Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093.
US Department of Energy, Joint Genome Institute, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2022 Sep 13;119(37):e2110342119. doi: 10.1073/pnas.2110342119. Epub 2022 Sep 6.
To swim and navigate, motile bacteria synthesize a complex motility machinery involving flagella, motors, and a sensory system. A myriad of studies has elucidated the molecular processes involved, but less is known about the coordination of motility expression with cellular physiology: In , motility genes are strongly up-regulated in nutrient-poor conditions compared to nutrient-replete conditions; yet a quantitative link to cellular motility has not been developed. Here, we systematically investigated gene expression, swimming behavior, cell growth, and available proteomics data across a broad spectrum of exponential growth conditions. Our results suggest that cells up-regulate the expression of motility genes at slow growth to compensate for reduction in cell size, such that the number of flagella per cell is maintained across conditions. The observed four or five flagella per cell is the minimum number needed to keep the majority of cells motile. This simple regulatory objective allows cells to remain motile across a broad range of growth conditions, while keeping the biosynthetic and energetic demands to establish and drive the motility machinery at the minimum needed. Given the strong reduction in flagella synthesis resulting from cell size increases at fast growth, our findings also provide a different physiological perspective on bacterial cell size control: A larger cell size at fast growth is an efficient strategy to increase the allocation of cellular resources to the synthesis of those proteins required for biomass synthesis and growth, while maintaining processes such as motility that are only needed on a per-cell basis.
为了游泳和导航，运动细菌合成了一种复杂的运动机制，其中包括鞭毛、马达和感觉系统。大量的研究已经阐明了所涉及的分子过程，但对于运动表达与细胞生理学的协调知之甚少：在 中，与营养充足的条件相比，运动基因在营养匮乏的条件下被强烈上调；然而，尚未建立与细胞运动的定量联系。在这里，我们系统地研究了广泛的指数生长条件下的基因表达、游泳行为、细胞生长和可用蛋白质组学数据。我们的结果表明，细胞在生长缓慢时上调运动基因的表达，以补偿细胞体积的减少，从而使每个细胞的鞭毛数量在条件下保持不变。观察到的每个细胞四到五个鞭毛是使大多数细胞保持运动所必需的最小数量。这种简单的调节目标允许 细胞在广泛的生长条件下保持运动，同时将建立和驱动运动机制的生物合成和能量需求保持在最低水平。鉴于在快速生长时细胞大小增加导致鞭毛合成的强烈减少，我们的发现也为细菌细胞大小控制提供了一个不同的生理学视角：在快速生长时更大的细胞大小是一种有效的策略，可以增加细胞资源分配给生物量合成和生长所需的那些蛋白质的合成，同时维持仅按细胞为基础需要的运动等过程。
