Resumo

MARQUINA, María Eugenia; GONZALEZ, Néstor Enrique  e  CASTRO, Yulimar. Caracterización fenotípica y genotípica de doce rizobios aislados de diversas regiones geográficas de Venezuela. Rev. biol. trop [online]. 2011, vol.59, n.3, pp.1017-1036. ISSN 0034-7744.

Phenotypic and genotypic characterization of twelve rhizobial isolates from different regions of Venezuela. Rhizobial taxonomy and  systematics have progressed substantially, nevertheless, few studies have been developed on venezuelan species. This study evaluated the  phenotypic and genetic variation between 12 venezuelan indigenous rhizobial isolates and 10 international referential strains, by phenotypical traits  and DNA molecular markers. In this regard, a PCR-RFLP of the 16S rDNA gene, the presence of large plasmids, metabolic assays in solid media,  salinity resistance, pH and temperature growth conditions, and intrinsic antibiotic resistance were assayed. In reference to the phenotypic  attributes, we recognized three main groups: A group I, which comprised all the strains metabolizing between 67.5%-90% of the C and N sources.  They were also acid-tolerant, as well as acid producers, capable of growing at 40ºC and in high salinity conditions (2-2.5% NaCl). With regard to the antibiotic sensitivity, this group was susceptible to a 30% of the antibiotic assayed. Strains belonging to Group II exhibited a lower salt  tolerance (0.1-1.5%NaCl), as well as a lower acid tolerance, since they grew well at pH values equal or higher than 5.0. This group appeared to be  resistant to all of the antibiotics assayed and only metabolized between 52.5%-82.5% of the C and N sources. Group III was represented by a  single bacterial strain: it has a extremely low salt tolerance (0.1% NaCl). This strain grew at a pH equal or higher than 5.6, was susceptible to 50%  of the antibiotics assayed and metabolized 72% of the C and N sources. On the basis of a PCR- RFLP of the 16S rDNA, three groups were also  obtained. Members of the group A showed a close resemblance to Rhizobium tropici CIAT 899 and Sinorhizobium americanum CFN-EI 156, while  Group B was closely related to Bradyrhizobium spp. Group C, was also represented by only one isolate. The Trebol isolate, was the only one strain  able to form nodules and does not appear to be related to any of the referential rhizobial strains, suggesting a possible symbiotic horizontal gene  transfer. Finally, in this work, there are evidences of a genetic diversity in the venezuelan rhizobial strains. A different geographical origin is  perhaps an important factor affecting the diversity of the indigenous rhizobia in this study. Rev. Biol. Trop. 59 (3): 1017-1036. Epub 2011 September 01.

Palavras-chave : Rhizobium; Bradyrhizobium; phenotypic characterization; PCR-RFLP; 16S rDNA.

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