number of nodules found (5 nodules) when CFN42(T) was kept on CMCS and with the highest number of nodules found (28 nodules) when ITTG R7(T) was kept on PSB. The nitrogenase activity was the highest for ITTG R7(T) kept on PEAT (4911 µmol C2H4 per fresh weight nodule h(-1)); however, no activity was found when the strains were kept on YEMM. Thus, the survival and symbiotic potential of the rhizobia depended on the carrier used to store them.
Assuntos
Fertilizantes/microbiologia , Phaseolus/crescimento & desenvolvimento , Phaseolus/microbiologia , Rhizobium/metabolismo , Sinorhizobium/metabolismo , Simbiose/fisiologia , Óxido de Alumínio/química , Carboximetilcelulose Sódica/química , Celulose/química , Manitol/química , Fixação de Nitrogênio/fisiologia , Nodulação/fisiologia , Rizosfera , Dióxido de Silício/química , Solo/química , Microbiologia do Solo , Amido/análogos & derivados , Amido/química , Leveduras/químicaRESUMO
Native rhizobia are ideal for use as commercial legume inoculants. The characteristics of the carrier used to store the inoculants are important for the survival and symbiotic potential of the rhizobia. The objective of this study was to investigate the effects of peat (PEAT), perlite sugarcane bagasse (PSB), carboxymethyl cellulose plus starch (CMCS), and yeast extract mannitol supplemented with mannitol (YEMM) on the survival, nodulation potential and N2 fixation capacity of the native strains
Assuntos
Fertilizantes/microbiologia , Phaseolus/crescimento & desenvolvimento , Phaseolus/microbiologia , Rhizobium/metabolismo , Sinorhizobium/metabolismo , Simbiose/fisiologia , Óxido de Alumínio/química , Carboximetilcelulose Sódica/química , Celulose/química , Manitol/química , Fixação de Nitrogênio/fisiologia , Nodulação/fisiologia , Rizosfera , Microbiologia do Solo , Dióxido de Silício/química , Solo/química , Amido/análogos & derivados , Amido/química , Leveduras/químicaRESUMO
Native rhizobia are ideal for use as commercial legume inoculants. The characteristics of the carrier used to store the inoculants are important for the survival and symbiotic potential of the rhizobia. The objective of this study was to investigate the effects of peat (PEAT), perlite sugarcane bagasse (PSB), carboxymethyl cellulose plus starch (CMCS), and yeast extract mannitol supplemented with mannitol (YEMM) on the survival, nodulation potential and N2 fixation capacity of the native strains
Assuntos
Fertilizantes/microbiologia , Phaseolus/crescimento & desenvolvimento , Phaseolus/microbiologia , Rhizobium/metabolismo , Sinorhizobium/metabolismo , Simbiose/fisiologia , Óxido de Alumínio/química , Carboximetilcelulose Sódica/química , Celulose/química , Manitol/química , Fixação de Nitrogênio/fisiologia , Rizosfera , Dióxido de Silício/química , Solo/química , Microbiologia do Solo , Amido/análogos & derivados , Amido/química , Leveduras/químicaRESUMO
Rhizobial bacteria are commonly found in soil but also establish symbiotic relationships with legumes, inhabiting the root nodules, where they fix nitrogen. Endophytic rhizobia have also been reported in the roots and stems of legumes and other plants. We isolated several rhizobial strains from the nodules of noninoculated bean plants and looked for their provenance in the interiors of the seeds. Nine isolates were obtained, covering most known bean symbiont species, which belong to the Rhizobium and Sinorhizobium groups. The strains showed several large plasmids, except for a Sinorhizobium americanum isolate. Two strains, one Rhizobium phaseoli and one S. americanum strain, were thoroughly characterized. Optimal symbiotic performance was observed for both of these strains. The S. americanum strain showed biotin prototrophy when subcultured, as well as high pyruvate dehydrogenase (PDH) activity, both of which are key factors in maintaining optimal growth. The R. phaseoli strain was a biotin auxotroph, did not grow when subcultured, accumulated a large amount of poly-ß-hydroxybutyrate, and exhibited low PDH activity. The physiology and genomes of these strains showed features that may have resulted from their lifestyle inside the seeds: stress sensitivity, a ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) complex, a homocitrate synthase (usually present only in free-living diazotrophs), a hydrogenase uptake cluster, and the presence of prophages. We propose that colonization by rhizobia and their presence in Phaseolus seeds may be part of a persistence mechanism that helps to retain and disperse rhizobial strains.
Assuntos
Fixação de Nitrogênio , Phaseolus/microbiologia , Rhizobium/classificação , Rhizobium/metabolismo , Sinorhizobium/classificação , Sinorhizobium/metabolismo , Simbiose , Dados de Sequência Molecular , Oxirredutases/genética , Rhizobium/isolamento & purificação , Rhizobium/fisiologia , Análise de Sequência de DNA , Sinorhizobium/genética , Sinorhizobium/isolamento & purificaçãoRESUMO
Plasmids have played a major role in bacterial evolution, mainly by their capacity to perform horizontal gene transfer (HGT). Their conjugative transfer (CT) properties are usually described in terms of the plasmid itself. In this work, we analyzed structural and functional aspects of the CT of pLPU83a, an accessory replicon from Rhizobium sp. LPU83, able to transfer from its parental strain, from Ensifer meliloti, or from Rhizobium etli. pLPU83a contains a complete set of transfer genes, featuring a particular organization, shared with only two other rhizobial plasmids. These plasmids contain a TraR quorum-sensing (QS) transcriptional regulator, but lack an acyl-homoserine lactone (AHL) synthase gene. We also determined that the ability of pLPU83a to transfer from R. etli CFN42 genomic background was mainly achieved through mobilization, employing the machinery of the endogenous plasmid pRetCFN42a, falling under control of the QS regulators from pRetCFN42a. In contrast, from its native or from the E. meliloti background, pLPU83a utilized its own machinery for conjugation, requiring the plasmid-encoded traR. Activation of TraR seemed to be AHL independent. The results obtained indicate that the CT phenotype of a plasmid is dictated not only by the genes it carries, but by their interaction with its genomic context.
Assuntos
Conjugação Genética , Transferência Genética Horizontal , Plasmídeos/genética , Rhizobium/genética , Proteínas de Bactérias/genética , Genoma Bacteriano , Filogenia , Plasmídeos/classificação , Sinorhizobium/genética , Fatores de Transcrição/genéticaRESUMO
In bacteria, niche adaptation may be determined by mobile extrachromosomal elements. A remarkable characteristic of Rhizobium and Ensifer (Sinorhizobium) but also of Agrobacterium species is that almost half of the genome is contained in several large extrachromosomal replicons (ERs). They encode a plethora of functions, some of them required for bacterial survival, niche adaptation, plasmid transfer or stability. In spite of this, plasmid loss is common in rhizobia upon subculturing. Rhizobial gene-expression studies in plant rhizospheres with novel results from transcriptomic analysis of Rhizobium phaseoli in maize and Phaseolus vulgaris roots highlight the role of ERs in natural niches and allowed the identification of common extrachromosomal genes expressed in association with plant rootlets and the replicons involved.
Assuntos
Raízes de Plantas/genética , Plasmídeos , Rhizobium , Agrobacterium/genética , Agrobacterium/metabolismo , Herança Extracromossômica , Regulação Bacteriana da Expressão Gênica , Dados de Sequência Molecular , Phaseolus/microbiologia , Plasmídeos/genética , Plasmídeos/metabolismo , RNA Ribossômico 16S , Replicon , Rhizobium/genética , Rhizobium/metabolismo , Rizosfera , Análise de Sequência de DNA , Sinorhizobium/genética , Sinorhizobium/metabolismo , Zea mays/microbiologiaRESUMO
Rhizobia are Gram-negative bacteria that live in soils and associate with leguminous plants to establish nitrogen-fixing symbioses. The ability of these bacteria to undergo horizontal gene transfer (HGT) is thought to be one of the main features to explain both the origin of their symbiotic life-style and the plasticity and dynamics of their genomes. In our laboratory we have previously characterized at the species level the non-pSym plasmid mobilome in Sinorhizobium meliloti, the symbiont of Medicago spp., and have found a high incidence of conjugal activity in many plasmids (Pistorio et al., 2008). In this work we characterized the Dtr (DNA-transfer-and-replication) region of one of those plasmids, pSmeLPU88b. This mobilization region was found to represent a previously unclassified Dtr type in rhizobia (hereafter type-IV), highly ubiquitous in S. meliloti and found in other genera of Gram-negative bacteria as well; including Agrobacterium, Ochrobactrum, and Chelativorans. The oriT of the type-IV Dtr described here could be located by function within a DNA fragment of 278 bp, between the divergent genes parA and mobC. The phylogenetic analysis of the cognate relaxase MobZ indicated that this protein groups close to the previously defined MOB(P3) and MOB(P4) type of enzymes, but is located in a separate and novel cluster that we have designated MOB(P0). Noteworthy, MOB(P0) and MOB(P4) relaxases were frequently associated with plasmids present in rhizospheric soil bacteria. A comparison of the nod-gene locations with the phylogenetic topology of the rhizobial relaxases revealed that the symbiotic genes are found on diverse plasmids bearing any of the four Dtr types, thus indicating that pSym plasmids are not specifically associated with any particular mobilization system. Finally, we demonstrated that the type-IV Dtr promoted the mobilization of plasmids from S. meliloti to Sinorhizobium medicae as well as from these rhizobia to other bacteria by means of their own helper functions. The results present an as-yet-unclassified and seemingly ubiquitous conjugal system that provides a mechanistic support for the HGT between sympatric rhizobia of Medicago roots, and between other soil and rhizospheric bacteria.
Assuntos
DNA Bacteriano/isolamento & purificação , Genes Bacterianos , Bactérias Gram-Negativas/genética , Sinorhizobium meliloti/genética , Sinorhizobium/genética , Microbiologia do Solo , Sequência de Bases , Conjugação Genética , DNA Bacteriano/genética , Transferência Genética Horizontal , Bactérias Gram-Negativas/classificação , Medicago/microbiologia , Dados de Sequência Molecular , Fixação de Nitrogênio , Filogenia , Raízes de Plantas/microbiologia , Plasmídeos , Sinorhizobium/classificação , Sinorhizobium meliloti/classificação , Simbiose/genética , SimpatriaRESUMO
Alfalfa (Medicago sativa) is the most cultivated forage legume for cattle and animal feeding, occupying about 32 million hectares over the world. Management of the N2-fixing symbiosis of this plant to maximize crop production is therefore an important objective. A fundamental constraint to this aim emerges when a moderately low soil pH hampers the establishment of an effective symbiosis with indigenous and/or inoculated rhizobia. Besides the association of alfalfa with Ensifer (Sinorhizobium) meliloti, this legume is able to establish a symbiosis with Ensifer (Sinorhizobium) medicae and with less characterized types of rhizobia, such as the Oregon-like strains, Rhizobium sp. Or191 initially isolated in the USA, and the Rhizobium sp. LPU83 strain, from Argentina. These strains are acid-tolerant, highly competitive for acidic-soil-alfalfa nodulation, but inefficient for biological nitrogen fixation with alfalfa. These features position the Oregon-like rhizobia as strains of potential risk in agricultural soils compared with the efficient symbiont E. meliloti. Moreover, the collected genetic information has revealed that the genomic structure of these rhizobial isolates is complex in terms of sequence similarities shared with other rhizobia. Such a "patched" genetic composition has obviously imposed severe restrictions to the classical taxonomy of these rhizobia. In this work we summarize the accumulated knowledge about the Oregon-like rhizobia and present a phylogenetic analysis based on genome sequence data of Rhizobium sp. LPU83 obtained by a high-throughput sequencing on the Genome Sequencer FLX Titanium platform. The accessibility of the complete genomic sequence will release up more experimental possibilities since this information will then enable biochemical studies as well as proteomics and transcriptomics approaches.
Assuntos
Genoma Bacteriano , Genômica/métodos , Rhizobium/genética , Variação Genética , Medicago sativa/microbiologia , Fixação de Nitrogênio/genética , Filogenia , Plasmídeos/genética , Rhizobium/classificação , Rhizobium/metabolismo , Sinorhizobium/genética , Simbiose/genéticaRESUMO
Bacteria from nodules of the legume Acaciella angustissima native to the south of Mexico were characterized genetically and their nodulation and competitiveness were evaluated. Phylogenetic studies derived from rpoB gene sequences indicated that A. angustissima is nodulated by Sinorhizobium mexicanum, Rhizobium tropici, Mesorhizobium plurifarium and Agrobacterium tumefaciens and by bacteria related to Sinorhizobium americanum, Sinorhizobium terangae, Rhizobium etli and Rhizobium gallicum. A new lineage related to S. terangae is recognized based on the sequences of gyrA, nolR, recA, rpoB and rrs genes, DNA-DNA hybridization and phenotypic characteristics. The name for this new species is Sinorhizobium chiapanecum and its type strain is ITTG S70T. The symbiotic genes nodA and nifH were similar to those from S. mexicanum strains, which are Acaciella symbionts as well, with nodA gene sequences grouped within a cluster of nod genes from strains that nodulate plants from the Mimosoideae subfamily of the Leguminosae. Sinorhizobium isolates were the most frequently obtained from A. angustissima nodules and were among the best strains to promote plant growth in A. angustissima and to compete in interstrain nodule competition assays. Lateral transfer of symbiotic genes is not evident among the genera that nodulate A. angustissima (Rhizobium, Sinorhizobium and Mesorhizobium) but may occur among the sympatric and closely related sinorhizobia that nodulate Acaciella.
Assuntos
Fabaceae/microbiologia , Fixação de Nitrogênio , Rhizobium , Simbiose , Técnicas de Tipagem Bacteriana , Fabaceae/crescimento & desenvolvimento , México , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Filogenia , Rhizobium/classificação , Rhizobium/genética , Rhizobium/fisiologia , Análise de Sequência de DNA , Sinorhizobium/classificação , Sinorhizobium/genética , Sinorhizobium/fisiologia , Especificidade da Espécie , Simbiose/genéticaRESUMO
The comparative analysis of genomic characteristics and single-nucleotide polymorphism patterns from large fragments borne on different replicons of Sinorhizobium spp. genomes clearly demonstrate that DNA recombination among closely related bacteria is a major event in the diversification of this genome, especially in pSymA, resulting in mosaic structure.
Assuntos
Variação Genética , Genoma Bacteriano , Polimorfismo Genético , Sinorhizobium/genética , DNA Bacteriano/química , DNA Bacteriano/genética , Evolução Molecular , Dados de Sequência Molecular , Recombinação Genética , Análise de Sequência de DNARESUMO
We studied the genetic structure of 176 bacterial isolates from nodules of Medicago sativa, M. lupulina and M. polymorpha in fifteen sites distributed in three localities in Mexico. The strains were characterized by multilocus enzyme electrophoresis, plasmid profiles, PCR restriction fragment length polymorphism of 16S rRNA genes and of the intergenic spacer between 16S and 23S rRNA genes, and partial sequences of glnII, recA and nodB. Most of the strains were classified as Sinorhizobium meliloti, and a high genetic diversity was recorded. Six strains were classified as Sinorhizobium medicae, with no genetic variation. Phylogenetic and population genetic analyses revealed evidence of frequent recombination and migration within species.
Assuntos
Medicago sativa/microbiologia , Sinorhizobium meliloti/genética , Sinorhizobium/genética , Microbiologia do Solo , Proteínas de Bactérias/genética , DNA Bacteriano/genética , DNA Ribossômico/genética , DNA Espaçador Ribossômico/genética , Enzimas/genética , Evolução Molecular , Variação Genética , Desequilíbrio de Ligação , México , Filogenia , Plasmídeos/genética , RNA Ribossômico 16S/genética , Nódulos Radiculares de Plantas/microbiologiaRESUMO
A new lineage of Ensifer nodulating the American legume Acacia angustissima in the tropical forest of Chiapas and Morelos, Mexico is described. Bacteria were identified as Ensifer with ssb or nolR specific primers. Phylogenetic analysis with partial sequences of the five chromosomal genes gyrA, nolR, recA, rpoB and rrs revealed that this new lineage is related to African Ensifer terangae. The results of total DNA-DNA hybridization and selected phenotypic tests among the A. angustissima strains and E. terangae indicated that they belong to different species. The phylogeny with the symbiotic nifH gene also separates this group as a different clade but with close affinities to bacteria belonging to the genus Ensifer isolated from American hosts. ITTG R7(T) (=CFN ER1001, HAMBI 2910, CIP 109033, ATCC BAA-1312, DSM18446) is the type strain of a new species for which the name Ensifer mexicanus sp. nov. is proposed.
Assuntos
Acacia/microbiologia , Alphaproteobacteria/classificação , Alphaproteobacteria/genética , Alphaproteobacteria/isolamento & purificação , Proteínas de Bactérias/genética , Cromossomos Bacterianos/genética , Genes Bacterianos/genética , México , Fixação de Nitrogênio/genética , Hibridização de Ácido Nucleico , Filogenia , Homologia de Sequência , Sinorhizobium/classificação , Especificidade da Espécie , SimbioseRESUMO
The lipopolysaccharides (LPS) are major components of the outer membrane of Gram negative bacteria and, because of their location, are important mediators in the interaction between these bacteria and their environment and other organisms. The alpha-Proteobacterial family Rhizobiaceae includes the rhizobia and agrobacteria, microorganisms which establish symbiotic or parasitic relationships with plants. Mutants deficient in LPS biosynthesis show anomalous interactions with their hosts. The agronomical relevance of the relationship between rhizobia and agrobacteria with plants has promoted a large number of studies on the LPS from these bacteria. The complete structures of one or several domains of LPS from Rhizobiaceae have been determined in the last years. Additionally, several metabolic steps in the biosynthesis of these molecules have been elucidated. This review aims at the description of the more recent findings on the structure and biosynthesis of LPS in Rhizobium, Sinorhizobium and Agrobacterium.
Assuntos
Lipopolissacarídeos/química , Rhizobiaceae/química , Sequência de Carboidratos , Lipídeo A/biossíntese , Lipídeo A/química , Lipopolissacarídeos/biossíntese , Dados de Sequência Molecular , Estrutura Molecular , Antígenos O/química , Rhizobiaceae/genética , Rhizobiaceae/metabolismo , Rhizobium/química , Rhizobium/genética , Rhizobium/metabolismo , Nódulos Radiculares de Plantas/microbiologia , Sinorhizobium/química , Sinorhizobium/genética , Sinorhizobium/metabolismo , Especificidade da EspécieRESUMO
Sinorhizobium arboris and S. kostiense are rhizobia that nodulate the tropical leguminous trees Acacia senegal and Prosopis chilensis. The lipochito-oligosaccharidic signalling molecules (LCOs) of S. arboris HAMBI 2361 and S. kostiense HAMBI 2362 were analyzed by mass spectrometry. The major LCOs produced by the strains were shown to be pentameric, acylated with common fatty acids, N-methylated, O-6-carbamoylated and partially sulfated, as are the LCOs characterized to date for other Acacia-nodulating rhizobia. Besides the major LCOs the two strains produced (i) tetrameric LCOs, (ii) LCOs acylated with fatty acids other than those commonly found, (iii) LCOs with only an acyl substituent and (iv) noncarbamoylated LCOs. Production of LCOs (i) to (iii) are novel among Acacia-nodulating rhizobia. The roles of the different structural characteristics of LCOs in the rhizobium-A. senegal symbiosis are discussed. Specific structural features of the LCOs are proposed to be important in the selection of effective nitrogen-fixing rhizobia by A. senegal.
Assuntos
Acacia/metabolismo , Prosopis/metabolismo , Sinorhizobium/metabolismo , Enxofre/química , Sequência de Carboidratos , Cromatografia Líquida , Ligação Genética , Íons , Espectrometria de Massas , Metilação , Modelos Químicos , Monossacarídeos/química , Oligossacarídeos/química , Plasmídeos/metabolismo , Rhizobium/metabolismo , Espectrometria de Massas por Ionização por ElectrosprayRESUMO
The genome of the nitrogen-fixing bacterium Sinorhizobium meliloti is composed of three replicons of 3.65 (chromosome), 1.35 (pSymA) and 1.68 Mb (pSymB), respectively. While the chromosome encodes for most of the housekeeping functions, the three elements may contribute to symbiosis, though pSymA is absolutely necessary for nodulation and nitrogen fixation, since it harbours all the characterized nodulation and symbiotic fixation genes. On the other hand, the majority of the sequences located in this megaplasmid are probably not expressed during the free-living stage of the organism. Since most of the sequences located in pSymA are transcribed only at the stage of bacteroids when most probably the fate of the bacterium is to die, the mutations occurring at this stage will not be fixed in the population. Therefore, if natural selection contributes to the codon usage pattern in this species, its effect will be much weaker for the genes placed in pSymA. A codon usage analysis of the genes comprising the three replicons is consistent with the conclusion that selection for translational speed shapes the codon usage of the two replicons which are important for competitive cell growth while the codon usage of the third replicon reflects primarily the mutational bias.
Assuntos
Códon/genética , Biossíntese de Proteínas/genética , Replicon/genética , Seleção Genética , Sinorhizobium meliloti/genética , Sequência de Bases , Biologia Computacional/métodos , Genes Bacterianos/genética , Genoma Bacteriano , Sinorhizobium/genética , Especificidade da EspécieRESUMO
In this paper the influence of the exopolysaccharides produced by Sinorhizobium meliloti strains on the nodulation rates in alfalfa plants has been considered. The experiments were performed in a rotary shaker and in an air-lift type fermentor. Different Sinorhizobium meliloti strains were used. Bacterial growth rates were determined by viable cell counts. Exopolysaccharide concentration was determined by precipitation with ethanol. It was observed that maximum cell concentration was in the order of 1 x 10(10) cell/ml and exopolysaccharide content was approximately 11 g/l. The experiments performed with alfalfa plants in a controlled environment chamber showed that, when inoculation was carried out with diluted suspensions (1/10), nodulation time was reduced from 10 to 4 days, while the strains retained their symbiotic properties.
Assuntos
Técnicas Bacteriológicas/instrumentação , Medicago sativa/microbiologia , Polissacarídeos Bacterianos/biossíntese , Sinorhizobium/crescimento & desenvolvimento , Aerobiose , Meios de Cultura/metabolismo , Fermentação , Oxigênio/farmacologia , Sinorhizobium/efeitos dos fármacos , Sinorhizobium/metabolismo , Fatores de TempoRESUMO
The sinorhizobia isolated from root nodules of Acacia species native of Mexico constitute a diverse group of bacteria on the basis of their metabolic enzyme electromorphs but share restriction patterns of the PCR products of 16S rRNA genes and a common 500 kb symbiotic plasmid. They are distinguished from other Sinorhizobium species by their levels of DNA-DNA hybridization and the sequence of 16S rRNA and nifH genes. nolR gene hybridization patterns were found useful to identify sinorhizobia and characterize species. A new species, Sinorhizobium americanus, is described and the type strain is CFNEI 156 from Acacia acatlensis.
Assuntos
Acacia/microbiologia , Fixação de Nitrogênio , Sinorhizobium/classificação , Acacia/classificação , Sequência de Bases , Farmacorresistência Bacteriana Múltipla , Enzimas/análise , Enzimas/classificação , Enzimas/metabolismo , Canamicina/farmacologia , México , Ácido Nalidíxico/farmacologia , Hibridização de Ácido Nucleico , Filogenia , Raízes de Plantas/microbiologia , RNA Ribossômico 16S/genética , Sinorhizobium/genética , Sinorhizobium/isolamento & purificação , Sinorhizobium/ultraestrutura , Microbiologia do SoloRESUMO
Sinorhizobium morelense sp. nov. is described to designate a group of bacteria isolated from root nodules of Leucaena leucocephala. S. morelense shows 98% 16S rRNA gene sequence similarity to some Sinorhizobium species and to Ensifer adhaerens. This novel species is distinguished from other Sinorhizobium species and from E. adhaerens by DNA-DNA hybridization, 165 rRNA gene restriction fragments and sequence and some distinctive phenotypic features. Strains of this species are highly resistant to some antibiotics, such as carbenicillin (1 mg ml(-1)), kanamycin (500 microg ml(-1)) and erythromycin (300 microg ml(-1)). They do not form nodules, but a nodulating strain, Lc57, is closely related to the novel species. Strain Lc04T (= LMG 21331T = CFN E1007T) is designated as the type strain of this novel species.