Constriction Rate Modulation Can Drive Cell Size Control and Homeostasis in C. crescentus

Abstract

SummaryRod-shaped bacteria typically grow first via sporadic and dispersed elongation along their lateral walls and then via a combination of zonal elongation and constriction at the division site to form the poles of daughter cells. Although constriction comprises up to half of the cell cycle, its impact on cell size control and homeostasis has rarely been considered. To reveal the roles of cell elongation and constriction in bacterial size regulation during cell division, we captured the shape dynamics of Caulobacter crescentus with time-lapse structured illumination microscopy and used molecular markers as cell-cycle landmarks. We perturbed the constriction rate using a hyperconstriction mutant or fosfomycin ([(2R,3S)-3-methyloxiran-2-yl]phosphonic acid) inhibition. We report that the constriction rate contributes to both size control and homeostasis, by determining elongation during constriction and by compensating for variation in pre-constriction elongation on a single-cell basis.

Bacterial cell division at a glance

“…Moreover, the fully assembled divisome in C. crescentus can be held in an inactive state by SidA or DidA, small protein inhibitors of constriction that bind the late divisome proteins FtsW and/or FtsN upon DNA damage (Modell et al, 2011(Modell et al, , 2014. Mutations in FtsW or FtsI that bypass inhibition by SidA and DidA hyperactivate these PG synthases such that the cells constrict faster than wild type (Lambert et al, 2018;Lariviere et al, 2019;Modell et al, 2014). Similarly, hyperactivating mutations in the divisome proteins FtsL and FtsB were described in E. coli to cause premature initiation of constriction and/or cell shortening (Liu et al, 2015; Tsang and Bernhardt, 2015).…”

“…In that organism, an essential, direct binding partner of FtsZ called FzlA participates in activation of the downstream PG synthases (Goley et al, 2010;Lariviere et al, 2018Lariviere et al, , 2019) (see poster). Although fzlA is normally essential for division, hyper-activating mutations in ftsW and/or ftsI allow deletion of fzlA, indicating that the essential function of FzlA is to activate FtsWI (Lambert et al, 2018;Lariviere et al, 2019). Many of the proteins described in the E. coli activation pathway are present in C. crescentus; it is therefore likely that FzlA ultimately signals through FtsA, FtsK, FtsN and/or FtsQLB.…”

pH-dependent activation of cytokinesis modulates Escherichia coli cell size

“…Thus, the division proteins with domains in the periplasm are directly exposed to dynamic and potentially extreme environmental conditions-including changes in pH, osmolarity, and ionic strength-that may impact their ability to activate and complete cross wall synthesis. Differential activation of periplasmic components of the cell division machinery is sufficient to alter cell size at steady state: in E. coli and Caulobacter crescentus, gain-of-function mutations that affect the initiation or rate of septal cell wall synthesis consistently reduce size independent of changes to growth rate [18][19][20][21][22]. However, whether extracytoplasmic division proteins represent native integration points for environmental modulation of cell size remains unclear.…”

Environmental pH impacts division assembly and cell size inEscherichia coli

“…Exterior to the plasma membrane, these so-called ‘late’ division proteins are directly exposed to dynamic and potentially extreme environmental conditions—including changes in pH, osmolarity, and ionic strength—that may impact their ability to activate and complete cross wall synthesis [14,15]. Differential activation of the divisome has the potential to impact cell size homeostasis: hypermorphic mutants of E. coli and Caulobacter crescentus that affect the initiation or rate of septal cell wall synthesis are consistently short independent of changes to growth rate [16–20]. However, whether these represent native integration points for environmental modulation of cell size homeostasis remains unclear.…”