Laboratory of Legumes and Sustainable Agroecosystems, Centre of Biotechnology of Borj-Cédria, BP 901 Hammam-lif 2050, Tunisia.
Agriculture and Agri-Food Canada, 4902 Victoria Avenue North, Vineland Station, Ontario L0R 2E0, Canada.
Syst Appl Microbiol. 2022 Jul;45(4):126343. doi: 10.1016/j.syapm.2022.126343. Epub 2022 Jun 18.
Acacia saligna is an invasive alien species that has the ability to establish symbiotic relationships with rhizobia. In the present study, genotypic and symbiotic diversity of native rhizobia associated with A. saligna in Tunisia were studied. A total of 100 bacterial strains were selected and three different ribotypes were identified based on rrs PCR-RFLP analysis. Sequence analyses of rrs and four housekeeping genes (recA, atpD, gyrB and glnII) assigned 30 isolates to four putative new lineages and a single strain to Sinorhizobium meliloti. Thirteen slow-growing isolates representing the most dominant IGS (intergenic spacer) profile clustered distinctly from known rhizobia species within Bradyrhizobium with the closest related species being Bradyrhizobium shewense and Bradyrhizobium niftali, which had 95.17% and 95.1% sequence identity, respectively. Two slow-growing isolates, 1AS28L and 5AS6L, had B. frederekii as their closest species with a sequence identity of 95.2%, an indication that these strains could constitute a new lineage. Strains 1AS14I, 1AS12I and 6AS6 clustered distinctly from known rhizobia species but within the Rhizobium leguminosarum complex (Rlc) with the most closely related species being Rhizobium indicum with 96.3% sequence identity. Similarly, the remaining 11 strains showed 96.9 % and 97.2% similarity values with R. changzhiense and R. indicum, respectively. Based on nodC and nodA phylogenies and cross inoculation tests, these 14 strains of Rlc species clearly diverged from strains of Sinorhizobium and Rlc symbiovars, and formed a new symbiovar for which the name sv. "salignae" is proposed. Bacterial strains isolated in this study that were taxonomically assigned to Bradyrhizobium harbored different symbiotic genes and the data suggested a new symbiovar, for which sv. "cyanophyllae" is proposed. Isolates formed effective nodules on A. saligna.
金合欢树是一种具有与根瘤菌建立共生关系能力的入侵外来物种。本研究研究了突尼斯金合欢树共生的土著根瘤菌的基因型和共生多样性。共选择了 100 株细菌菌株，并根据 rrs PCR-RFLP 分析鉴定了 3 种不同的核糖体类型。rrs 和 4 个看家基因（recA、atpD、gyrB 和 glnII）的序列分析将 30 个分离株分配到 4 个假定的新谱系中，单个菌株分配到 Sinorhizobium meliloti 中。13 个生长缓慢的分离株代表最主要的 IGS（基因间间隔）图谱，与 Bradyrhizobium 内的已知根瘤菌物种明显聚类，最接近的相关物种是 Bradyrhizobium shewense 和 Bradyrhizobium niftali，它们的序列同一性分别为 95.17%和 95.1%。两个生长缓慢的分离株 1AS28L 和 5AS6L，与 B. frederekii 的亲缘关系最近，序列同一性为 95.2%，表明这些菌株可能构成一个新谱系。菌株 1AS14I、1AS12I 和 6AS6 与已知的根瘤菌物种明显聚类，但在 Rhizobium leguminosarum 复合体（Rlc）内，最接近的相关物种是 Rhizobium indicum，序列同一性为 96.3%。同样，其余 11 株菌与 R. changzhiense 和 R. indicum 的相似性分别为 96.9%和 97.2%。根据 nodC 和 nodA 系统发育和交叉接种试验，这些 14 株 Rlc 物种的菌株明显与 Sinorhizobium 和 Rlc 共生变种的菌株分化，并形成了一个新的共生变种，建议命名为 sv. "salignae"。本研究中分离的属于 Bradyrhizobium 的细菌菌株携带不同的共生基因，数据表明存在一个新的共生变种，建议命名为 sv. "cyanophyllae"。分离株在金合欢树上形成有效的根瘤。
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