Which of the following is TRUE of quorum sensing?

Question

BlackTom AI · Accepted Answer

Quorum sensing is a bacterial communication system in which cells secrete, detect, and respond to small signaling molecules called autoinducers; when the extracellular concentration of these molecules reaches a threshold that reflects a high population density, coordinated changes in gene expression occur (e.g., biofilm formation, virulence factor production, bioluminescence).

1. Relevant knowledge points and concepts
- Autoinducers: small diffusible molecules produced and released by bacteria (AHLs in Gram-negatives, oligopeptides in Gram-positives, AI-2 for interspecies signaling).
- Threshold-dependent regulation: accumulation of autoinducer scales with cell density; once concentration exceeds a threshold, receptor-mediated regulation activates target genes.
- Positive feedback: many quorum sensing systems increase autoinducer synthase expression after detection, amplifying the signal and synchronizing the population.

2. Step-by-step reasoning
- Determine the core feature of quorum sensing: sensing population density via extracellular signals (autoinducers) that modify gene expression collectively.
- Compare each option to that core feature to evaluate truthfulness.

3. Calculations/intermediate steps
- No numerical calculations are required. Conceptual “threshold” logic: low cell density → low autoinducer concentration → no response; high cell density → high autoinducer concentration → response.

4. Why the correct answer is correct
- "Quorum sensing is used by bacteria to sense a high population of other cells" directly states the central mechanism: bacteria infer population density from accumulated autoinducer levels and coordinate group behavior. This succinctly captures the essential definition and function of quorum sensing.

5. Why the other options are incorrect
- "Sensing an autoinducer shuts down synthesis of that autoinducer": generally false; many systems use positive feedback to upregulate synthase after sensing, not shut it down (though regulatory complexity exists, the statement as absolute is incorrect).
- "Quorum sensing is useful for a single cell": incorrect because the system’s benefit arises from coordinated group behaviors; a lone cell cannot reach autoinducer thresholds to trigger population-level responses.
- "Two component systems are always using quorum sensing": incorrect; two-component systems are a broad class of bacterial signal transduction mechanisms and are not synonymous with quorum sensing, although some QS systems may use two-component-like regulators.

6. Conclusion
The correct answer is: quorum sensing is used by bacteria to sense a high population of other cells — this matches the provided answer.

Which of the following is TRUE of quorum sensing?单项选择题

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