Morphogenesis of the bacterial division septum: a new class of septation-defective mutants.

The lipoprotein content of the outer-membrane medium vesicles, which are released from Escherichia coli during normal growth, was compared to the lipoprotein content of the corresponding cellular outer membranes.It was found that the medium vesicles contained only 35% free lipoprotein and almost none of the bound lipoprotein when compared with cellular outer membranes. Medium vesicles also had reduced amounts of protein 11* and a protein V ( M , = 16000), while they contained large amounts of pore-forming proteins I and 1amB.A mechanism is proposed in which outer membrane vesicles are formed when the outer membrane expands faster than the underlying peptidoglycan layer. The lack or enrichment of individual proteins in medium vesicles may be determined by their interactions with the peptidoglycan-bound lipoprotein complex.The cell wall of gram-negative bacteria consists of a peptidoglycan layer and an outer membrane. These two layers are linked covalently via the bound form of the outer membrane lipoprotein [I -31.The lipoprotein is the most abundant protein of Escherichiu coli and many other gram-negative bacteria; there are of the order of 40000 such linkages per pm2 of bacterial cell surface, implying that the distance between neighbouring covalent murein-outer membrane connections averages S nm, which is less than a single membrane thickness [I].Despite this intimate and covalent contact between the outer membrane and the peptidoglycan layer, E. coli and other gram-negative bacteria release a significant portion of their outer membrane into the medium in the form of membrane vesicles during normal growth [4-81.Such vesicles have been observed under the electron microscope as outer-membrane 'blebs' that are released from the cell during the initial stages of septation [9,10]. Release of these vesicles is enhanced when protein synthesis is slowed down, for instance by growing a lysine auxotroph under lysine-limiting conditions or by growing E. coli in the presence of chloramphenicol [I 1,121. Adsorption of phage T4 to E. coli also results in a more pronounced release of outer-membrane vesicles into the medium [6,13].Extensive bleb formation has also been observed when a lipoprotein-lacking mutant was grown under conditions of magnesium starvation [14,15], while a mutant lacking the ompA protein a5 well as the lipoprotein showed extensive blebbing even in the presence of normal magnesium concentrations [16]. Comparable observations have been made in Salmonella typhimurium lkyD mutants which have a decreased amount of murein-bound lipoprotein [17-191. We have previously considered the possibility that, given the high average density of covalent lipoprotein-murein linkages in normal E. coli, outer-membrane vesicles may well be derived from envelope areas which are relatively poor in lipoprotein [4] ; the fact that lipoprotein-lacking mutants h z y m e . Lysozyme (EC 3.2.1.17) release considerably more outer membrane material than do normal cells supports this hypothesis.If the lack of (bound) lipoprotein in cert...

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“…Lysozyme (EC 3.2.1. 17) release considerably more outer membrane material than do normal cells supports this hypothesis.…”

supporting

confidence: 73%

Outer-Membrane Vesicles Released by Normally Growing Escherichia coli Contain Very Little Lipoprotein

1981

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“…The phenotype of cells of E. coli TOE27 [cha(Ts)] grown at 42°C was similar in several respects to that described previously for IkyD mutants of S. typhimurium (16,17). In both cases cells grown in the presence of 100 mM NaCl formed chains of four to six cells ( Fig.…”

Section: Resultssupporting

confidence: 50%

“…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.…”

mentioning

confidence: 99%

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

Chakraborti¹,

Ishidate²,

Cook³

et al. 1986

J Bacteriol

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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.

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“…By analogy with DD-transpeptidases, the putative (L)-m-A,pm:lipoprotein transpeptidase may catalyze nucleopbilie displacement of' the (i)-m-A~pm-D-ala peptide bond to form an acyl--cnzyme which employs the lipoprotein as an acceptor. In mutants of E. coli and Sahnonella typhimur/um with decreased levels of murein-bound lipoprotein, the outer membrane fails to invaginate with the murein layer during septation [11,12]. However, a mutant of t7,, toll that lacks the lipoprotein grows and divides normally; the abnormally leaky outer membrane of this mutant suggests the lipoprotein helps maintain the integrity of the cell wall [13].…”

Section: Metabolism and Physiology Of Ld-peptidesmentioning

confidence: 99%

Coordinate regulation of murein peptidase activity and AmpC β‐lactamase synthesis in Escherichia coli

Bishop¹,

Weiner²

1992

FEBS Letters

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In the periplasmic space of F.sche~'ichia coil, the (L)-m-A,pm-(D)-m-A,pm pcptid¢, the lipoprotein, and the AmpC fl-lactamas¢ are controlled by growth rate. To explain this coordinate regulation, it is proposed that the AmpC protein functions as an LD-endopeptidase in addition to its known function as a fl-lactamas¢. As LD-peptides, vo-peptides and fl-lactams are structurally similar, to-peptidases may belong to the larger family of DD-peptidases and serine ~-lactamases. In contrast to K coll. many related bacteria possess an inducible AmpC protein. Several gene systems necessary for AmpC induction are known to affect various aspects of peptidoglyean metabolism, It is proposed that AmpC induction ¢o=urs indirectly via a recyclabl¢ e¢ll wall pcptid¢.

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Morphogenesis of the bacterial division septum: a new class of septation-defective mutants.

Cited by 58 publications

References 11 publications

Outer-Membrane Vesicles Released by Normally Growing Escherichia coli Contain Very Little Lipoprotein

Outer-Membrane Vesicles Released by Normally Growing Escherichia coli Contain Very Little Lipoprotein

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

Coordinate regulation of murein peptidase activity and AmpC β‐lactamase synthesis in Escherichia coli

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