# DBT JRF 2022 — Question 59

Exam: DBT JRF 2022 · Section: B · Topic: Microbiology › Quorum Sensing · Difficulty: Medium

## Question

A bacterial signaling system that regulates population density-dependent gene expression using secreted chemical signals is known as:

## Options

- **A.** G protein-coupled receptor signalling
- **B.** Quorum sensing
- **C.** Receptor-mediated signalling
- **D.** Two component system

## Answer

Option B

## Explanation

Quorum sensing in bacteria: Quorum sensing (QS) is a cell density-dependent gene regulation mechanism: 1. Bacteria continuously secrete small diffusible signalling molecules called autoinducers (AIs): • Gram-negative: N-acyl homoserine lactones (AHLs) — e.g., LasI/LasR in Pseudomonas aeruginosa • Gram-positive: short oligopeptides (AIPs) • Universal: AI-2 (furanosyl borate diester) 2. As population density increases, autoinducer concentration accumulates. 3. When [autoinducer] exceeds a threshold, it binds its receptor → transcription factor activated → gene expression changes. Genes regulated by QS include: biofilm formation, virulence factors, bioluminescence (Vibrio fischeri), antibiotic synthesis. Key concept: QS allows bacteria to 'sense' population density and coordinate collective behaviour (act as a multicellular community). Answer: Quorum sensing uses secreted autoinducers that accumulate with population density to regulate gene expression at a threshold.

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