This manifests as a negative correlation between the difference in cell elongation rate and the difference in interdivision intervals between two sisters (inserts JNK-IN-8 mouse Figure 3c and 3d; see also Additional File 13 – Figure S5). This is consistent with the interpretation that, during YgjD depletion, the timing of cell division remained coupled to a given cell size – and that the target cell size declined. The transition to decreased cell size is reminiscent of morphological changes that occur during the ‘stringent response’ [24, 25],
a stress adaptation program that is elicited when cells encounter amino-acid or carbon-starvation . The stringent response is induced by accumulation of the ‘alarmone’ guanosine tetra/penta phosphate ((p)ppGpp), e.g. in Angiogenesis inhibitor response to low concentrations of amino-acylated tRNAs . We thus wanted to investigate this possible link to (p)ppGpp signaling more closely, and asked whether the changes in cell homeostastis upon YgjD depletion are mediated through (p)ppGpp. Changes in cell size homeostastis are mediated through ppGpp We constructed a strain, TB84, that is deficient in (p)ppGpp synthesis ((p)pGpp0), due to deletions of relA and spoT [26, 27], and in which expression of ygjD was again under control
of Para. We followed growing microcolonies of TB84 as described above and found that the consequences of YgjD depletion were profoundly different: cell elongation rate decreased during filipin the YgjD depletion process as for the relA + spoT + strain TB80 (Figure 4a). In contrast to what we observed with this (p)ppGpp+ strain, the decrease p38 MAPK inhibitor in elongation rate was compensated for by an increase in the time interval between two divisions (Additional file 14 – movie 9, and Figure 4a). As a consequence, cell size at division was not reduced, and the final cell length of depleted (p)ppGpp0 cells (TB84) was on average twice that of depleted (p)ppGpp+ cells (TB80)
(Figure 4b). This is reminiscent of the elongated cells found in populations of cells depleted for YgjD by Handford and colleagues . Figure 4 The change in cell size homeostasis in response to YgjD depletion depends on (p)ppGpp. A) Changes in cell elongation rate and the interval between two divisions during YgjD depletion, for TB80 (ppGpp+) and TB84 (ppGpp0). For each strain, means and standard errors of three independent experiments are shown. In TB80, cell elongation rate starts to decrease after generation 3, and cells divide before they double in size. In TB84, cell division occurs close to the moment of cell size doubling (the means are close to the contour line of constant cell size). B) Change of mean cell size during YgjD depletion, for and TB80 (ppGpp+) and TB84 (ppGpp-). In TB80, cell size starts to decrease after generation 3, as a consequence of cell division that occurs before cells double in size (see panel A).