Regulation and function of ammonia-assimilating enzymes in Streptococcus mutans

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Streptococcus mutans is a key pathogen in dental caries.
• Understanding its metabolic capabilities, including amino acid biosynthesis, is crucial for developing targeted interventions.

Purpose of the Study:

• To investigate the capacity of Streptococcus mutans to synthesize amino acids from ammonia.
• To identify the specific enzymatic pathways involved in ammonia assimilation for amino acid biosynthesis in S. mutans.

Main Methods:

• Culturing of Streptococcus mutans strains on defined media lacking amino acids.
• Enzyme assays to detect key enzymes in ammonia assimilation pathways.
• Growth experiments with varying nitrogen sources and isolation of enzyme-deficient mutants.

Main Results:

• Eight of twelve laboratory strains of S. mutans demonstrated anaerobic growth on amino acid-free defined media, indicating ammonia assimilation.
• Strain DR0001 utilized two distinct pathways for ammonia assimilation: a reduced nicotinamide adenine dinucleotide phosphate-coupled glutamate dehydrogenase and a glutamine synthetase/glutamate synthase system.
• Enzyme levels varied with nitrogen source, and glutamate dehydrogenase-negative mutants confirmed pathway functionality.

Conclusions:

• Streptococcus mutans possesses the metabolic flexibility to synthesize essential amino acids via ammonia assimilation.
• The identified pathways, glutamate dehydrogenase and glutamine synthetase/glutamate synthase, are functional in S. mutans and contribute to its nutritional versatility.