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1.
Syst Appl Microbiol ; 35(3): 156-64, 2012 May.
Artigo em Inglês | MEDLINE | ID: mdl-22429391

RESUMO

Salinity is an increasing problem in Africa affecting rhizobia-legume symbioses. In Morocco, Phaseolus vulgaris is cultivated in saline soils and its symbiosis with rhizobia depends on the presence of osmotolerant strains in these soils. In this study, 32 osmotolerant rhizobial strains nodulating P. vulgaris were identified at the species and symbiovar levels by analysing core and symbiotic genes, respectively. The most abundant strains were closely related to Rhizobium etli and R. phaseoli and belonged to symbiovar phaseoli. A second group of strains was identified as R. gallicum sv gallicum. The remaining strains, identified as R. tropici, belonged to the CIAT 899(T) nodC group, which has not yet been described as a symbiovar. In representative strains, the otsA gene involved in the accumulation of trehalose and putatively in osmotolerance was analysed. The results showed that the phylogeny of this gene was not completely congruent with those of other core genes, since the genus Ensifer was more closely related to some Rhizobium species than others. Although the role of the otsA gene in osmotolerance is not well established, it can be a useful protein-coding gene for phylogenetic studies in the genus Rhizobium, since the phylogenies of otsA and other core genes are coincident at the species level.


Assuntos
Biodiversidade , Glucosiltransferases/genética , Phaseolus/microbiologia , Nodulação , Rhizobium/classificação , Rhizobium/isolamento & purificação , Microbiologia do Solo , Análise por Conglomerados , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Genótipo , Dados de Sequência Molecular , Tipagem Molecular , Marrocos , Pressão Osmótica , Filogenia , Raízes de Plantas/microbiologia , RNA Ribossômico 16S/genética , Técnica de Amplificação ao Acaso de DNA Polimórfico , Rhizobium/enzimologia , Rhizobium/genética , Análise de Sequência de DNA , Trealose/metabolismo
2.
Proc Natl Acad Sci U S A ; 105(19): 7064-9, 2008 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-18458328

RESUMO

The rhizobia-legume, root-nodule symbiosis provides the most efficient source of biologically fixed ammonia fertilizer for agricultural crops. Its development involves pathways of specificity, infectivity, and effectivity resulting from expressed traits of the bacterium and host plant. A key event of the infection process required for development of this root-nodule symbiosis is a highly localized, complete erosion of the plant cell wall through which the bacterial symbiont penetrates to establish a nitrogen-fixing, intracellular endosymbiotic state within the host. This process of wall degradation must be delicately balanced to avoid lysis and destruction of the host cell. Here, we describe the purification, biochemical characterization, molecular genetic analysis, biological activity, and symbiotic function of a cell-bound bacterial cellulase (CelC2) enzyme from Rhizobium leguminosarum bv. trifolii, the clover-nodulating endosymbiont. The purified enzyme can erode the noncrystalline tip of the white clover host root hair wall, making a localized hole of sufficient size to allow wild-type microsymbiont penetration. This CelC2 enzyme is not active on root hairs of the nonhost legume alfalfa. Microscopy analysis of the symbiotic phenotypes of the ANU843 wild type and CelC2 knockout mutant derivative revealed that this enzyme fulfils an essential role in the primary infection process required for development of the canonical nitrogen-fixing R. leguminosarum bv. trifolii-white clover symbiosis.


Assuntos
Celulase/metabolismo , Fabaceae/microbiologia , Raízes de Plantas/microbiologia , Rhizobium leguminosarum/enzimologia , Simbiose , Celulase/genética , Celulase/isolamento & purificação , Celulose/biossíntese , Clonagem Molecular , Fabaceae/citologia , Genes Bacterianos , Ligação Genética , Medicago/citologia , Medicago/microbiologia , Dados de Sequência Molecular , Mutação/genética , Fenótipo , Raízes de Plantas/citologia , Rhizobium leguminosarum/citologia , Rhizobium leguminosarum/genética , Nódulos Radiculares de Plantas/citologia , Nódulos Radiculares de Plantas/microbiologia , Plântula/microbiologia
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