Which signaling system in Streptococcus mutans triggers genetic competence for DNA uptake?

• A. AI-2 system.
• B. CSP triggers genetic competence for DNA uptake via the ComDE system.
• C. Quorum sensing does not influence competence.
• D. LuxS produces CSP.

Answer: (B)

Genetic competence in Streptococcus mutans is controlled by a peptide-based quorum-sensing system—the competence-stimulating peptide that signals through the ComDE two-component system. The CSP is produced and secreted; as the bacterial population grows, CSP accumulates and binds the sensor kinase ComD. This triggers autophosphorylation of ComD and transfer of the phosphate to the response regulator ComE. Phosphorylated ComE activates transcription of early competence genes and promotes the expression of comX, encoding an alternative sigma factor that drives the late competence genes needed for DNA uptake machinery. The result is a competent state that allows uptake of external DNA. The AI-2 system involving LuxS is a separate quorum-sensing pathway and does not trigger this CSP-ComDE competence cascade, so CSP—not LuxS-derived AI-2—is the key signal for triggering genetic competence in this organism.