Abstract
Rhizobium tropici is a Gram-negative bacterium that induces nodules and fixed atmospheric nitrogen in symbiotic association with Phaseolus vulgaris (common bean) and some other leguminous species. Lectins are proteins that specifically bind to carbohydrates and, consequently, modulate different biological functions. In this study, the d-glucose/d-mannose-binding lectins (from seeds of Dioclea megacarpa, D. rostrata and D. violacea) and d-galactose-binding lectins (from seeds of Bauhinia variegata, Erythina velutina and Vatairea macrocarpa) were purified using chromatographic techniques and evaluated for their effect on the growth of R. tropici CIAT899. All lectins were assayed with a satisfactory degree of purity according to SDS-PAGE analysis, and stimulated bacterial growth; in particular, the Dioclea rostrata lectin was the most active among all tested proteins. As confirmed in the present study, both d-galactose- and d-glucose/d-mannose-binding lectins purified from the seeds of leguminous plants may be powerful biotechnological tools to stimulate the growth of R. tropici CIAT99, thus improving symbiotic interaction between rhizobia and common bean and, hence, the production of this field crop.
Highlights
IntroductionIn 1991, Martinez-Romero and colleagues [2] identified a new species of common bean symbionts: Rhizobium tropici
Rhizobia are soil bacteria best known as root-nodule symbionts of legumes [1]
A different pattern was seen for B. variegata lectin (BVL) and
Summary
In 1991, Martinez-Romero and colleagues [2] identified a new species of common bean symbionts: Rhizobium tropici. This new rhizobial species was described as aerobic, Gram-negative, with optimal pH for growth ranging between 5 and 7, and characterized by high genetic stability of the symbiotic plasmid and tolerance to tropical environmental stresses such as high temperature and low soil pH [2]. CIAT899, known commercially as SEMIA 4077, the type-strain of R. tropici, was isolated at the Centro Internacional de Agricultura Tropical (CIAT) in Colombia, and it was recognized as an effective symbiont of the common bean, Leucaena leucocephala and some other leguminous species [2,3]. Based on its superior characteristics as a common bean root-nodule symbiont, this strain is currently recommended (authorized) for the production of commercial rhizobial inoculant for common bean production in Brazil [6]
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