Systematic and Applied Microbiology 30 (2007) 280–290 Ensifer mexicanus sp. nov. a new species nodulating Acacia angustissima (Mill.) Kuntze in Mexico Lourdes Lloret a , Ernesto Ormen˜o-Orrillo a , Reiner Rinco´n b , Julio Martı´nez-Romero a , Marco Antonio Rogel-Herna´ndez a , Esperanza Martı´nez-Romero a,à a Centro de Ciencias Geno´micas, UNAM, Apdo. Postal 565-A, CP 62251, Cuernavaca, Morelos, Mexico b Instituto Tecnolo´gico de Tuxtla Gutie´rrez, Carretera Panamericana Km. 1080, Tuxtla Gutie´rrez, Apdo. Postal 559, Chiapas, Mexico Received 31 October 2006 Abstract A new lineage of Ensifer nodulating the American legume Acacia angustissima in the tropical forest of Chiapas and Morelos, Mexico is described. Bacteria were identified as Ensifer with ssb or nolR specific primers. Phylogenetic analysis with partial sequences of the five chromosomal genes gyrA, nolR, recA, rpoB and rrs revealed that this new lineage is related to African Ensifer terangae. The results of total DNA–DNA hybridization and selected phenotypic tests among the A. angustissima strains and E. terangae indicated that they belong to different species. The phylogeny with the symbiotic nifH gene also separates this group as a different clade but with close affinities to bacteria belonging to the genus Ensifer isolated from American hosts. ITTG R7 T ( ¼ CFN ER1001, HAMBI 2910, CIP 109033, ATCC BAA-1312, DSM18446) is the type strain of a new species for which the name Ensifer mexicanus sp. nov. is proposed. r 2006 Elsevier GmbH. All rights reserved. Keywords: Phylogeny; Taxonomy; Systematics; Legume symbiont; Nitrogen fixation; Acacia angustissima; Sinorhizobium; Ensifer, sp. nov Introduction Several genera within the a-Proteobacteria [43,49,65] as well as a few genera of b-Proteobacteria [5,32] induce the formation of nodules and fix nitrogen in the roots and rarely in the stems of leguminous plants, providing nitrogen that supports plant growth. Among these, the a-Proteobacterial genus Sinorhizobium, now renamed as Ensifer (because of the joining of Sinorhizobium and Ensifer genera into the same genus [63,67]), includes over 10 species isolated from a wide range of legume hosts. Acacia is one of the largest genera of the Leguminosae and underwent successive radiations in the Southern continents with Australia being the largest diversifica- tion center and the tropics of the Americas among the oldest. Acacia angustissima has a broad geographical distribution ranging from the Southern United States to Costa Rica. It is considered a promising tree species to restore eroded areas. Acacias have been reported to be nodulated by Ensifer terangae bv. acaciae, Ensifer saheli bv. acaciae ARTICLE IN PRESS www.elsevier.de/syapm 0723-2020/$ - see front matter r 2006 Elsevier GmbH. All rights reserved. doi:10.1016/j.syapm.2006.12.002 Abbreviations: PCR: Polymerase chain reaction; rep-PCR: repetitive extragenic palindromic PCR, ERIC: Enterobacterial repetitive inter- genic consensus, MLEE: Multilocus enzyme electrophoresis à Corresponding author. Tel.: +52 777 3 13 16 97; fax: +52 777 3 17 55 81. E-mail address: emartine@ccg.unam.mx (E. Martı´nez-Romero).