Physiological and symbiotic diversity of Cupriavidus necator strains isolated from nodules of Leguminosae species

Abstract

Biological nitrogen fixation, performed by diazotrophic bacteria, plays an important role in the maintenance of agricultural systems, as it contributes with significant amounts of the nitrogen (N) needed for plant growth, totally or partially exempting the use of industrial N fertilisers. Twenty-five bacterial strains isolated from nodules of Leucaena leucocephala and Phaseolus vulgaris trap plants were studied. These nodules were formed after inoculation with suspensions of soil samples collected close to the root system of Sesbania virgata. In previous studies, these bacteria were identified as Cupriavidus necator. This study aimed to evaluate the ability of these strains to fix N2 in the free-living state and to use carbon (C) sources; their resistance to antibiotics; growth in media with different pH values and salt concentrations and symbiotic efficiency with L. leucocephala and P. vulgaris. In each test, these strains were compared to C. taiwanensis LMG 19424T. Although a high variability regarding antibiotic resistance, salt tolerance and use of C sources were observed among the 25 C. necator strains, a large group behaved similar regarding salt tolerance (20 strains) and antibiotic resistance (22 strains). C. necator strains behaved in a different way of LMG 19424T. Only one of the 25 strains studied, UFLA02-69, was not able to establish symbiosis with its trap species, P. vulgaris. Only the strains LMG19424T and UFLA01-672 were efficient in symbiosis with L. leucocephala. The ability to use C sources, grow in different pHs and salt concentrations and resistance to several antibiotics, may grant high saprophytic competence and greater competitivity to these strains in relation to the native Leguminosae-nodulating bacterial populations, suggesting potential use in inoculant strain selection studies for legumes cultivated in soils with a wide range of pH and salt concentrations.