The morphogenetic MreBCD proteins of Escherichia coli form an essential membrane‐bound complex

Abstract

SummaryMreB proteins of Escherichia coli , Bacillus subtilis and Caulobacter crescentus form actin-like cables lying beneath the cell surface. The cables are required to guide longitudinal cell wall synthesis and their absence leads to merodiploid spherical and inflated cells prone to cell lysis. In B. subtilis and C. crescentus , the mreB gene is essential. However, in E. coli , mreB was inferred not to be essential. Using a tight, conditional gene depletion system, we systematically investigated whether the E. coli mreBCD -encoded components were essential. We found that cells depleted of mreBCD became spherical, enlarged and finally lysed. Depletion of each mre gene separately conferred similar gross changes in cell morphology and viability. Thus, the three proteins encoded by mre-BCD are all essential and function in the same morphogenetic pathway. Interestingly, the presence of a multicopy plasmid carrying the ftsQAZ genes suppressed the lethality of deletions in the mre operon. Using GFP and cell fractionation methods, we showed that the MreC and MreD proteins were associated with the cell membrane. Using a bacterial two-hybrid system, we found that MreC interacted with both MreB and MreD. In contrast, MreB and MreD did not interact in this assay. Thus, we conclude that the E. coli Mre-BCD form an essential membrane-bound complex. Curiously, MreB did not form cables in cell depleted for MreC, MreD or RodA, indicating a mutual interdependency between MreB filament morphology and cell shape. Based on these and other observations we propose a model in which the membrane-associated MreBCD complex directs longitudinal cell wall synthesis in a process essential to maintain cell morphology.

NblR Is a Novel One-Component Response Regulator in the CyanobacteriumSynechococcus elongatusPCC 7942

“…In E. coli, MreC has a transmembrane domain, it localizes to the inner membrane, and it is likely that the C-terminal region faces the periplasmic side. 31) Since there is as yet no information on the function of MreC in S. elongatus, the functional aspect of the interaction between NblR and MreC remains unclear. There is possible involvement of cell division signals in the regulation of NblR.…”

Getting into shape: How do rod-like bacteria control their geometry?

“…The orientation of the MreB filaments with respect to the cell envelope, in turn, could be caused by the filament-intrinsic curvature and twist in combination with a curved surface of the cylindrical cell envelope (Wang and Wingreen 2013;Andrews and Arkin 2007). Linking cell-wall synthesis to MreB filaments is very interesting from a physics perspective: multiple independent studies have suggested that MreB filaments assume on average macroscopic lengths of few 100 nm (Olshausen et al 2013;Reimold et al 2013;Kruse et al 2004;Jones et al 2001). The mechanical stiffness of these filaments (Wang et al 2010) could facilitate the macroscopic organization of the cell-wall synthesis machinery and might thus provide a key ingredient for a robust cell-shape feedback mechanism (see discussion below).…”

A widespread family of bacterial cell wall assembly proteins

“…MreB is essential for viability in many bacteria, and its depletion induces severe morphological defects (Jones et al, 2001;Figge et al, 2004;Kruse et al, 2005;Slovak et al, 2005;Hu et al, 2007). Many Gram-positive bacteria have more than one MreB isoform.…”