E. coli Conjugation Kinetics Study

ISEF Category: Microbiology

Subcategory: Microbial Genetics  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Bacteria can pass DNA like a text message, and some plasmids spread fast enough to reshape entire populations. If you can model that transfer rate, you can ask when the system speeds up, slows down, or shuts itself off. That gives you a real genetics question, not just a growth experiment. You also get a chance to connect math, microbiology, and public health.

What Is It?

Bacterial conjugation is one way bacteria share DNA. In this project, donor E. coli cells carry an F plasmid, a small DNA circle that can move into recipient cells. Think of the plasmid like a shared flash drive. When a donor meets a recipient, the donor can copy and send the plasmid across a contact bridge.

Your job is to measure how fast that transfer happens under different conditions. Two big variables matter here. One is the donor to recipient ratio, which changes how often cells meet. The other is the mating environment, surface versus liquid, which changes how long cells stay in contact. A mass-action model treats transfer like a collision-based process, so you can test whether real data follow the same pattern.

Why This Is a Good Topic

This is a strong science fair topic because you can change clear variables, measure a real biological outcome, and compare your data to a mathematical model. It connects directly to antibiotic resistance, since plasmids often carry resistance genes and spread them through bacterial groups. You can learn experimental design, statistics, and model fitting, which are all useful for higher-level research. The project also leaves room for a real hypothesis, not just a demonstration.

Research Questions

• How does the donor to recipient ratio affect conjugation frequency in E. coli K-12 mating assays?
• What is the effect of surface mating versus liquid mating on plasmid transfer rate?
• Does conjugation follow a mass-action model across different donor to recipient ratios?
• To what extent does the transfer rate change after the first high-transfer phase in a mating assay?
• Which mating condition produces the highest number of transconjugants per donor cell?
• How does contact environment change the time course of plasmid spread in a mixed population?

Basic Materials

• F-plasmid-bearing E. coli K-12 educational strain
• Recipient E. coli K-12 educational strain
• Selective agar plates for donor, recipient, and transconjugant screening
• Sterile Petri dishes
• Micropipettes and sterile tips
• Sterile microcentrifuge tubes
• Inoculating loops or sterile spreaders
• Incubator approved for school or research lab use
• Digital colony counter or manual counting grid
• Laboratory notebook
• PPE, including gloves, lab coat, and eye protection.

Advanced Materials

• Spectrophotometer or plate reader for cell density normalization
• Refrigerated centrifuge for sample handling
• Shaking incubator for controlled liquid matings
• Biofilm-compatible surface materials for contact assays
• Fluorescence or selectable marker system for transconjugant tracking
• PCR setup for confirming plasmid transfer
• Gel electrophoresis equipment
• Colony PCR reagents
• Sterile filtration supplies for liquid mating controls
• Statistical software for kinetic model fitting.

Software & Tools

• R: Fits conjugation models, compares conditions, and runs statistical tests.
• Python: Organizes raw counts, graphs transfer curves, and automates model fitting.
• ImageJ: Helps count colonies or analyze plate images when manual counting gets messy.
• GraphPad Prism: Makes dose-response style plots and compares group means with clear statistics.
• NIH ImageJ macros: Speeds up repeated image analysis for many plates or time points.

Experiment Steps

1. Define the transfer outcome you will measure, such as transconjugant count, transfer frequency, or rate constant.
2. Choose one independent variable to test first, then hold the rest of the mating conditions fixed.
3. Plan your control groups so you can separate true plasmid transfer from contamination or mixed culture growth.
4. Build a counting and normalization strategy before you start, so your data can be compared across plates and trials.
5. Fit your data to a mass-action model and decide which parameter will tell you whether transfer slows after heavy mating.
6. Compare surface and liquid conditions with the same analysis pipeline, then check whether the model still matches both settings.

Common Pitfalls

• Using the wrong selective plates, which makes donor, recipient, and transconjugant colonies hard to tell apart.
• Skipping cell density normalization, which makes one mating setup look faster only because it started with more cells.
• Assuming every colony is a true transconjugant, which inflates transfer rates when spontaneous mutants or cross-feeders appear.
• Letting surface and liquid assays run under slightly different handling conditions, which confounds contact mode with stress from the procedure.
• Fitting a mass-action model to a single time point, which cannot show whether transfer rate changes after an early burst.

What Makes This Competitive

A stronger project would measure transfer over multiple time points, not just before and after. It would also compare the model to real data instead of stopping at a simple bar graph. If you test whether the transfer rate changes after the early high-transfer phase, and back that up with clean controls, your work starts to look like a real research study. Clear statistics and careful strain confirmation matter a lot here.

Project Variations

• Test how conjugation changes when the recipient strain carries a different selectable marker or stress response mutation.
• Compare conjugation on agar, in broth, and on a moist filter surface to see how contact mode changes transfer kinetics.
• Analyze whether plasmid transfer differs when you quantify colonies by manual counting versus image-based counting.

Learn More

• NCBI Bookshelf: Search for free textbook chapters on bacterial conjugation and plasmids.
• PubMed: Search for review articles on conjugation kinetics, F plasmids, and bacterial gene transfer.
• NIH NCBI Gene: Look up E. coli genes and plasmid-related terms to check strain background details.
• ASM journals: Search peer-reviewed microbiology articles on plasmid transfer and conjugation models.
• MIT OpenCourseWare: Find free microbiology and genetics course materials for background on plasmids and bacterial DNA transfer.