Polyphasic characterization of forage legumes root nodule bacteria isolated from semiarid region in Brazil

Abstract

Forage legumes are important resources in semiarid regions due to their abilities to adapt to soils with low fertility and fix nitrogen when associated with diazotrophic bacteria. Here, we applied a polyphasic approach to characterize a set of legume nodule isolates obtained from Clitoria ternatea and Stylosanthes capitata cultivated in the soils of a semiarid region of Brazil. A total of 126 bacterial isolates were obtained: 45 isolates from C. ternatea and 81 isolates from S. capitata. Nodulation tests revealed only ten isolates that nodulated their original host: six isolates from C. ternatea and four isolates from S. capitate. These ten legume nodule isolates were phenotypically and genotypically characterized. All isolates grew in fructose, glucose, sodium glutamate, maltose, xylose, and sucrose. Metabolic tests showed a relationship between tolerance to salt and high temperatures, where isolates that tolerated the highest salt concentration also tolerated the highest temperature. Three isolates showed amylolytic activity, and four isolates showed carboxymethyl cellulolytic activity. Streptomycin was the most limiting and nalidixic acid was the least limiting antibiotic to bacterial growth. Seven out of ten isolates were indol-acetic acid producers. Additionally, 16S rRNA gene partial sequencing enabled the identification of members of the generaBacillus (1), Bradyrhizobium (4), Leifsonia (3), Microvirga (1), and Rhizobium (1). These data reveal phenotypically and genotypically diverse bacteria inhabiting the nodules of the forage legumes C. ternatea and S. capitatarepresent an important microbial source to protect new biotechnological products and improve forage legumes in semiarid regions.