Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA.
Department of Evolution Ecology and Organismal Biology, University of California Riverside, Riverside, CA 92521, USA.
Genome Biol Evol. 2022 May 31;14(6). doi: 10.1093/gbe/evac078.
Acquisition of mobile genetic elements can confer novel traits to bacteria. Some integrative and conjugative elements confer upon members of Bradyrhizobium the capacity to fix nitrogen in symbiosis with legumes. These so-called symbiosis integrative conjugative elements (symICEs) can be extremely large and vary as monopartite and polypartite configurations within chromosomes of related strains. These features are predicted to impose fitness costs and have defied explanation. Here, we show that chromosome architecture is largely conserved despite diversity in genome composition, variations in locations of attachment sites recognized by integrases of symICEs, and differences in large-scale chromosomal changes that occur upon integration. Conversely, many simulated nonnative chromosome-symICE combinations are predicted to result in lethal deletions or disruptions to architecture. Findings suggest that there is compatibility between chromosomes and symICEs. We hypothesize that the size and structural flexibility of symICEs are important for generating combinations that maintain chromosome architecture across a genus of nitrogen-fixing bacteria with diverse and dynamic genomes.
移动遗传元件的获得可以赋予细菌新的特性。一些整合和共轭元件使慢生根瘤菌能够在与豆科植物共生固氮。这些所谓的共生整合共轭元件（symICEs）可以非常大，并在相关菌株的染色体中呈现单分体和多分体构型的变化。这些特征预计会带来适应性成本，并且难以解释。在这里，我们表明，尽管基因组组成存在多样性、symICEs 整合酶识别的附着位点的位置存在变化以及整合时发生的大规模染色体变化存在差异，但染色体结构在很大程度上是保守的。相反，许多模拟的非天然染色体-symICE 组合预计会导致致命的缺失或破坏结构。研究结果表明，染色体和 symICEs 之间存在兼容性。我们假设 symICEs 的大小和结构灵活性对于产生组合很重要，这些组合可以在具有多样化和动态基因组的固氮细菌属中维持染色体结构。
