National Center for Biotechnology Information, National Library of Medicine. National Institutes of Health, Bethesda, Maryland, USA.
Environ Microbiol. 2024 Apr;26(4):e16630. doi: 10.1111/1462-2920.16630.
Horizontal gene transfer (HGT) is a fundamental process in prokaryotic evolution, contributing significantly to diversification and adaptation. HGT is typically facilitated by mobile genetic elements (MGEs), such as conjugative plasmids and phages, which often impose fitness costs on their hosts. However, a considerable number of bacterial genes are involved in defence mechanisms that limit the propagation of MGEs, suggesting they may actively restrict HGT. In our study, we investigated whether defence systems limit HGT by examining the relationship between the HGT rate and the presence of 73 defence systems across 12 bacterial species. We discovered that only six defence systems, three of which were different CRISPR-Cas subtypes, were associated with a reduced gene gain rate at the species evolution scale. Hosts of these defence systems tend to have a smaller pangenome size and fewer phage-related genes compared to genomes without these systems. This suggests that these defence mechanisms inhibit HGT by limiting prophage integration. We hypothesize that the restriction of HGT by defence systems is species-specific and depends on various ecological and genetic factors, including the burden of MGEs and the fitness effect of HGT in bacterial populations.
水平基因转移（HGT）是原核生物进化的一个基本过程，对生物多样性和适应性的形成有重要贡献。HGT 通常由移动遗传元件（MGE）介导，如可移动质粒和噬菌体，这些 MGE 往往会给宿主带来适应度代价。然而，许多细菌基因参与了限制 MGE 传播的防御机制，这表明它们可能会主动限制 HGT。在我们的研究中，我们通过研究 12 种细菌中 HGT 率与 73 种防御系统之间的关系，来检验防御系统是否通过限制 HGT 来促进物种进化。我们发现，只有六种防御系统，其中三种是不同的 CRISPR-Cas 亚型，与物种进化尺度上的基因获得率降低有关。与没有这些系统的基因组相比，这些防御系统的宿主往往具有较小的泛基因组大小和较少的噬菌体相关基因。这表明这些防御机制通过限制前噬菌体的整合来抑制 HGT。我们假设，防御系统对 HGT 的限制是物种特异性的，取决于各种生态和遗传因素，包括 MGE 的负担和 HGT 在细菌种群中的适应度效应。
