Arginine metabolism in lactic streptococci

Area of Science:

• Microbiology
• Biochemistry
• Metabolic Pathways

Background:

• Streptococcus lactis metabolizes arginine through the arginine deiminase pathway, yielding ornithine, ammonia, carbon dioxide, and ATP.
• Enzyme activity within this pathway is regulated by growth conditions and nutrient availability.

Purpose of the Study:

• To investigate the regulation of the arginine deiminase pathway in Streptococcus lactis under different growth conditions.
• To compare arginine metabolism capabilities between Streptococcus lactis and Streptococcus cremoris.

Main Methods:

• Enzyme activity assays (arginine deiminase, ornithine transcarbamylase, carbamate kinase) were performed on S. lactis strains grown on various sugars (glucose, lactose, galactose).
• Continuous and batch cultures were used to study arginine metabolism regulation in response to nutrient availability.
• S. cremoris strains were analyzed for the presence of key enzymes in the arginine deiminase pathway.

Main Results:

• Arginine deiminase and ornithine transcarbamylase activities were significantly higher in galactose-grown S. lactis compared to glucose- or lactose-grown cells.
• Arginine addition upregulated these enzymes, while carbamate kinase activity remained unaffected by growth medium composition.
• Arginine metabolism in S. lactis was sequential with glucose but concurrent with galactose, with efficient energy coupling to growth.
• Glucose limitation induced arginine deiminase in continuous cultures.
• None of the S. cremoris strains exhibited arginine deiminase activity, explaining their inability to metabolize arginine.

Conclusions:

• Growth substrate significantly impacts arginine deiminase pathway enzyme activity in S. lactis.
• The absence of arginine deiminase in S. cremoris explains its metabolic limitations regarding arginine.
• Nutrient availability, particularly glucose limitation, plays a crucial role in regulating arginine metabolism in S. lactis.