The ComEA/ComEC Operon is Critical for Nitrosative Stress Tolerance by an Oral Commensal

Area of Science:

• Microbiology
• Oral Biology
• Molecular Biology

Background:

• Oral commensal streptococci, like Streptococcus parasanguinis, are crucial for maintaining oral microbial homeostasis.
• Hydrogen peroxide (H2O2) produced by S. parasanguinis reacts with salivary nitrite (NO2) to form antimicrobial peroxynitrite (ONOO-).
• S. parasanguinis exhibits remarkable resistance to NO2 and ONOO-, but the underlying mechanisms are unknown.

Purpose of the Study:

• To identify the mechanisms by which S. parasanguinis tolerates NO2-mediated nitrosative stress.
• To investigate the role of the ComEA/ComEC DNA uptake operon in S. parasanguinis's resistance and physiology.

Main Methods:

• Transcriptomics analysis to identify upregulated genes under NaNO2 exposure.
• Genetic manipulation to create a comEA/comEC deletion mutant.
• Phenotypic assays to assess sensitivity to peroxynitrite, biofilm development, intracellular nitrite transport, and H2O2 production.
• In vivo colonization studies using a Drosophila melanogaster model.

Main Results:

• Transcriptomics revealed upregulation of the DNA uptake gene comEA during growth with NaNO2.
• Deletion of the ComEA/ComEC locus led to increased sensitivity to peroxynitrite.
• Loss of ComEA/ComEC resulted in reduced biofilm formation, impaired intracellular nitrite transport, and decreased H2O2 production.
• The comEA/comEC mutant was defective in colonization in the Drosophila melanogaster model.

Conclusions:

• The ComEA/ComEC DNA uptake operon is essential for S. parasanguinis's resistance to nitrosative stress.
• This operon plays a critical role in S. parasanguinis physiology, including biofilm development and H2O2 production.
• The ComEA/EC DNA uptake system is potentially vital for S. parasanguinis colonization and its role in modulating oral cavity homeostasis.