Reclassification of Rhizobium tropici type A strains as Rhizobium leucaenae sp. nov. Renan Augusto Ribeiro, 1,2 3 Marco A. Rogel, 3 3 Aline Lo ´ pez-Lo ´ pez, 3 Ernesto Ormen ˜ o-Orrillo, 1 Fernando Gomes Barcellos, 4 Julio Martı ´nez, 3 Fabiano Lopes Thompson, 5 Esperanza Martı ´nez-Romero 3 and Mariangela Hungria 1 Correspondence Ernesto Ormen ˜ o-Orrillo eormeno.orrillo@gmail.com 1 Embrapa Soja, Cx. Postal 231, 86001-970, Londrina, Parana ´ , Brazil 2 Universidade Estadual de Londrina, Department of Microbiology, Cx. Postal 60001, 86051-990, Londrina, Parana ´ , Brazil 3 Centro de Ciencias Geno ´ micas, Universidad Nacional Auto ´ noma de Me ´ xico, Cuernavaca, Morelos, Mexico 4 Universidade Paranaense – UNIPAR, Cx. Postal 224, 87502-210, Umuarama, Parana ´ , Brazil 5 UFRJ, Center of Health Sciences, Institute of Biology, Cx. Postal 68011, 21944-970, Rio de Janeiro, Brazil Rhizobium tropici is a well-studied legume symbiont characterized by high genetic stability of the symbiotic plasmid and tolerance to tropical environmental stresses such as high temperature and low soil pH. However, high phenetic and genetic variabilities among R. tropici strains have been largely reported, with two subgroups, designated type A and B, already defined within the species. A polyphasic study comprising multilocus sequence analysis, phenotypic and genotypic characterizations, including DNA–DNA hybridization, strongly supported the reclassification of R. tropici type A strains as a novel species. Type A strains formed a well-differentiated clade that grouped with R. tropici, Rhizobium multihospitium, Rhizobium miluonense, Rhizobium lusitanum and Rhizobium rhizogenes in the phylogenies of the 16S rRNA, recA, gltA, rpoA, glnII and rpoB genes. Several phenotypic traits differentiated type A strains from all related taxa. The novel species, for which the name Rhizobium leucaenae sp. nov. is proposed, is a broad host range rhizobium being able to establish effective root-nodule symbioses with Leucaena leucocephala, Leucaena esculenta, common beans (Phaseolus vulgaris) and Gliricidia sepium. Strain CFN 299 T (5USDA 9039 T 5LMG 9517 T 5CECT 4844 T 5JCM 21088 T 5IAM 14230 T 5SEMIA 4083 T 5CENA 183 T 5UMR1026 T 5CNPSo 141 T ) is designated the type strain of Rhizobium leucaenae sp. nov. A group of bacterial species, collectively known as rhizobia, can induce the formation of specific structures, named nodules, on the roots of legumes eliciting a symbiotic process in which the rhizobia fix atmospheric nitrogen and supply it to the plant. Interest in the use of rhizobia as biofertilizers in agriculture has promoted studies on their diversity and the description of a large number of rhizobial species. Rhizobium tropici is a broad host range rhizobial species that was isolated from Leucaena spp. nodules in Brazil (Hungria et al., 2000; Martı´nez-Romero et al., 1991), and from Gliricidia sepium (Acosta-Dura ´n & Martı´nez- Romero, 2002) and Acaciella angustissima (Rinco ´ n-Rosales et al., 2009) in Mexico. The species has also been isolated from common bean (Phaseolus vulgaris) nodules in several countries (Amarger et al., 1994; Anyango et al., 1995; Diouf et al., 2000; Grange & Hungria, 2004; Pinto et al., 2007). R. tropici has been used as an efficient inoculant for beans in the tropics, due to its high tolerance to environmentally stressful conditions and its high genetic stability (Hungria et al., 2000, 2003). R. tropici, reported in 1991 (Martı´nez-Romero et al., 1991), was the first description of a rhizobial species to include 16S rRNA gene sequence analysis. At that time, in spite of evidence that supported the proposal of two species from 3These authors contributed equally to this work. The GenBank/EMBL/DDBJ accession numbers for the 49 sequences reported in this paper are provided in Table S1 (available in IJSEM Online). Five supplementary tables and seven supplementary figures are available with the online version of this paper. International Journal of Systematic and Evolutionary Microbiology (2012), 62, 1179–1184 DOI 10.1099/ijs.0.032912-0 032912 G 2012 IUMS Printed in Great Britain 1179