Rhizobium freirei sp. nov., a symbiont of Phaseolus vulgaris that is very effective at fixing nitrogen

Abstract

Common bean (Phaseolus vulgaris L.) can establish symbiotic associations with several Rhizobium species; however, the effectiveness of most strains at fixing nitrogen under field conditions is very low. PRF 81 T is a very effective strain, usually referred to as Rhizobium tropici and used successfully in thousands of doses of commercial inoculants for the common bean crop in Brazil; it has shown high rates of nitrogen fixation in all areas representative of the crop in the country. Here, we present results that indicate that PRF 81 T , although it belongs to the 'R. tropici group', which includes 10 Rhizobium species, R. tropici, R. leucaenae, R. lusitanum, R. multihospitium, R. miluonense, R. hainanense, R. calliandrae, R. mayense, R. jaguaris and R. rhizogenes, represents a novel species. Several morpho-physiological traits differentiated PRF 81 T from related species. Differences were also confirmed in the analysis of rep-PCR (sharing less than 45 % similarity with the other species), MLSA with recA, atpD and rpoB genes, and DNA-DNA hybridization. The novel species, for which we propose the name Rhizobium freirei sp. nov., is able to establish effective root nodule symbioses with Phaseolus vulgaris, Leucaena leucocephala, Leucaena esculenta, Crotalaria juncea and Macroptilium atropurpureum. The type strain is PRF 81 T (5CNPSo 122 T 5SEMIA 4080 T 5IPR-Pv81 T 5WDCM 440 T ).

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).…”

“…The strains of the species R. tropici and R. freirei have a great ability to use carbon sources, the latter of which has relatively lower capacity (DALL'AGNOL et al 2013). The results presented in our study corroborate these authors and indicate that many of the tested isolates have characteristics very similar to those showed by the standard strains of R. tropici (SEMIA 4077 and SEMIA 4088) and R. freirei (SEMIA 4080) used in Brazil as commercial inoculant for common bean.…”

Rhizobium paranaense sp. nov., an effective N2-fixing symbiont of common bean (Phaseolus vulgaris L.) with broad geographical distribution in Brazil

“…Alignments and phylogenies were obtained with MEGA 5.1 software, using the maximum-likelihood (Felsenstein, 1981) algorithm, as suggested by Tindall et al (2010), as well as the neighbour-joining (Saitou & Nei, 1987) algorithm and Kimura two-parameter (K2P) distances (Kimura, 1980). The 16S rRNA gene phylogeny based on the maximum-likelihood algorithm showed that strains PRF 35 T , PRF 54, CPAO 1135 and H 52 fall within a clade formed by eleven species of the 'Rhizobium tropici group' (R. tropici, R. leucaenae, R. lusitanum, R. multihospitium, R. miluonense, R. hainanense, R. calliandrae, R. mayense, R. jaguaris, R. rhizogenes and R. freirei) (Ribeiro et al, 2012;Dall'Agnol et al, 2013) (Fig. 1).…”

“…All strains used in commercial inoculants in Brazil with common bean belong to R. tropici [SEMIA 4077 T (5CIAT 899 T ) and SEMIA 4088 (5H 12)] or R. freirei [SEMIA 4080 T (5PRF 81 T )], and show genetic stability and high tolerance of stressful environmental conditions (Hungria et al, 2000Dall'Agnol et al, 2013). In our studies, we have identified other strains, including PRF 35 T , PRF 54, CPAO 1135 and H 52, which show high efficiency in N 2 fixation with common bean, and are classified as R. tropici (Hungria et al, 2000Mostasso et al, 2002;Pinto et al, 2007).…”