Department of Infection, Immunity and Inflammation, Institut Cochin, Inserm U1016, CNRS UMR8104, Université de Paris, 75014 Paris, France.
INSERM U1137, Université de Paris, 75018 Paris, France.
Nucleic Acids Res. 2022 Dec 9;50(22):12601-12620. doi: 10.1093/nar/gkac332.
Quick growth restart after upon encountering favourable environmental conditions is a major fitness contributor in natural environment. It is widely assumed that the time required to restart growth after nutritional upshift is determined by how long it takes for cells to synthesize enough ribosomes to produce the proteins required to reinitiate growth. Here we show that a reduction in the capacity to synthesize ribosomes by reducing number of ribosomal RNA (rRNA) operons (rrn) causes a longer transition from stationary phase to growth of Escherichia coli primarily due to high mortality rates. Cell death results from DNA replication blockage and massive DNA breakage at the sites of the remaining rrn operons that become overloaded with RNA polymerases (RNAPs). Mortality rates and growth restart duration can be reduced by preventing R-loop formation and improving DNA repair capacity. The same molecular mechanisms determine the duration of the recovery phase after ribosome-damaging stresses, such as antibiotics, exposure to bile salts or high temperature. Our study therefore suggests that a major function of rrn operon multiplicity is to ensure that individual rrn operons are not saturated by RNAPs, which can result in catastrophic chromosome replication failure and cell death during adaptation to environmental fluctuations.
在遇到有利的环境条件后快速重新开始生长是自然环境中主要的适应能力。人们普遍认为，在营养物质增加后重新开始生长所需的时间取决于细胞合成足够核糖体以产生重新开始生长所需的蛋白质所需的时间。在这里，我们表明，通过减少核糖体 RNA（rRNA）操纵子（rrn）的数量来降低核糖体合成能力，主要会导致大肠杆菌从静止期到生长的转变时间延长，这主要是由于高死亡率所致。细胞死亡是由于 DNA 复制受阻以及剩余 rrn 操纵子上的大量 DNA 断裂所致，这些操纵子因 RNA 聚合酶（RNAP）过载而变得超载。通过防止 R 环形成和提高 DNA 修复能力，可以降低死亡率和生长恢复持续时间。相同的分子机制决定了核糖体受损应激（例如抗生素、胆汁盐暴露或高温）后恢复阶段的持续时间。因此，我们的研究表明，rrn 操纵子多样性的主要功能是确保单个 rrn 操纵子不会被 RNAP 饱和，这可能导致在适应环境波动时灾难性的染色体复制失败和细胞死亡。
