Rhizobium gone native: unexpected plasmid stability of indigenous Rhizobium leguminosarum.
Rhizobium gone native: unexpected plasmid stability of indigenous Rhizobium leguminosarum.
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DOI：
10.1073/pnas.94.10.5483
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发表时间：
1997-05
影响因子：
11.1
通讯作者：
J. Wernegreen;Ethelynda E. Harding;Margaret A. Riley
中科院分区：
文献类型：
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作者：
J. Wernegreen;Ethelynda E. Harding;Margaret A. Riley
细菌质粒的横向转移被认为在微生物进化和种群动态中发挥重要作用。然而，这一假设主要基于对医学或农业上重要的细菌物种的调查。为了探索横向转移在不处于密集的、人类介导的选择下的细菌系统进化中的作用，我们检查了原生根瘤菌（豆科植物的固氮共生体）的质粒编码基因座和染色体基因座的基因型关联。为此，在质粒编码的共生（sym）区域（结瘤AB和结瘤CIJT位点）和不参与与豆科植物共生的重复染色体位点对本地三叶草结瘤同域物种的豆根瘤菌菌株进行了遗传学表征。限制性片段长度多态性分析用于区分质粒和染色体位点的遗传群体。使用chi2分析确定主要sym和染色体基因型之间的相关性以及基因型在宿主植物物种和采样地点之间的分布。与之前的研究结果相反，主要 sym 质粒和染色体遗传群体之间存在严格的关联，表明主要根瘤菌染色体类型之间缺乏成功的 sym 质粒转移。这些数据表明，先前对农业环境中 sym 质粒转移的观察可能严重高估了未受人类活动影响的系统中的成功接合率。此外，根瘤菌基因型在宿主植物物种和采样点之间的非随机分布表明这两个因素在塑造根瘤菌种群动态中的重要性。
Lateral transfer of bacterial plasmids is thought to play an important role in microbial evolution and population dynamics. However, this assumption is based primarily on investigations of medically or agriculturally important bacterial species. To explore the role of lateral transfer in the evolution of bacterial systems not under intensive, human-mediated selection, we examined the association of genotypes at plasmid-encoded and chromosomal loci of native Rhizobium, the nitrogen-fixing symbiont of legumes. To this end, Rhizobium leguminosarum strains nodulating sympatric species of native Trifolium were characterized genetically at plasmid-encoded symbiotic (sym) regions (nodulation AB and nodulation CIJT loci) and a repeated chromosomal locus not involved in the symbiosis with legumes. Restriction fragment length polymorphism analysis was used to distinguish genetic groups at plasmid and chromosomal loci. The correlation between major sym and chromosomal genotypes and the distribution of genotypes across host plant species and sampling location were determined using chi2 analysis. In contrast to findings of previous studies, a strict association existed between major sym plasmid and chromosomal genetic groups, suggesting a lack of successful sym plasmid transfer between major Rhizobium chromosomal types. These data indicate that previous observations of sym plasmid transfer in agricultural settings may seriously overestimate the rates of successful conjugation in systems not impacted by human activities. In addition, a nonrandom distribution of Rhizobium genotypes across host plant species and sampling site demonstrates the importance of both factors in shaping Rhizobium population dynamics.