Legume-nodulating betaproteobacteria: diversity, host range and future prospects

Prasad Gyaneshwar, A. Hirsch, Lionel Moulin, Wen-Ming Chen, Geoffrey N. Elliott, Cyril Bontemps, Paulina Estrada de los Santos, Eduardo Gross, Janet I. Sprent, Peter Young, Euan K. James

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Rhizobia form specialized nodules on the roots of legumes (family Fabaceae) and fix nitrogen in exchange for carbon from the host plant. Although the majority of legumes form symbioses with members of genus Rhizobium and its relatives in class Alphaproteobacteria, some legumes, such as those in the large genus Mimosa, are nodulated pre- dominantly by betaproteobacteria in the genera Burkhold- eria and Cupriavidus. The principal centers of diversity of these bacteria are in central Brazil and South Africa. Mo- lecular phylogenetic studies have shown that betaproteo- bacteria have existed as legume symbionts for approxi- mately 50 million years, and that, although they have a common origin, the symbiosis genes in both subclasses have evolved separately since then. Additionally, some spe- cies of genus Burkholderia, such as B. phymatum, are highly promiscuous, effectively nodulating several impor- tant legumes, including common bean (Phaseolus vulgaris). In contrast to genus Burkholderia, only one species of ge- nus Cupriavidus (C. taiwanensis) has so far been shown to nodulate legumes. The recent availability of the genome sequences of C. taiwanensis, B. phymatum, and B. tuberum has paved the way for a more detailed analysis of the evolu- tionary and mechanistic differences between nodulating strains of alpha- and betaproteobacteria. Initial analyses of genome sequences have suggested that plant-associated Burkholderia spp. have lower G+C contents than Burkholderia spp. that are opportunistic human pathogens, thus supporting previous suggestions that the plant- and human-associated groups of Burkholderia actually belong in separate genera.
Original languageEnglish
Pages (from-to)1276-1288
Number of pages13
Issue number11
Publication statusPublished - Nov 2011

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