106. A bacterial signaling system that regulates population density-dependent gene expression
using secreted chemical signals is known as:
A. G protein-coupled receptor signalling
B. Quorum sensing
C. Receptor-mediated signalling
D. Two component system

Detailed Explanation:

Quorum sensing is a unique cell-to-cell communication process used by bacteria to coordinate gene expression according to the density of their population. This system involves the production, release, and detection of signaling molecules called autoinducers.

As the bacterial population grows, the concentration of autoinducers increases. Once a threshold concentration is reached, it triggers a signal transduction cascade that leads to changes in gene expression. This allows bacteria to act collectively—a behavior not seen when they exist individually.

Examples of Processes Regulated by Quorum Sensing:

• Biofilm formation

• Virulence factor production

• Antibiotic production

• Bioluminescence (e.g., Vibrio fischeri)

Why It’s Not the Other Options:

• G protein-coupled receptor signaling is typical in eukaryotes, not bacteria.

• Receptor-mediated signaling is a broader term and not specific to population-dependent gene regulation.

• Two-component systems involve a sensor kinase and a response regulator, often in response to environmental changes, not population density.

Correct Answer:

B. Quorum sensing

Conclusion:

Quorum sensing enables bacteria to behave like a multicellular organism, coordinating group activities through chemical messages. It plays a vital role in microbial ecology, pathogenesis, and biotechnology, making it a key area of research in microbiology and synthetic biology.