Genes for l-sorbose utilization in Escherichia coli

Area of Science:

• Microbiology
• Bacterial Genetics

Background:

• Escherichia coli laboratory strains (K12, B, C) are typically unable to metabolize L-sorbose.
• Wild strains exhibit variability in L-sorbose utilization, with some naturally using it and others mutating to do so.

Purpose of the Study:

• To genetically characterize L-sorbose utilization (sor+) in Escherichia coli.
• To identify the genes involved in L-sorbose metabolism and understand their regulation.
• To investigate methods for improving the efficiency of gene transfer related to L-sorbose utilization.

Main Methods:

• Genetic analysis of wild and laboratory strains of Escherichia coli.
• Transduction experiments to transfer L-sorbose utilization genes (sor+).
• Complementation tests to identify distinct genes involved in L-sorbose metabolism.
• Investigating the role of specific genes like phosphofructokinase (pfkA), phosphocarrier protein (ptsH), and phosphotransferase enzyme I (ptsI).

Main Results:

• Identified two key genes for L-sorbose utilization (sor+), cotransducible with metA.
• Established the gene order metA-ace-sor-pgi-mal.
• Demonstrated positive control of the K12 catabolite repressor protein over introduced sor+ genes.
• Showed that phosphofructokinase (pfkA), phosphocarrier protein (ptsH), and phosphotransferase enzyme I (ptsI) are essential for L-sorbose utilization.
• Observed that L-sorbose partially inhibits growth, reducing transduction frequency.
• Found that uridine, thymidine, and sorbitol counteract this inhibition and increase transduction frequency.

Conclusions:

• L-sorbose utilization in Escherichia coli involves specific genes regulated by the host's catabolite repression system.
• Key enzymes in glycolysis, including phosphofructokinase, are implicated in L-sorbose metabolism.
• Growth inhibition by L-sorbose can be overcome by specific compounds, facilitating genetic studies and strain improvement.