Ags1 is responsible for the strength of the primary septum structure needed during cell separation. (A) Ags1-depleted cells exclusively display asymmetrical cell separation and remain attached by their side. Arrow: normal straight separation; arrowhead: asymmetrical separation. Cells were grown in EMM+T+S for 8 h. The percentage of each cell separation was quantified. (B) WT cells separate gradually (top panels), whereas the Ags1-depleted cells suffer an immediate side-explosive separation. Cells were grown in EMM+T for 3 h and imaged. Asterisk, time spent for maximal new end curvature. Broken arrow: first separation step of symmetrical cell wall degradation. (C) Loss of Ags1 function promotes a side-explosive separation similar to that of Ags1 absence. mok1-664 cells were shifted to 37°C for 1 h and imaged. (D) The side-explosive cell separation (curved arrow) occurs instantly, in the interval between two image captures. Cells were grown as in A. (E) The side-explosive separation is caused by an abrupt primary septum tearing, which remains intact in the new poles for a long time. Cells from B were visualized by CW staining. Elapsed time is shown in seconds. Bars, 5 µm.