[Campbell Biology P.446] The flashlight fish hosts Vibrio bacteria that emit light through t... | Practice Question

The flashlight fish hosts Vibrio bacteria that emit light through the activity of lux genes. This light emission only occurs when the bacteria reach a certain density quorum . Based on this information and general principles of gene regulation, which of the following hypotheses best explains how lux gene expression is regulated in response to bacterial density?

  • A: High bacterial density leads to increased degradation of *lux* gene mRNA.
  • B: Bacteria at high density secrete an autoinducer molecule that activates *lux* gene transcription.
  • C: Low bacterial density triggers a repressor protein to bind to the *lux* operon, preventing light production.
  • D: The fish's immune system activates *lux* gene expression when bacterial numbers are sufficient.

Explanation

This scenario perfectly describes quorum sensing, a mechanism where bacteria communicate using secreted signaling molecules autoinducers . When bacterial density is low, the autoinducer concentration is low, and lux genes are not expressed. As density increases, the autoinducer accumulates. Once it reaches a threshold concentration, it binds to a receptor, typically an activator protein, which then promotes the transcription of lux genes, leading to a synchronized light emission.