Accumulation of a murein-membrane attachment site fraction when cell division is blocked in lkyD and cha mutants of Salmonella typhimurium and Escherichia coli

Abstract

Membrane fractionation studies were performed on Salmonella typhimurium lkyD(Ts) and E. coli cha (Ts) mutants that appeared to be blocked at a late stage of the cell division cycle. In both cases growth of the mutant strains at nonpermissive temperatures was associated with accumulation of a characteristic cell envelope fraction (fraction OML) that contained inner membrane, murein, and outer membrane components. The isolated fraction corresponded in composition and buoyant density to a fraction from wild-type strains that had previously been suggested (M. H. Bayer, G. P. Costello, and M. E. Bayer, J. Bacteriol. 149:758-767, 1982; K. Ishidate, E. S. Creeger, J. Zrike, S. Deb, B. Glauner, T. J. MacAlister, and L. I. Rothfield, J. Biol. Chem. 261:428 443, 1986) to contain adhesion sites between inner membrane, murein, and outer membrane. The accumulation of OML in LkyD-and Cha-cells was prevented by treatments that blocked DNA synthesis. The effects of interference with DNA synthesis did not appear to involve the SOS response.The cell envelopes of gram-negative bacteria are composed of three morphologically distinct layers: cytoplasmic (inner) membrane, murein, and outer membrane (8). Electron microscopy of cells that have been plasmolyzed by exposure to hypertonic solutions has revealed zones of adhesion between the three layers at numerous locations along the body of the cell (1). At sites of cell division, the murein-membrane adhesion zones are organized into two concentric rings, the periseptal annuli, that flank the site of septal ingrowth (13). It is not known whether all the adhesion zones of the cell are related to these division-related structures or whether the cell envelope contains several different types of murein-membrane attachments.The isolation of a cell envelope fraction (fraction OML) that appears to contain attachments between inner membrane, murein, and outer membrane has been described (2, 9), but it has not been established whether the OML fraction includes the division-related attachment sites. It is assumed that the OML fraction contains membrane-murein adhesion sites together with flanking regions of inner membrane and outer membrane-murein. In this report we describe changes in the cell envelope fractionation patterns of two thermosensitive cell division mutants of Salmonella typhimurium and Escherichia coli that suggest a relationship between the isolated adhesion zone fraction OML and the division process.The two mutations, lkyD (17) and cha (4), both appear to affect a late stage in the division process. In each case the mutation is associated with an apparent defect in outer membrane invagination during septum formation. Growth at elevated temperatures results in the formation of septal crosswalls that contain only the murein and inner membrane components of the normal septum, leading to the formation of chains of cells that are held together by bridges of outer membrane (17; K.

Envelope Control of Outer Membrane Vesicle Production in Gram-Negative Bacteria

“…There appears to be a general correspondence of mutations in proteins involved in cell division and large circular structures emanating from the septum [55, 80, 81]. Although these structures have been labeled as “OMVs,” their size and site of budding are not what we typically see for OMVs produced by wild-type Gram-negative bacteria.…”

“…Besides its role in envelope stability, the Tol–Pal complex has been shown to aid in OM invagination during the constriction phase of cell division. , There appears to be a general correspondence of mutations in proteins involved in cell division and large circular structures emanating from the septum. ,, Although these structures have been labeled as “OMVs”, their size and site of budding are not what we typically see for OMVs produced by wild-type Gram-negative bacteria. Consequently, defining how Pal plays potentially separate roles in cell division and OMV production provides a challenge in the field.…”

Biosynthesis of a membrane adhesion zone fraction throughout the cell cycle of Escherichia coli

“…It was previously shown that the OML fraction accumulates to high levels in certain cell division mutants of E. coli and Salmonella typhimurium (cha and lkyD, respectively) that are blocked at a late stage of the division process (5 On the other hand, studies of the development of periseptal annuli have shown that new annuli are generated early in the division cycle (6). The annuli appear to continue their growth around the cylinder during much of the remainder of the cycle, during and after displacement to their final locations within the cell (6,7).…”