Cell lengths in glucose-Casamino Acids medium at 34 and 39°C. Wild-type strain AB21 (A and B), dnaA (R432L) dnaX+ strain AB20 (C and D), and dnaA R432L dnaX(Ts) strain EGC23 (E and F) cells growing exponentially at 34°C (A, C, and E) and 39°C (B, D, and F) were observed by phase-contrast microscopy. The abscissa scale changes in panel F. The average cell lengths (in micrometers) of cells within the 1- to 8-μm range are indicated in each panel; parentheses contain 1 standard deviation.