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Lactose metabolism in Erwinia chrysanthemi
Journal of Bacteriology
|April 1, 1985
Summary
Wild-type Erwinia chrysanthemi cannot grow on lactose, but spontaneous mutations enable lactose utilization. These mutations activate a lactose transport system (lmrT) and often a beta-galactosidase (lacZ or lacB).
Area of Science:
- Microbiology
- Bacterial Genetics
- Molecular Biology
Background:
- Wild-type Erwinia chrysanthemi, a phytopathogenic bacterium, lacks the ability to utilize lactose as a carbon source despite possessing beta-galactosidase activity.
- Spontaneous lactose-fermenting (Lac+) derivatives can be isolated, indicating genetic mechanisms for lactose utilization exist.
Purpose of the Study:
- To investigate the genetic basis of lactose utilization in Erwinia chrysanthemi.
- To identify and characterize the genes involved in lactose transport and beta-galactosidase activity.
- To understand the regulatory mechanisms governing lactose metabolism.
Main Methods:
- Isolation and characterization of spontaneous Lac+ derivatives.
- Cloning of the lmrT, lacZ, and lacI genes using an RP4::miniMu vector.
- Complementation studies in Lac- Escherichia coli strains.
- Mutagenesis to isolate structural mutants affecting lactose utilization.
Main Results:
- Lac+ derivatives possess a constitutive lactose transport system (lmrT gene) and an inducible beta-galactosidase (lacZ or lacB).
- The lmrT gene mediates the uptake of lactose and other sugars (melibiose, raffinose, galactose).
- Two beta-galactosidase genes (lacZ and lacB) were identified with distinct substrate affinities and inhibitor sensitivities.
- Cloning and expression of lmrT, lacZ, and lacI in E. coli confirmed their function and suggested lmrT is unlinked to lacZ/lacB.
- Mutations affecting lmrT or lacZ/lacB regulation and structure were identified.
Conclusions:
- Erwinia chrysanthemi can acquire lactose utilization capabilities through mutations affecting a lactose transport system (lmrT) and beta-galactosidase expression (lacZ/lacB).
- The identified genes and their regulatory elements provide insights into the genetic control of carbohydrate metabolism in this bacterium.
- The lacZ mutants, retaining low beta-galactosidase activity from lacB, are suitable for constructing gene fusions with E. coli lac genes.