Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand.
School of Pharmacy and Biomedical Science, Curtin University, Perth, Australia.
Microb Genom. 2020 Sep;6(9). doi: 10.1099/mgen.0.000426. Epub 2020 Aug 26.
is a genus of soil bacteria, some isolates of which form an endosymbiotic relationship with diverse legumes of the Loteae tribe. The symbiotic genes of these mesorhizobia are generally carried on integrative and conjugative elements termed symbiosis islands (ICESyms). strains that nodulate spp. have been divided into host-range groupings. Group I (GI) strains nodulate and ecotype Gifu, while group II (GII) strains have a broader host range, which includes . To identify the basis of this extended host range, and better understand and ICESym genomics, the genomes of eight strains were completed using hybrid long- and short-read assembly. Bioinformatic comparison with previously sequenced mesorhizobia genomes indicated host range was not predicted by genospecies but rather by the evolutionary relationship between ICESym symbiotic regions. Three radiating lineages of Loteae ICESyms were identified on this basis, which correlate with spp. host-range grouping and have lineage-specific gene complements. Pangenomic analysis of the completed GI and GII ICESyms identified 155 core genes (on average 30.1 % of a given ICESym). Individual GI or GII ICESyms carried diverse accessory genes with an average of 34.6 % of genes unique to a given ICESym. Identification and comparative analysis of NodD symbiotic regulatory motifs - boxes - identified 21 branches across the NodD regulons. Four of these branches were associated with seven genes unique to the five GII ICESyms. The boxes preceding the host-range gene in GI and GII ICESyms were disparate, suggesting regulation of may differ between GI and GII ICESyms. The broad host-range determinant(s) of GII ICESyms that confer nodulation of are likely present amongst the 53 GII-unique genes identified.
是土壤细菌的一个属，其中一些分离株与 Loteae 部落的多种豆科植物形成共生关系。这些中慢生根瘤菌的共生基因通常携带在整合和共轭元件上，称为共生岛 (ICESyms)。能够结瘤 种的 菌株已被分为宿主范围分组。第 I 组 (GI) 菌株结瘤 和 吉富型，而第 II 组 (GII) 菌株具有更广泛的宿主范围，其中包括 。为了确定这种扩展宿主范围的基础，并更好地了解 和 ICESym 基因组学，使用混合长读和短读组装完成了 8 个 菌株的基因组。与先前测序的中慢生根瘤菌基因组的生物信息比较表明，宿主范围不是由 种预测的，而是由 ICESym 共生区的进化关系决定的。在此基础上，确定了三个辐射状的 Loteae ICESym 谱系，它们与 spp. 宿主范围分组相关，并具有谱系特异性的 基因补充。完成的 GI 和 GII ICESym 的泛基因组分析确定了 155 个核心基因（平均占给定 ICESym 的 30.1%）。单个 GI 或 GII ICESym 携带不同的辅助基因，平均有 34.6%的基因是给定 ICESym 所特有的。共生调节模体 NodD 的识别和比较分析 - 盒子 - 在 NodD 调控子中鉴定出 21 个分支。这些分支中的 4 个与五个 GII ICESyms 中特有的七个基因相关。GI 和 GII ICESyms 中 基因之前的 盒子存在差异，表明 GI 和 GII ICESyms 中 的调节可能不同。赋予 GII ICESyms 结瘤 能力的广泛宿主范围决定因素可能存在于鉴定出的 53 个 GII 特有基因中。
