Arginine catabolism by Treponema denticola

Area of Science:

• Microbiology
• Bacterial Metabolism
• Oral Microbiome

Background:

• Treponema denticola is an anaerobic bacterium found in the human mouth.
• It is known to ferment various substrates, including amino acids and glucose.
• Understanding its metabolic pathways is crucial for comprehending its role in the oral environment.

Purpose of the Study:

• To investigate the metabolic fate of L-arginine in Treponema denticola.
• To elucidate the specific enzymes and pathways involved in arginine utilization.
• To identify any unique metabolic characteristics of T. denticola compared to other bacteria using similar pathways.

Main Methods:

• Analysis of amino acid utilization and product formation by T. denticola cell suspensions.
• Radiotracer studies using L-[U-14C]ornithine to track metabolic conversions.
• Enzyme assays to detect arginine deiminase and ornithine carbamoyltransferase activities in cell extracts.

Main Results:

• Treponema denticola metabolized L-arginine to citrulline, ammonia (NH3), carbon dioxide (CO2), proline, and ornithine.
• L-citrulline was further metabolized to CO2, NH3, ornithine, and proline.
• Radioactive labeling confirmed the conversion of L-ornithine to proline, which was also excreted by growing cells.
• Enzyme assays detected arginine deiminase and ornithine carbamoyltransferase activities.
• Carbamoylphosphate dissimilation by cell extracts produced adenosine triphosphate (ATP).

Conclusions:

• Treponema denticola derives energy from L-arginine via the arginine deiminase pathway.
• A significant portion of the ornithine generated from L-arginine is converted to proline by T. denticola.
• This proline production represents a distinct metabolic feature of T. denticola within the context of arginine deiminase pathway utilization.