Understanding Cell Size Homeostasis and Phenotypic Switching Dynamics during Bacterial Filamentation

Colonies of bacteria undergoing filamentation present a noticeable phenotypic diversity in terms of their size and yet homeostasis is achieved. While the mechanism for achieving size homeostasis at a normal size scale is clear, the following questions remain in the context of filamentation. How do filamentous strains achieve size homeostasis? What is the dynamics underlying phenotypic switching? To answer these questions, we have modeled the bacterial growth and division processes during filamentation and performed analyses of experimental phenotypic lineage trees. Our model reveals how making compatible the observed adder-like correlations at the collective level and sizer properties at the individual cell level. We further show that size homeostasis is independent on the division pattern (i.e. what septa are eventually selected for cell cleavage in filamentous cells). Also, our analyses of lineage trees combined with mathematical models suggest that changes in the phenotypic composition of colonies mainly derive from a switch of the growth/division mode. Altogether, our work sheds light on the dynamics of filamentation and helps to understand the transition from a regular to a filamentous phenotype.