Some Studies of Bacterial Lysis and of the Bacterial Cell-Wall

Stern, Harold (1953) Some Studies of Bacterial Lysis and of the Bacterial Cell-Wall. PhD thesis, University of Glasgow.

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Investigations involving the use of the electron microscope have been carried out of the structural changes involved in bacterial autolysis, of the action on bacteria of a cationic detergent (cetyl-trimethyl-ammonium bromide), of the structure of the bacterial cell-wall and of the part played by the bacterial cell-wall in cell division. Spontaneous autolysis was studied in Staph, aureus and in B. subtilis, using both the intact cells and the isolated cell-walls. In both organisms the earliest visible change is a retraction of the cytoplasm from the cell-wall and this is associated with a change to the Gram-negative state. In the case of Staph, aureus this is followed by a slow, irregular disintegration of the cytoplasm within the cell-wall which also undergoes a slow, irregular disintegration but remains undisrupted until a relatively late stage. In B. subtilis the rate of autolysis is very much more rapid and this is due mainly to the early rupture of the cell-wall allowing rapid evacuation and dispersal of the cytoplasm; the cell-wall, itself, also undergoes a more rapid and uniform disintegration than the cell-wall of Staph, aureus. It is suggested that the loss of Gram-positivity during spontaneous autolysis is due not to enzymic activity but to the disruption of cytoplas-mic-cell-wall contact, the latter being associated with loss of soluble cytoplasmic constituents. Certain conditions (cell concentration, age of cells, washing of the cells, pH and temperature) influencing the rate of autolysis of Staph. aureus have also been studied. The action of CTAB on Staph, aureus and B. subtilis. again using both intact cells and isolated cell-walls for the investigation, has been found to follow stoichiometric proportions and to vary with the cell to detergent weight ratio. A high ratio results in a marked stimulation of autolytic disintegration of the cell. A low ratio results in cell fixation. Intermediate ratios cause stripping of the cell-wall but the cytoplasmic body, contrasted and Gram-negative, undergoes no further disintegration. From these results together with a comparison of the effects on autolysis of treatment of the bacterial cell with CTAB and with lipoid solvents an hypothesis has been formulated that detergents cause splitting of lipoprotein complexes throughout the cell: where the concentration of the detergent is relatively low this allows an acceleration of normal autolysis; with higher concentrations of detergent protein denaturation predominates and is responsible for inactivation of autolytic enzymes, cell-wall stripping and cell fixation. The quantitative results obtained show that the active unit of CTAB in producing the above effects is the free ion and not the micelle. The investigation of the intimate structure of the cell-wall of Staph. aureus tends to support the view that the cell-wall of this organism contains a protein, fibrous network. The cell-wall of B. subtilis. on the other hand, seems to consist of a mosaic of small, circular or oval units. The stages of bacterial cell division have been followed by examinations of the isolated cell-walls of Staph. aureus, Strept. faecalis and B. subtilis. In all three organisms a transverse cell-wall septum is formed which originates in and grows centripetally from the cell-wall. The cell-wall septum splits into two layers and division is completed by constriction of the cell-wall through the line of the double septum. Cell-wall septum formation and cell-wall constriction appear to be dissociable phenomena. A cytoplasmic membrane, forming transverse septa before the formation of the cell-wall septum, has been demonstrated in Strept. faecalis.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Microbiology, Cellular biology
Date of Award: 1953
Depositing User: Enlighten Team
Unique ID: glathesis:1953-79103
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 31 Mar 2020 09:09
Last Modified: 31 Mar 2020 09:09

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