Quorum Sensing With CV026 Biosensor

ISEF Category: Microbiology

Subcategory: Bacteriology  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Bacteria do not just grow, they vote. Many species release small signal molecules and change behavior when enough neighbors join in. You can spy on that chemical conversation with a color-changing biosensor. That gives you a real shot at original research with a clear measurement.

What Is It?

Quorum sensing is how bacteria sense crowd size. They release small molecules called autoinducers, including AHLs, short for acyl-homoserine lactones. When the signal builds up, cells switch genes on or off together. That can control pigment, virulence, biofilm formation, and other group behaviors.

Chromobacterium violaceum CV026 is a biosensor strain that helps you detect AHL activity. When it senses the right signal, it makes violacein, a purple pigment. Think of it like a light-up lock. If an extract contains an AHL-like agonist, the color turns on. If it blocks the signal, the color drops. You can compare extracts from plants and spices, then use smartphone colorimetry to turn that purple shift into numbers.

Docking adds a second layer. Docking is a computer method that estimates how a molecule might fit into a protein pocket, in this case CviR, the quorum-sensing receptor. Your wet-lab data tells you what happens. Your docking results help explain why. That mix of biology and computation makes the project much stronger.

Why This Is a Good Topic

This is a strong science fair topic because you can test real biological signaling with a visible readout. You are not just guessing from a plant name or spice label. You can compare many natural extracts, measure dose response, and connect the result to a molecular mechanism. That gives you a clear research question, real data, and room for deeper analysis.

Research Questions

• How does extract source affect violacein production in CV026?
• What is the effect of extract concentration on CV026 violacein intensity?
• Does a plant extract act as an AHL agonist or an AHL antagonist in the CV026 assay?
• To what extent do spice extracts differ in their EC50 values for CV026 activation?
• Which solvent extraction method produces the strongest quorum-sensing effect in a given plant sample?
• How does predicted CviR binding strength compare with measured color response across extracts?
• What is the effect of combining two extracts on CV026 violacein intensity?

Basic Materials

• BSL-1 approved Chromobacterium violaceum CV026 culture from an educational supplier or supervised lab source.
• Standard sterile agar plates and broth approved by your lab.
• A known AHL positive control, such as a supplier-approved synthetic standard.
• A known negative control solvent.
• Plant leaves, seeds, herbs, or spice samples.
• Small glass vials or sterile microcentrifuge tubes.
• Disposable pipette tips and micropipettes.
• Digital kitchen scale or analytical balance.
• Smartphone with a camera.
• White background or light box for consistent photos.
• Free color analysis app or ImageJ on a computer.
• Gloves, lab coat, and eye protection.
• Biohazard waste containers and disinfectant approved by your lab.

Advanced Materials

• Purified AHL standards for calibration and dose-response curves.
• Multiple solvent systems for extract fractionation.
• Spectrophotometer or microplate reader for pigment validation.
• 96-well plates and sterile plate seals.
• Centrifuge for clearing extract particles before testing.
• HPLC or LC-MS access for chemical profiling.
• Molecular docking software and a workstation.
• Protein structure file for CviR from a public database.
• Open-source chemistry software for ligand preparation.
• Reference quorum-sensing inhibitors for comparison.
• Statistical software for regression and model fitting.

Software & Tools

• ImageJ: Measures violet pigment intensity from standardized smartphone images.
• Python: Fits dose-response curves and compares EC50 values across extracts.
• AutoDock Vina: Predicts how candidate molecules may bind to CviR.
• PubChem: Helps you find structures and basic properties of plant and spice compounds.
• R: Runs statistics, plots, and model checks for your bioassay data.

Experiment Steps

1. Define whether you are screening for quorum-sensing activation, inhibition, or both.
2. Choose a small, chemically diverse set of plants or spices so your comparisons mean something.
3. Plan extraction and cleanup methods that keep pigment and debris from distorting the biosensor readout.
4. Build a calibration strategy with positive and negative controls so you can convert color into response values.
5. Set up a dose-response design that lets you estimate EC50 or inhibition strength from the biosensor data.
6. Match the wet-lab results with docking predictions and decide how you will test whether the two agree.

Common Pitfalls

• Using extracts that are so dark or cloudy that the purple signal gets hidden in the background color.
• Forgetting to include solvent-only controls, which makes it impossible to tell signal from extraction residue.
• Comparing photos taken under different lighting, which breaks smartphone color measurements.
• Treating every purple change as activation, even when an extract may block growth or interfere with pigment chemistry.
• Docking random plant compounds without preparing the CviR structure and ligands in a consistent format.

What Makes This Competitive

A class-level version of this project stops at a few color comparisons. A stronger project uses real controls, repeated dose-response curves, and a clean analysis plan for EC50 or inhibition strength. You can also raise the level by comparing docking scores with measured bioactivity, then checking where they agree and where they fail. That shows you can think like a researcher, not just run an assay.

Project Variations

• Screen herbal teas, not just spices, to compare water-soluble quorum-sensing activity.
• Compare crude extracts with solvent-fractionated extracts to see which chemical class drives the signal.
• Test a known quorum-sensing inhibitor alongside food extracts to benchmark your biosensor response.

Learn More

• PubMed: Search for review articles on quorum sensing, AHLs, and Chromobacterium violaceum CV026 to find background and methods.
• NIH PubMed Central: Read free full-text papers on violacein biosensors and natural quorum-sensing modulators.
• NCBI Bookshelf: Look for microbiology chapters on bacterial communication and gene regulation.
• NOAA/USGS plant and natural products resources: Use public databases to connect sample choice with known chemistry and ecology.
• MIT OpenCourseWare: Search for free biology and biochemistry course notes that explain receptor binding, dose-response, and data analysis.