Department of Crop Sciences, Tshwane University of Technology, Pretoria, South Africa.
Department of Chemistry, Tshwane University of Technology, Private Bag X680, Pretoria, 0001, South Africa.
Microb Ecol. 2021 Oct;82(3):688-703. doi: 10.1007/s00248-021-01684-0. Epub 2021 Feb 19.
Rhizobial microsymbionts of grain legumes are ubiquitous in soils and exhibit a wide range of diversity with respect to colony morphology, genetic variability, biochemical characteristics, and phylogenetic relationships. This study assessed the phylogenetic positions of rhizobial microsymbionts of Bambara groundnut from Eswatini exhibiting variations in morpho-physiology, adaptive characteristics, and N-fixing efficiency. The isolates' ERIC-PCR profiles revealed the presence of high genetic variation among them. These test isolates also exhibited differences in pH tolerance and IAA production. Multilocus sequence analysis based on the 16S rRNA, atpD, glnII, gyrB, and recA gene sequences of representative test isolates closely aligned them to the type strains of Bradyrhizobium arachidis, B. manausense, B. guangdongense, B. elkanii, and B. pachyrhizi. However, some isolates showed a high divergence from the known reference type strains, indicating that they may represent species yet to be properly characterized and described. Functional characterization in the glasshouse revealed that most of the isolates from the contrasting Agro-ecologies of Eswatini were efficient in N fixation, and therefore elicited greater stomatal conductance and photosynthetic rates in the homologous Bambara groundnut. Of the 75 isolates tested, 51% were more effective than the commercial Bradyrhizobium sp. strain CB756, with relative symbiotic effectiveness ranging from 138 to 308%. The findings of this study indicated that the analysis of housekeeping genes and functional traits of Bambara-nodulating microsymbionts can provide a clear view for understanding and predicting rhizobial community structure across environmental gradients.
根瘤菌微生物共生体在土壤中无处不在，其在菌落形态、遗传变异性、生化特性和系统发育关系等方面表现出广泛的多样性。本研究评估了在形态生理学、适应特性和固氮效率方面表现出变异的斯威士兰竹豆根瘤菌微生物共生体的系统发育地位。分离物的 ERIC-PCR 图谱显示它们之间存在高度遗传变异。这些测试分离物在 pH 耐受性和 IAA 产生方面也表现出差异。基于代表测试分离物的 16S rRNA、atpD、glnII、gyrB 和 recA 基因序列的多位点序列分析，将它们与花生根瘤菌、曼氏根瘤菌、广东根瘤菌、埃尔坎根瘤菌和厚荚相思根瘤菌的模式菌株紧密对齐。然而，一些分离物与已知的参考模式菌株表现出高度的分化，表明它们可能代表尚未得到适当描述和描述的物种。温室功能表征表明，来自斯威士兰 contrasting Agro-ecologies 的大多数分离物在固氮方面效率很高，因此在同源竹豆中引起更大的气孔导度和光合速率。在测试的 75 个分离物中，有 51%比商业的花生根瘤菌菌株 CB756 更有效，相对共生有效性范围为 138 到 308%。本研究的结果表明，分析竹豆结瘤微生物共生体的看家基因和功能特性可以为理解和预测环境梯度上的根瘤菌群落结构提供清晰的认识。
