A cryptic melibiose transporter gene possessing a frameshift from Citrobacter freundii

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Wild-type Citrobacter freundii lacks the ability to metabolize melibiose as a primary carbon source.
• Melibiose utilization in bacteria is mediated by specific transporter proteins encoded by the melB gene.

Purpose of the Study:

• To clone and characterize the melibiose transporter gene (melB) from a Citrobacter freundii mutant capable of melibiose utilization.
• To engineer a functional melB gene and investigate the properties of the resulting melibiose transporter.

Main Methods:

• Cloning of the melB gene from a melibiose-utilizing C. freundii mutant.
• Site-directed mutagenesis to correct a frameshift mutation in the cloned melB gene.
• Analysis of cation coupling and amino acid sequence similarity of the functional MelB transporter.

Main Results:

• A cryptic melB gene was identified in the C. freundii mutant, containing a frameshift mutation.
• Site-directed mutagenesis successfully restored melB gene function, producing an active melibiose transporter.
• The C. freundii MelB transporter utilizes sodium (Na+) and proton (H+) as coupling cations and shows high sequence similarity to MelB proteins from Salmonella typhimurium and Escherichia coli.

Conclusions:

• The functional characterization of the C. freundii melibiose transporter (MelB) provides insights into bacterial sugar transport mechanisms.
• The cation coupling properties and phylogenetic relationships of MelB support evolutionary connections between bacterial species.
• Genetic engineering of the melB gene enables melibiose metabolism in C. freundii, with implications for microbial biotechnology.