Caracterización fenotípica y genotípica de doce rizobios aislados de diversas regiones geográficas de Venezuela

Abstract

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.Key words: Rhizobium, Bradyrhizobium, phenotypic characterization, PCR-RFLP, 16S rDNA.Las bacterias denominadas comúnmen-te rizobios presentan varias formas de vida; pueden comportarse como saprófitos en el suelo establecer una asociación simbiótica y formar nódulos con las raíces y tallos de las leguminosas, donde tiene lugar la reducción del nitrógeno atmosférico en amonio, el cual es transportado a la planta y convertido en biomoléculas esenciales, o bien estar presentes como endófito en raíces de diferentes especies vegetales, donde ejercen efectos promotores del crecimiento (Wang et al. 2001).La taxonomía ...

Morphophysiological characterization of rhizobia isolated from wild genotypes of the common bean

“…1999). This indicates that most of isolates obtained in this study, regardless of soil origin, have characteristics similar to those of Rhizobium genus, due mainly to the acidity of the culture medium and displaying fast growth, as well as other features like colonies with a diameter >2 mm and high mucus production (PINTO et al, 2007;MARQUINA et al 2011;DALL'AGNOL et al 2013). Nevertheless, high morphological diversity was observed among the obtained isolates, whereas the isolates showed unusual characteristics for the genus Rhizobium, such as neutral pH, slow growth and small production of mucus (Figure 1).…”

“…All those characteristics are common among bacteria belonging to the genus Rhizobium (PINTO et al, 2007;MARQUINA et al 2011;DALL'AGNOL et al 2013). Among the isolates obtained from soil samples from Goiás, most of those acidified the culture medium, formed colonies >2 mm, showed fast growth, yellow coloring, few quantity of mucus and heterogeneous appearance ( Figure 1A).…”

Aislamiento y caracterización morfológica de bacterias del género Bradyrhizobium provenientes de parcelas agrícolas de la localidad de Loma Plata, Boquerón-Paraguay

“…El análisis de los 4 aislados incluyó primeramente la velocidad de crecimiento que se dio en 6 días, por lo que se clasifica a los aislados como rizobios de crecimiento lento según las categorías establecidas por Marquina et al, 2011 (26) . (27) .…”

Efecto de la inoculación de plantas de Tarwi con cepas de Bradyrhizobium spp. aisladas de un lupino silvestre, en condiciones de invernadero

“…Los aislamientos fueron dirigidos a purificar cepas rizobianas de crecimiento lento (5 a 7 días) y que vira el medio LMA con azul de bromotimol de verde a color azul (Cuadrado et al 2009, Marquina et al 2011 por la producción de álcali en el medio, características propias de los Bradyrhizobium. Se obtuvieron un total de ocho aislados con estas características.…”