RESUMO
The structure of the extracellular polysaccharide (EPS) produced by the Rhizobium sp. B strain isolated from atypical nodules on alfalfa has been determined using a combination of chemical and physical techniques (methylation analysis, high pH-anion exchange chromatography (HPAEC), mass spectrometry and 1-D and 2-D NMR spectroscopy). As opposed to the EPS from other strains of Rhizobium, the EPS from the sp. B strain contains D-Glc together with L-Rha and 2-deoxy-D-arabino-hexuronic acid. It is a polymer of a repeating unit having the following structure: --> 4)-beta-D-Glcp-(1 --> 4)-alpha-L-Rhap -(1 --> 3)-beta-D-Glcp-(1 --> 4)-2-deoxy-beta-D-GlcpA-(1 -->. The polysaccharide also contains 0.6 O-acetyl groups per sugar which have not been located.
Assuntos
Polissacarídeos Bacterianos/química , Polissacarídeos Bacterianos/isolamento & purificação , Rhizobium/química , Acetilação , Configuração de Carboidratos , Sequência de Carboidratos , Cromatografia por Troca Iônica , Cromatografia Gasosa-Espectrometria de Massas , Glucose/análise , Medicago sativa/microbiologia , Dados de Sequência Molecular , Ressonância Magnética Nuclear Biomolecular , Ramnose/análise , Rhizobium/isolamento & purificaçãoRESUMO
The Rhizobium sp. T1 strain. which induces nodule formation on alfalfa and clover roots, produces, during growth, an extracellular polysaccharide composed of D-glucose and D-glucuronic acid noted glucoglucuronan. During the bacterial growth, the pH of the medium decreases slightly. The control of pH in the growth medium slightly reduces the glucoglucuronan production. Under the conditions tested in the present work, the weight-average molecular weight of the polymers produced with or without pH control are similar: Mw approximately 2 x 10(6); the repeating unit determined by chemical and NMR analyses corresponds to the disaccharide: --> 3)-beta-D-GlcpA-(1-->4)-beta-D-Glcp-(1 -->.
