Table_1_A Genomotaxonomy View of the Bradyrhizobium Genus.pdf

Whole genome analysis of the Bradyrhizobium genus using average nucleotide identity (ANI) and phylogenomics showed the genus to be essentially monophyletic with seven robust groups within this taxon that includes nitrogen-fixing nodule forming bacteria as well as free living strains. Despite the wide genetic diversity of these bacteria no indication was found to suggest that the Bradyrhizobium genus have to split in different taxa. Bradyrhizobia have larger genomes than other genera of the Bradyrhizobiaceae family, probably reflecting their metabolic diversity and different lifestyles. Few plasmids in the sequenced strains were revealed from rep gene analysis and a relatively low proportion of the genome is devoted to mobile genetic elements. Sequence diversity of recA and glnII gene metadata was used to theoretically estimate the number of existing species and to predict how many would exist. There may be many more species than those presently described with predictions of around 800 species in nature. Different arguments are presented suggesting that nodulation might have arose in the ancestral genus Bradyrhizobium.

利用平均核苷酸同源性（average nucleotide identity, ANI）与系统发育基因组学方法对慢生根瘤菌属（Bradyrhizobium）开展全基因组分析，结果显示该类群本质上为单系群，其下包含7个稳健的演化支；该类群涵盖固氮结瘤细菌与自由生活菌株。尽管此类细菌具有广泛的遗传多样性，但未发现任何证据支持将慢生根瘤菌属拆分为多个独立分类单元。慢生根瘤菌的基因组尺寸大于慢生根瘤菌科（Bradyrhizobiaceae）其他属的菌株，这一特征可能反映了其代谢多样性与多样化的生活方式。通过rep基因分析，在已测序菌株中仅检测到少量质粒，且基因组中移动遗传元件的占比相对较低。研究人员借助recA与glnII基因的序列元数据，从理论层面估算了当前已发现的物种数量，并预测了自然界中潜在的物种总数。自然界中实际存在的物种数量或远多于目前已描述的类群，相关预测显示其总数约为800种。多项论证表明，结瘤能力可能起源于慢生根瘤菌属的祖先类群。