Genomes from sixty-six Bradyrhizobium spp. isolates from forest soils from across North America were sequenced, representing one of the most abundant taxa in across all forest soils.. Genomic Diversity of Abundant Bradyrhizobium from Forest Soils Across North America

Members of Bradyrhizobiaceae and in particular Bradyrhizobium are one of the most abundant taxonomic groups identified through sequencing surveys of forest soil bacterial communities. In general they are one of the most abundant soil bacterial groups across a variety of environments. We isolated and sequenced 66 Bradyrhizobium from organic and mineral layers of forest soils in British Columbia, Ontario, California and Texas to characterize the core genome relative to the diversity of the pangenome. Contrary to expectations, none of the assembled isolate genomes possessed genes encoding nitrogenases. The pangenome was extensive across sites and differences were detected in isolates from mineral vs. organic layers. Validation of substrate-utilization and other features of these isolates was made challenging by the nature of these slow-growing organisms which generally fail to grow in liquid culture. These genomes provide a comprehensive insight into these poorly understood and highly abundant soil bacteria.

慢生根瘤菌科（Bradyrhizobiaceae）成员，尤其是慢生根瘤菌属（Bradyrhizobium），是通过森林土壤细菌群落测序调查所鉴定出的丰度最高的类群之一。总体而言，在多种环境中，它们均为丰度最高的土壤细菌类群之一。本研究从不列颠哥伦比亚省、安大略省、加利福尼亚州以及得克萨斯州的森林土壤有机层与矿质层中分离得到66株慢生根瘤菌并完成测序，旨在结合泛基因组（pangenome）多样性解析其核心基因组（core genome）特征。与预期相悖的是，所有组装完成的分离株基因组均未携带编码固氮酶（nitrogenases）的基因。不同采样点的泛基因组规模庞大，且矿质层分离株与有机层分离株之间存在显著差异。由于这类微生物生长缓慢且通常无法在液体培养基中增殖，验证这些分离株的底物利用能力及其他特征颇具挑战。本研究获得的基因组为深入解析这类认知匮乏但丰度极高的土壤细菌提供了全面视角。