Lysis of the cell membrane of Escherichia coli K12 by ionic detergents.
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Bacteriolysis↗
Biomedical subjects
C L Woldringh
Publications and source records attributed to C L Woldringh.
Effects of temperature inactivation of penicillin-binding protein 2 on envelope growth in Escherichia coli.
The transition from rod-shaped to spheroidal cells was studied in a temperature-sensitive strain (SP45) of Escherichia coli K12, carrying a mutation (pbpA) in the gene coding for penicillin-binding protein 2 (PBP-2). This transition imposed by the restrictive temperature was associated with reduction of peptidoglycan/surface area and of cellular osmotic stability. Addition of nalidixic acid (20 micrograms/ml) at the temperature shift from 30 to 42 degrees C resulted in lysis of some cells and appearance of spheroidal bulges along the cylinders in other cells, consistent with the hypothesis of envelope weakening due to inactivation of PBP-2.
Acyltransferases↗
Toporegulation of bacterial division according to the nucleoid occlusion model.
A model for the toporegulation of division in Escherichia coli is presented in which cell constriction is initiated by the combined action of a biochemical and a structural event. It is proposed that the biochemical event of termination of DNA replication causes a transient change in the pool of deoxyribonucleotides, which serves as a localized trigger that is converted to a diffusible, cytoplasmic activator of peptidoglycan synthesis. The second event involves the segregation of the nucleoids. Evidence is presented that the nucleoid suppresses the activity of peptidoglycan synthesis in its vicinity. It is proposed that active transcription/translation around the nucleoids produces a strong but short-range inhibitor which prohibits division (nucleoid occlusion). The combined effects of the locally produced termination-activator and of the diminished occlusion as a result of nucleoid segregation, guarantee that division is normally placed between the separated nucleoids. The model can explain the pattern of division-recovery of filaments, the majority of which constrict at sites which produce polar daughter cells containing two nucleoids. In addition, the model offers an explanation for the occurrence of mini-cells under a variety of conditions.
Cell Division↗
Visualizing multiple constrictions in spheroidal Escherichia coli cells.
An Escherichia coli cell grows by elongation and divides in a perpendicular plane. Alternating planes of successive divisions in three dimensions can only be ascertained when multiple constrictions exist simultaneously in large, spheroidal cells (with extended constriction process), if the division signals are enhanced. Large, spheroidal cells are obtained by a brief mecillinam treatment, and more frequent divisions are achieved by manipulating the rate of chromosome replication without affecting cell mass growth rate. Such a procedure has recently been performed by thymine-limitation of E. coli K12 strain CR34 (Zaritsky et al., Microbiology 145 (1999), 1052-1022). Enhancing the replication rate in cells with multi-forked replicating chromosomes (by addition of deoxyguanosine) shortens the intervals between successive terminations and thus triggers divisions more frequently. Monoclonal antibodies against FtsZ were used to visualize the rings of secondary constrictions, but apparent shortage of FtsZ to complete rings over wide cells allowed assembly of arcs only. The arcs observed were not parallel nor perpendicular; the tilted constriction planes are consistent with our 3-D 'nucleoid segregation'model for division under conditions which relieve the cylindrical constraint for nucleoid segregation by the bacillari peptidoglycan sacculus (Woldringh et al. , J. Bacteriol. 176 (1994) 6030-6038). The shortage in FtsZ may explain the longer time required to complete the division process in wide cells with long circumferences, observed during thymine step-up. Overexpression of fusion protein FtsZ-GFP on a multi-copy plasmid should circumvent the shortage.
Bacterial Proteins↗
Escherichia coli contains a DNA replication compartment in the cell center.
The active replication forks of E. coli B/r K cells growing with a doubling time of 210 min have been pulse-labeled with [(3)H] thymidine for 10 min. By electron-microscopic autoradiography the silver grains have been localized in the various length classes. From the known pattern of the DNA replication period in the cell cycle at slow growth and from the average position of grains per length class it was deduced that DNA replication starts in the cell center and that it remains there for a substantial part of the DNA replication period. This suggests the occurrence of a centrally located DNA replication compartment.
Autoradiography↗
Cellular localization of oriC during the cell cycle of Escherichia coli as analyzed by fluorescent in situ hybridization.
The origin of replication of Escherichia coli, oriC, has been labeled by fluorescent in situ hybridization (FISH). The E. coli K12 strain was grown under steady state conditions with a doubling time of 79 min at 28 degrees C. Under these growth conditions DNA replication starts in the previous cell cycle at -33 min. At birth cells possess two origins which are visible as two separated foci in fully labeled cells. The number of foci increased with cell length. The distance of foci from the nearest cell pole has been measured in various length classes. The data suggest: i) that the two most outwardly located foci keep a constant distance to the cell pole and they therefore move apart gradually in line with cell elongation; and ii) that at the initiation of DNA replication the labeled origins occur near the center of prospective daughter cells.
Cell Cycle↗
Physiological and geometrical conditions for cell division in Escherichia coli.
During recovery of division in filaments of a temperature-sensitive DNA replication mutant, DNA-less cells were formed with a broad variation in cell lengths. It is argued that segregated nucleoids are necessary to indicate the site of division and that, in their absence, the cell has no additional mechanism to locate the division site. A second condition for division is based on geometrical arguments: the cell must be able to reestablish its original surface to volume ratio or its diameter, either of which may decrease during elongation. Electron microscopy and auto-radiography of radio-labelled sacculi prepared from E. coli MC4100 lysA, cultured in glucose minimal medium, showed that these cells elongate at a constant diameter and double their rate of surface synthesis during the constriction period.
Cell Division↗