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Applied and Environmental Microbiology, May 2007, p. 3254-3264, Vol. 73, No. 10
0099-2240/07/$08.00+0     doi:10.1128/AEM.02125-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Diversification of Lupine Bradyrhizobium Strains: Evidence from Nodulation Gene Trees ^,

Tomasz Stpkowski,^1* Colin E. Hughes,² Ian J. Law,³ ukasz Markiewicz,¹ Dorota Gurda,¹ Agnieszka Chlebicka,¹ and Lionel Moulin⁴

Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61 704 Pozna, Poland,¹ Department of Plant Sciences, University of Oxford, South Parks Rd., Oxford OX1 3RB, United Kingdom,² Plant Protection Research Institute, Private Bag X134, Queenswood 0121, South Africa,³ Laboratoire des Symbioses Tropicales et Méditerranéennes, IRD-CIRAD-INRA-UMII, 34398 Montpellier Cedex 5, France⁴

Received 8 September 2006/ Accepted 20 March 2007

Bradyrhizobium strains isolated in Europe from Genisteae and serradella legumes form a distinct lineage, designated clade II, on nodulation gene trees. Clade II bradyrhizobia appear to prevail also in the soils of Western Australia and South Africa following probably accidental introduction with seeds of their lupine and serradella hosts. Given this potential for dispersal, we investigated Bradyrhizobium isolates originating from a range of native New World lupines, based on phylogenetic analyses of nodulation (nodA, nodZ, noeI) and housekeeping (atpD, dnaK, glnII, recA) genes. The housekeeping gene trees revealed considerable diversity among lupine bradyrhizobia, with most isolates placed in the Bradyrhizobium japonicum lineage, while some European strains were closely related to Bradyrhizobium canariense. The nodA gene tree resolved seven strongly supported groups (clades I to VII) that correlated with strain geographical origins and to some extent with major Lupinus clades. All European strains were placed in clade II, whereas only a minority of New World strains was placed in this clade. This work, as well as our previous studies, suggests that clade II diversified predominately in the Old World, possibly in the Mediterranean. Most New World isolates formed subclade III.2, nested in a large "pantropical" clade III, which appears to be New World in origin, although it also includes strains originating from nonlupine legumes. Trees generated using nodZ and noeI gene sequences accorded well with the nodA tree, but evidence is presented that the noeI gene may not be required for nodulation of lupine and that loss of this gene is occurring.

Published ahead of print on 30 March 2007.

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