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Alteration of Escherichia coli murein during amino acid starvation
Abstract:
We have studied the mechanisms by which amino acid starvation of Escherichia coli induces resistance against the lytic and bactericidal effects of penicillin. Starvation of E. coli strain W7 of the amino acids lysine or methionine resulted in the rapid development of resistance to autolytic cell wall degradation, which may be effectively triggered in growing bacteria by a number of chemical or physical treatments. The mechanism of this effect in the amino acid-starved cells involved the production of a murein relatively resistant to the hydrolytic action of crude murein hydrolase extracts prepared from normally growing E. coli. Resistance to the autolysins was not due to the covalently linked lipoprotein. Resistance to murein hydrolase developed most rapidly and most extensively in the portion of cell wall synthesized after the onset of amino acid starvation. Lysozymes digests of the autolysin-resistant murein synthesized during the first 10 min of lysine starvation yielded (in addition to the characteristic degradation products) a high-molecular-weight material that was absent from the lysozyme-digests of control cell wall preparations. It is proposed that inhibition of protein synthesis causes a rapid modification of murein structure at the cell wall growth zone in such a manner that attachment of murein hydrolase molecules is inhibited. The mechanism may involve some aspects of the relaxed control system since protection against penicillin-induced lysis developed much slower in amino acid-starved relaxed controlled (relA) cells than in isogenic stringently controlled (relA+) bacteria.
Insights
Amino acid starvation in Escherichia coli triggers penicillin resistance by altering cell wall murein structure, making it resistant to degradation. This resistance is linked to inhibited protein synthesis and may involve the relaxed control system.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Penicillin induces bacterial lysis by inhibiting cell wall synthesis.
- Amino acid starvation is known to affect bacterial physiology and stress responses.
- Escherichia coli possesses autolytic enzymes that degrade its cell wall.
Purpose of the Study:
- To investigate the mechanisms by which amino acid starvation confers resistance to penicillin.
- To elucidate the role of cell wall structure and autolysins in this resistance phenomenon.
Main Methods:
- Inducing amino acid starvation (lysine or methionine) in Escherichia coli.
- Assessing resistance to penicillin-induced lysis and autolytic degradation.
- Analyzing murein structure and its susceptibility to murein hydrolase and lysozyme.
- Comparing resistance development in stringent (relA+) and relaxed (relA) control strains.
Main Results:
- Amino acid starvation rapidly induced resistance to penicillin lysis and autolytic degradation.
- Starved cells produced murein resistant to hydrolysis by E. coli murein hydrolase.
- Resistance was most pronounced in newly synthesized cell wall portions.
- A high-molecular-weight material was observed in lysozyme digests of resistant murein.
- Resistance developed slower in relaxed control (relA) cells compared to stringent control (relA+) cells.
Conclusions:
- Inhibition of protein synthesis during amino acid starvation modifies murein structure, preventing murein hydrolase attachment and conferring penicillin resistance.
- This resistance mechanism is associated with changes in the cell wall growth zone.
- The relaxed control system influences the rate of resistance development.