Lysis

About: Lysis is a research topic. Over the lifetime, 6072 publications have been published within this topic receiving 216978 citations.

From Penicillin-Binding Proteins to the Lysis and Death of Bacteria: A 1979 View

Abstract: The mechanism by which interference with the biosynthesis of bacterial cell wall causes death and lysis of bacteria appears more complex than originally thought. In an earlier model of the mode of action of beta-lactams, it was assumed that, in the presence of the antibiotics, bacteria synthesize a mechanically weak (poorly cross-linked) cell wall that ruptured under the osmotic-mechanical pressure of the normally growing cytoplasmic mass. However, recent findings suggest a much more complex picture. Lysis and, in at least some bacteria, loss of viability as well, seem to be catalyzed by autolytic enzymes (murein hydrolases), the destructive activity of which is triggered in the beta-lactam-treated bacterium via a poorly understood mechanism. Furthermore, different species of bacteria respond quite differently to treatment with the same beta-lactam: some bacteria are both killed and lysed, others only lose viability, whereas still other species respond mainly by a reversible inhibition of growth (beta-lactam-tolerant bacteria). In addition, structurally different beta-lactams may cause quite different biochemical, morphological, and antibacterial effects, even within the same bacterial species. It is conceivable, therefore, that there is more than one mechanism for loss of viability and/or lysis. Most of the bacteria examined so far contain a number (four to eight) of different penicillin-binding proteins. Genetic and physiological evidence obtained in E. coli indicate that these proteins play essential roles in a variety of physiological functions, such as maintenance of structural integrity, shape, and cell division. Pneumococci with a suppressed autolytic system are resistant to he lytic (and, partially at least, to the bactericidal) effect of beta-lactams. Interference with cell wall synthesis seems to trigger autolysin activity by upsetting the cellular control of autolytic enzyme. It is suggested that the irreversible antimicrobial effect of beta-lactams may have an indirect mechanism in other bacteria as well.

Evidence for Specific Secretion Rather than Autolysis in the Release of Some Helicobacter pylori Proteins

Abstract: We investigated whether Helicobacter pylori cells actively secrete proteins such as the urease subunits UreA and UreB and the GroES and GroEL homologs HspA and HspB or whether these proteins were present in the extracellular compartment as a consequence of autolysis. Using a subcellular fractionation approach associated with quantitative Western blot analyses, we showed that the supernatant protein profiles were very different from those of the cell pellets, even for bacteria harvested in the late growth phase; this suggests that the release process is selective. A typical cytoplasmic protein, a β-galactosidase homolog, was found exclusively associated with the pellet of whole-cell extracts, and no traces were found in the supernatant. In contrast, UreA, UreB, HspA, and HspB were mostly found in the pellet but significant amounts were also present in the supernatant. HspA and UreB were released into the supernatant at the same rate throughout the growth phase (3%), whereas large portions of HspB and UreA were released during the stationary phase (over 30 and 20%, respectively) rather than during the early growth phase (20% and 6, respectively). The profiles of protein obtained after water extraction of the bacteria with those of the proteins naturally released within the liquid culture supernatants demonstrated that water extraction led to the release of a large amount of protein due to artifactual lysis. Our data support the conclusion that a specific and selective mechanism(s) is involved in the secretion of some H. pylori antigens. A programmed autolysis process does not seem to make a major contribution.