Cell size is a complex trait, derived from both genetic and environmental factors. Environmental determinants of bacterial cell size identified to date primarily target assembly of cytosolic components of the cell division machinery. Whether certain environmental cues also impact cell size through changes in the assembly or activity of extracytoplasmic division proteins remains an open question. Here, we identify extracellular pH as a modulator of cell division and a significant determinant of cell size across evolutionarily distant bacterial species. In the Gram-negative model organism Escherichia coli, our data indicate environmental pH impacts the length at which cells divide by altering the ability of the terminal cell division protein FtsN to localize to the cytokinetic ring where it activates division. Acidic environments lead to enrichment of FtsN at the septum and activation of division at a reduced cell length. Alkaline pH inhibits FtsN localization and suppresses division activation. Altogether, our work reveals a previously unappreciated role for pH in bacterial cell size control.

细胞大小是一个复杂的特征，源于遗传和环境因素。迄今为止确定的细菌细胞大小的环境决定因素主要针对细胞分裂机制的胞质组分的组装。某些环境线索是否还会通过胞浆外分裂蛋白的装配或活性变化来影响细胞大小仍然是一个悬而未决的问题。在这里，我们将细胞外pH值确定为细胞分裂的调节剂，并且是跨进化距离远的细菌物种的细胞大小的重要决定因素。在革兰氏阴性模型生物中，大肠杆菌，我们的数据表明环境pH通过改变末端细胞分裂蛋白FtsN定位于其激活分裂的细胞动力学环的能力，影响细胞分裂的长度。酸性环境会导致FtsN在隔膜处富集，并在细胞长度减少的情况下激活分裂。碱性pH抑制FtsN定位并抑制分裂活化。总而言之，我们的工作揭示了pH在细菌细胞大小控制中的前所未有的作用。