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A pH-conditional mutant of Escherichia coli.
Summary
Researchers identified a pH-conditional mutant in Escherichia coli, affecting beta-galactosidase activity. This enzyme is crucial for maintaining intracellular pH, especially under energy-dependent conditions.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Escherichia coli mutants were isolated exhibiting conditional growth on lactose based on pH.
- A specific mutant demonstrated impaired growth at pH 8.1 compared to pH 7.0.
- This phenotype mapped to the Z region of the lactose operon.
Purpose of the Study:
- To analyze the genetic basis of pH-conditional growth in Escherichia coli mutants.
- To investigate the role of beta-galactosidase in maintaining intracellular pH.
- To utilize a pH-conditional beta-galactosidase as a probe for intracellular pH.
Main Methods:
- Isolation and genetic mapping of pH-conditional mutants in Escherichia coli.
- Enzyme assays of beta-galactosidase activity in toluenized cells and purified enzyme.
- In vivo measurement of intracellular pH using the pH-conditional beta-galactosidase probe.
Main Results:
- Mutant beta-galactosidase exhibited significantly reduced activity at pH 8.0 compared to pH 7.0.
- Purified mutant enzyme showed pH-conditional activity, unlike the wild-type enzyme.
- Intracellular pH was maintained at approximately 7.8-8.0 across an external pH range of 5.9-7.8.
Conclusions:
- A pH-conditional mutant of beta-galactosidase was identified, impacting its enzymatic activity.
- Beta-galactosidase is essential for maintaining intracellular pH in an energy-dependent manner.
- pH-conditional mutants in cytoplasmic gene products can be recovered, unlike those in surface elements for non-energy-dependent phenotypes.