Membrane-murein attachment at the leading edge of the division septum: a second membrane-murein structure associated with morphogenesis of the gram-negative bacterial division septum

Abstract

Electron microscopy of plasmolyzed cells of Salmonella typhimurium revealed a continuous zone of membrane-murein attachment at the leading edge of the division septum at all stages of septal invagination. The membrane-murein attachment site had a characteristic ultrastructural appearance and remained as a bacterial birth scar at the new pole of each of the two daughter cells after cell separation. The continuous zone of membrane-murein attachment at the leading septal edge represents the second organelle based on a topologically ordered domain of membrane-murein adhesioh to be described at the site of cell division.Formation of the bacterial division septum occurs by the circumferential ingrowth of the cell envelope at the division site. In gram-negative bacteria, this formation requires the coordinate invagination of the three cell envelope layers, i.e., inner (cytoplasmic) membrane, murein, and outer membrane. The mechanism responsible for this topologically restricted differentiation is unknown.A new structure that appears at future division sites in gram-negative bacteria before the onset of septal invagination was recently described (4,8). The structure consists of two circumferential rings, the periseptal annuli, that flank the region of the cell envelope in which septal ingrowth will occur. Each annulus is a continuous zone where inner and outer membranes are closely apposed to the murein layer. It has been suggested (8) that the paired annuli define the periseptal domain and restrict essential elements of the division machinery to this location.In this paper, we describe a second division-related structure that is associated with ingrowth of the septum and that is also based on a topologically ordered domain of membrane-murein adhesion. The new structure consists of a continuous zone of membrane-murein attachment at the innermost edge of the nascent septum. After septal closure, the membrane-murein attachment site remains as a bacterial birth scar at the newly formed pole of each of the two daughter cells. MATERIALS AND METHODSSalmonella typhimurium SA534 (lkyD+), Rts34 [lkyD(Ts)] (5) and R71 (IkyD) (11) were grown in Proteose Peptone-beef extract medium (Difco Laboratories) containing 0.1 M NaCl to mid-exponential growth phase as previously described (5 30-min periods. The second method allows for a largely selective plasmolysis of the cell at the poles, while the first method results in general plasmolysis over the body of the cell and the poles (7,8,12).Unless otherwise noted, the final cell suspension was mixed with an equal volume of 4% glutaraldehyde in plasmolyzing buffer and immediately centrifuged, and the pellets were allowed to stand, without decanting of the supernatant solution, for 1.5 h at room temperature. The pellets were then washed three times with the plasmolyzing buffer, overlaid with 2% osmium tetroxide in the plasmolyzing buffer, and allowed to stand for an additional 1.5 h at room temperature. The cell pellets were then washed twice with distilled water, dehydrated through ethano...

Plasmolysis bays in Escherichia coli: are they related to development and positioning of division sites?

“…3B), may be explained by a strong interaction between the plasma membrane and the cell wall. Such a tight association was already emphasized by MacAlister et al (7,8), after visualization of plasmolyzed constriction sites in thin sections. They suggested the existence of a specific attachment at the leading edge of the constriction which persisted even after cell separation (1).…”

“…The existence of zones which are refractory to plasmolysis limits the space for development of lateral bays and displaces them toward the other cell half in the presence of a polar bay. Such zones of resistance do not seem to be supported by electron microscopic observations (7). Thin sections usually show small gaps between the plasma membrane and cell wall that are too small to be seen with the light microscope.…”

The dynamic interplay between a cell fate determinant and a lysozyme homolog drives the asymmetric division cycle of Caulobacter crescentus

“…SpmX might recognize a structural and/or chemical modification in the polar peptidoglycan layer that attracts it to the old cell pole, a view that is supported by our result that the muramidase domain is necessary and sufficient for the localization of SpmX to the stalked pole. Indeed, the cell division apparatus that directs the biosynthesis of the polar peptidoglycan during cytokinesis has been implicated in the deposition of a spatial mark at the newborn cell pole to cue protein localization (MacAlister et al 1987;Huitema et al 2006;Lam et al 2006). Like SpmX, the localization factor PodJ that recruits the PleC phosphatase to the newborn pole contains a motif thought to interact with peptidoglycan (Viollier et al 2002b;Hinz et al 2003).…”

Rate and topography of peptidoglycan synthesis during cell division in Escherichia coli: concept of a leading edge

“…MacAlister et al (14) showed, in thin sections of plasmolyzed S. typhimurium cells, the existence of a membrane-murein attachment site at the leading edge of the constriction site. The researchers suggested that at this innermost edge of the invaginated cell envelope, new septal murein is inserted.…”