Andronov E E, Onishchuk O P, Kurchak O N, Provorov N A
Mikrobiologiia. 2014 Jul-Aug;83(4):500-8.
High-throughput sequencing of the amplicon gene library revealed variations in the population structure of clover rhizobia (Rhizobium leguminosarum bv. trifolii) upon transition from soil into the root nodules of the host plant (Trifolium-hybridum). Analysis of rhizobial-diversity using the nodA gene revealed 3258 and 1449 nucleotide sequences (allelic-variants) for the soil and root nodule population, respectively. They were combined into 29 operational taxonomic units (OTU) according to the 97% identity level; 24 OTU were. foundin the soil population, 12 were present in the root nodulepopulation, and 7 were common. The predominant OTE13 (77.4 and 91.5% of the soil and root nodule populations, respectively) contained 155 and -200 variants of the soil and root nodule populations, respectively, with the nucleotide diversity increasing significantly upon the "soil-->root" transition. The "moving window" approach was used to reveal the sites of the nodA gene in which polymorphism, including that associated with increased frequency of non-synonymous substitution frequency, increased sharply upon transition from soil into root nodiles. PCR analysis of the IGS genotypes of individual strains revealed insignificant changes in rhizobial diversity upon transition from soil into root nodules. These results indicate that acceleration of rhizobial evolutioin in the course of symbiosis may be associated with development of highly polymorphic virulent:subpopulations subjected to directional selection in the "plant-soil" system.
对扩增子基因文库进行高通量测序，结果显示，三叶草根瘤菌（豆科根瘤菌三叶草生物型）从土壤进入宿主植物（杂种车轴草）根瘤的过程中，其种群结构发生了变化。利用nodA基因分析根瘤菌多样性，结果显示，土壤和根瘤种群分别有3258个和1449个核苷酸序列（等位基因变体）。根据97%的同一性水平，它们被合并为29个操作分类单元（OTU）；在土壤种群中发现了24个OTU，在根瘤种群中发现了12个OTU，7个是共有的。占主导地位的OTU13（分别占土壤和根瘤种群的77.4%和91.5%）分别包含155个和200个土壤和根瘤种群的变体，从“土壤→根”转变后，核苷酸多样性显著增加。采用“移动窗口”方法揭示nodA基因中多态性位点，包括与非同义替换频率增加相关的位点，从土壤进入根瘤后多态性急剧增加。对单个菌株的IGS基因型进行PCR分析，结果显示从土壤进入根瘤后根瘤菌多样性变化不显著。这些结果表明，共生过程中根瘤菌进化加速可能与“植物-土壤”系统中经过定向选择的高多态性致病亚种群的发育有关。
