Environmental pH impacts division assembly and cell size in Escherichia coli

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 key 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 machinery and activate division. Acidic environments lead to enrichment of FtsN at the septum and activation of division at a reduced cell length, while alkaline pH inhibits FtsN localization and suppress division activation. Altogether, our work reveals a previously unappreciated role for pH in bacterial cell size control.