S. aureus clpX cells grown at 30°C display aberrant septum ingrowth and initiate daughter cell separation prior to septum closure.
TEM (left panels) and SEM (right panel) images of SA564 wild-type (A) or clpX cells (B-F) grown in TSB to mid-exponential phase at 30°C. Images show characteristic morphologies of SA564 wild-type or clpX cells at 30°C as determined from at least three biological replicates. clpX cells displaying the normal coccoid morphology (B); the typical appearance of lysed clpX cells (C); clpX cells with non-divided cytoplasma displaying premature splitting of daughter cells (D); clpX cells displaying asymmetrical septum ingrowth, (E); clpX cells displaying mesosome-like structrues at the septal site (F). White arrows point to the intact peripheral cell wall at the site of septum that is typical for wild-type cells with unclosed septa, while black arrows point to signs of daughter cell splitting initiating from the peripheral wall in cells with closed division septa. Asterisk mark clpX cells that despite displaying an incomplete septum show signs of daughter cell splitting initiating from the peripheral wall. The displayed morphological changes are typical for clpX cells also in other S. aureus strain backgrounds tested (8325–4, and JE2). Scale bar, 0.2 μm.