The Mediterranean world is the cradle for the diversification of a large number of plant species, including legumes belonging to the Tribe Genisteae. Nodule bacteria from three species of Genista legumes indigenous to northwestern Africa (G. ferox, G. numidica, G. tricuspidata) were sampled across a 150 km region of Algeria in order to investigate symbiotic relationships. Partial 23S rRNA sequences from 107 isolates indicated that Bradyrhizobium was the predominant symbiont genus (96% of isolates), with the remainder belonging to Rhizobium or Mesorhizobium. A multilocus sequence analysis on 46 Bradyrhizobium strains using seven housekeeping (HK) genes showed that strains were differentiated into multiple clades with affinities to seven species: B. canariense (17 isolates), B. japonicum (2), B. ottawaense (2), B. cytisi/B. rifense (9), ‘B. valentinum’ (5), and B. algeriense (11). Extensive discordance between the HK gene phylogeny and a tree for four loci in the symbiosis island (SI) region implied that horizontal transfer of SI loci has been common. Cases of close symbiont relationship across pairs of legumes hosts were evident, with 33% of isolates having as their closest relative a strain sampled from a different Genista species. Nevertheless, tree permutation tests also showed that there was substantial host-related phylogenetic clustering. Thus, each of the three Genista hosts utilized a measurably different array of bacterial lineages.

地中海世界是多种植物种类（包括属于部落Genisteae的豆类）多样化的摇篮。从三个品种的根瘤菌染料木豆科植物原产于非洲西北部（G.芡，G. numidica，G.爬山虎）的跨越阿尔及利亚的150公里区域，以便调查共生关系采样。来自107个分离株的部分23S rRNA序列表明，缓生根瘤菌是主要的共生菌属（占分离株的96％），其余的属于根瘤菌或中生根瘤菌。46根瘤菌的多位点序列分析使用七个持家株（HK）的基因表明，菌株分化成具有亲和力多个进化枝到七个种类：B. canariense（17株），根瘤菌（2），B. ottawaense（2），B. cytisi / B. rifense（9），“ B。valentinum'（5）和B. algeriense（11）。HK基因系统发育与共生岛（SI）区域中四个基因座的树之间存在巨大的不一致，这表明SI基因座的水平转移已很普遍。跨豆类宿主对存在明显共生关系的案例很明显，其中33％的分离株具有从不同Genista取样的菌株作为其最亲缘关系。种类。但是，树排列测试也显示存在大量与宿主相关的系统发生聚类。因此，三个Genista宿主中的每一个都利用了不同程度的细菌谱系。