Two genes affecting glucarate utilization in Escherichia coli K12

Area of Science:

• Microbial physiology and genetics
• Bacterial transport systems
• Metabolic pathways in Escherichia coli

Background:

• Escherichia coli K12 possesses mechanisms for nutrient uptake and metabolism.
• D-Glucarate is a compound that can potentially be utilized by bacteria.
• Understanding substrate transport is crucial for comprehending bacterial metabolic capabilities.

Purpose of the Study:

• To characterize the inducible D-glucarate transport system in Escherichia coli K12.
• To identify genetic determinants involved in D-glucarate uptake and metabolism.
• To investigate the relationship between D-glucarate transport and other metabolic functions.

Main Methods:

• Characterization of D-glucarate uptake kinetics (apparent rate and Km).
• Induction studies using different growth substrates (glucarate, glycollate).
• Competitive inhibition assays with galactarate.
• Isolation and genetic mapping of mutations affecting D-glucarate utilization (garA, garB, tonA).

Main Results:

• D-Glucarate is transported via an inducible system with an apparent Km of 16 μM and a rate of 7-15 nmol min-1 (mg dry mass)-1.
• Uptake is induced by growth on glucarate or glycollate.
• Galactarate competes for the same uptake system.
• A mutation (garA) impairs D-glucarate transport, glucarate dehydratase activity, and growth on glucarate/galactarate, mapping at min 16.
• Another mutation, likely a deletion of garB and tonA at min 3.5, shows an indistinguishable phenotype.

Conclusions:

• Escherichia coli K12 employs a specific, inducible transport system for D-glucarate.
• The garA gene is essential for both D-glucarate transport and its subsequent metabolism.
• The identified mutations provide insights into the genetic regulation of D-glucarate utilization in E. coli.