Department of Biology, Stanford University, Stanford, CA 94305.
Sarafan Chemistry, Engineering, and Medicine for Human Health Institute, Stanford University, Stanford, CA 94305.
Proc Natl Acad Sci U S A. 2024 Oct 8;121(41):e2406397121. doi: 10.1073/pnas.2406397121. Epub 2024 Oct 3.
In proliferating bacteria, growth rate is often assumed to be similar between daughter cells. However, most of our knowledge of cell growth derives from studies on symmetrically dividing bacteria. In many α-proteobacteria, asymmetric division is a normal part of the life cycle, with each division producing daughter cells with different sizes and fates. Here, we demonstrate that the functionally distinct swarmer and stalked daughter cells produced by the model α-proteobacterium can have different average growth rates under nutrient-replete conditions despite sharing an identical genome and environment. The discrepancy in growth rate is due to a growth slowdown associated with the cell cycle stage preceding DNA replication (the G1 phase), which initiates in the late predivisional mother cell before daughter cell separation. Both progenies experience a G1-associated growth slowdown, but the effect is more severe in swarmer cells because they have a longer G1 phase. Activity of SpoT, which produces the (p)ppGpp alarmone and extends the G1 phase, accentuates the cell cycle-dependent growth slowdown. Collectively, our data identify a coupling between cell growth, the G1 phase, and asymmetric division that may exploit for environmental adaptation through SpoT activity. This coupling differentially modulates the growth rate of functionally distinct daughter cells, thereby altering the relative abundance of ecologically important G1-specific traits within the population.
在增殖细菌中，子细胞之间的生长速度通常被认为是相似的。然而，我们对细胞生长的大部分了解都来自于对对称分裂细菌的研究。在许多α-变形菌中，不对称分裂是生命周期的正常组成部分，每次分裂都会产生大小和命运不同的子细胞。在这里，我们证明了模型α-变形菌 产生的功能不同的游动细胞和柄细胞在营养充足的条件下可以具有不同的平均生长速率，尽管它们共享相同的基因组和环境。生长速率的差异是由于与 DNA 复制前的细胞周期阶段（G1 期）相关的生长减慢引起的，该阶段在子细胞分离前的晚期预分裂母细胞中开始。两个后代都经历了与 G1 相关的生长减慢，但在游动细胞中更为严重，因为它们的 G1 期更长。产生（p）ppGpp 警报素并延长 G1 期的 SpoT 活性增强了细胞周期依赖性生长减慢。总的来说，我们的数据确定了细胞生长、G1 期和不对称分裂之间的耦合，通过 SpoT 活性，这种耦合可能会被利用来进行环境适应。这种耦合差异调节了功能不同的子细胞的生长速率，从而改变了种群中生态重要的 G1 特异性特征的相对丰度。
