Institute of Microbiology, Kiel University, 24118, Kiel, Germany.
The Department of Life Sciences & The National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel.
Nat Commun. 2019 Jun 13;10(1):2595. doi: 10.1038/s41467-019-10600-7.
Plasmid acquisition is an important mechanism of rapid adaptation and niche expansion in prokaryotes. Positive selection for plasmid-coded functions is a major driver of plasmid evolution, while plasmids that do not confer a selective advantage are considered costly and expected to go extinct. Yet, plasmids are ubiquitous in nature, and their persistence remains an evolutionary paradox. Here, we demonstrate that non-mobile plasmids persist over evolutionary timescales without selection for the plasmid function. Evolving a minimal plasmid encoding for antibiotics resistance in Escherichia coli, we discover that plasmid stability emerges in the absence of antibiotics and that plasmid loss is determined by transcription-replication conflicts. We further find that environmental conditions modulate these conflicts and plasmid persistence. Silencing the transcription of the resistance gene results in stable plasmids that become fixed in the population. Evolution of plasmid stability under non-selective conditions provides an evolutionary explanation for the ubiquity of plasmids in nature.
质粒获取是原核生物快速适应和生态位扩展的重要机制。质粒编码功能的正选择是质粒进化的主要驱动力，而不赋予选择优势的质粒被认为是昂贵的，预计会灭绝。然而，质粒在自然界中无处不在，它们的持续存在仍然是一个进化悖论。在这里，我们证明了非移动质粒在没有选择质粒功能的情况下能够在进化时间尺度上持续存在。在大肠杆菌中进化一个最小的编码抗生素抗性的质粒，我们发现质粒的稳定性在没有抗生素的情况下出现，而质粒的丢失是由转录-复制冲突决定的。我们进一步发现环境条件调节这些冲突和质粒的持续存在。沉默抗性基因的转录会导致稳定的质粒在种群中固定下来。在非选择性条件下，质粒稳定性的进化为质粒在自然界中的普遍性提供了一个进化解释。
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