A fourth Escherichia coli gene system with the potential to evolve beta-glucoside utilization

Area of Science:

• Microbial Genetics
• Evolutionary Biology
• Bacterial Metabolism

Background:

• Wild-type Escherichia coli K12 cannot metabolize beta-glucoside sugars like arbutin, salicin, or cellobiose.
• Previous studies identified mutations in the bgl and cel operons, and arbT locus, enabling utilization of these sugars.

Purpose of the Study:

• To investigate the potential for adaptive evolution within the genome of a single organism, specifically Escherichia coli K12.
• To identify novel genetic loci responsible for beta-glucoside utilization beyond known pathways.

Main Methods:

• Isolation and characterization of a novel mutant exhibiting utilization of salicin, arbutin, and cellobiose.
• Genetic analysis including cloning and hybridization studies to differentiate the new locus from known operons.
• Growth assays on minimal media and liquid cultures to assess utilization efficiency and identify potential limitations.

Main Results:

• A unique mutant was isolated from a strain lacking bgl and cel operons, indicating a novel genetic basis for sugar utilization.
• Further mutations enhanced growth on salicin and cellobiose, suggesting stepwise adaptive evolution.
• The newly identified gene system, designated the sac locus, was cloned and shown not to hybridize with bgl or cel probes.
• Mutants displayed specific induction levels in response to arbutin and salicin when assayed with a p-nitrophenyl-beta-D-glucoside substrate.

Conclusions:

• The sac locus represents a fourth distinct genetic system in E. coli K12 capable of evolving beta-glucoside utilization.
• This finding highlights the genome's capacity for adaptive evolution and the discovery of new metabolic pathways.