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Mutants of Escherichia coli defective in penicillin-insensitive murein DD-endopeptidase
Abstract:
Two mutants of Escherichia coli that are deficient in the penicillin-insensitive DD-endopeptidase have been isolated. The strain JE10874 (mepA) has about 10%-20% of the residual activity and another strain, JE10368 (mepB) has 40%-50% of the activity found in the wild-type, parental strain, PA3092. The penicillin-insensitive endopeptidase is a periplasmic enzyme. Genetic mapping studies show that the mutation mepA is located close to aroC (50 min) and the other mutation, mepB, is very close to malE (91 min) on the chromosome. These mutants grow normally under a wide range of growth conditions; other phenotypic properties of the mutants are very similar to those of the parent strain. A double mutant (mepA mepB), and a triple mutant (mepA mepB dacB), deficient in both penicillin-insensitive and penicillin-sensitive endopeptidases, were constructed. Again, these mutants grew normally. We conclude that either the very low level of residual enzyme activity in the mutants is enough for their survival or that the penicillin-insensitive endopeptidase is not essential for survival under laboratory conditions.
Insights
Researchers isolated Escherichia coli mutants deficient in penicillin-insensitive DD-endopeptidase. These mutants, including double and triple mutants, exhibited normal growth, suggesting the enzyme is not essential for survival under laboratory conditions.
Area of Science:
- Microbiology
- Molecular Biology
- Enzymology
Background:
- Penicillin-insensitive DD-endopeptidase plays a role in bacterial cell wall metabolism.
- Understanding the function of this enzyme is crucial for bacterial survival studies.
Purpose of the Study:
- To investigate the essentiality of penicillin-insensitive DD-endopeptidase in Escherichia coli.
- To characterize mutants deficient in this specific enzyme.
Main Methods:
- Isolation and characterization of two Escherichia coli mutants (mepA and mepB) with reduced penicillin-insensitive DD-endopeptidase activity.
- Genetic mapping to determine the chromosomal locations of the mepA and mepB mutations.
- Construction and analysis of double (mepA mepB) and triple (mepA mepB dacB) mutants.
Main Results:
- The mepA mutant retained 10%-20% residual activity, while the mepB mutant had 40%-50% activity compared to the wild-type.
- The mepA mutation mapped near aroC (50 min) and mepB near malE (91 min).
- All generated mutants, including the double and triple mutants, displayed normal growth patterns and similar phenotypic properties to the parent strain.
Conclusions:
- The penicillin-insensitive DD-endopeptidase may not be essential for Escherichia coli survival under standard laboratory conditions.
- The residual enzyme activity in the isolated mutants might be sufficient for viability.
- Further research is needed to fully elucidate the enzyme's role in bacterial physiology.