FzlA overproduction is toxic. (A) Representative phase-contrast time-lapse images of constricting cells that result in lethal division events due to FzlA overproduction. (B) Quantification of lethal divisions in the WT and ftsW**I* background comparing EV controls (WT: EG1644, n = 182 division events; ftsW**I*: EG3466, n = 145) and to fzlA overexpression (OE; WT: EG3637, n = 155; ftsW**I*: EG3467, n = 140). (C) Spot dilutions of WT or ftsW**I* strains harboring an EV control or fzlA variant overexpression construct, plated with 0.3% xylose (+Inducer) or 0.2% glucose (−Inducer). (D) Growth curves of WT or ftsW**I* strains harboring an EV control or fzlA-overexpression construct. Strains were pre-induced for 6 h with 0.3% xylose and induction continued with 0.3% xylose during the experiment. Points are the mean of three technical replicates at that timepoint, error bars are SEM. Shown is a representative replicate of a biological triplicate. (E) Phase-contrast time course of WT or ftsW**I* cells harboring an EV control or fzlA-overexpression construct. (F) Example phase-contrast images of cells after 20 h of FzlA overproduction in an ftsW**I* background. Arrow colors: green = very short cells, orange = one half of the constricted cell lysed, blue = cell chaining.