Microplastic Biofilms in Pond Water

ISEF Category: Microbiology

Subcategory: Environmental Microbiology  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

A tiny plastic bead can become a floating apartment building for microbes. That biofilm changes how the particle moves, sinks, and interacts with the ecosystem. Your local pond can turn into a natural test site for asking which materials attract the most life. This project connects microbiology, ecology, and environmental pollution in one experiment.

What Is It?

Microplastics are small plastic pieces, often from broken-down larger plastics. Once they sit in water, they do not stay bare for long. Bacteria and other microbes stick to the surface and form a biofilm, a slimy layer of cells plus their own secreted glue. Think of it like a crowded neighborhood that builds itself on each bead.

Different materials may host different biofilms. A polyethylene bead, a PET bead, a PLA bead, and a glass bead do not present the same surface chemistry. Surface chemistry means the material’s outer properties, like charge, roughness, and how water interacts with it. Those differences can affect how many microbes attach, how thick the biofilm gets, and which taxa show up in sequencing data.

Why This Is a Good Topic

This is a strong science fair topic because you can test a real environmental question with clear measurements. You can compare biofilm mass, then pair that with community data from 16S amplicon sequencing to see whether material type changes both quantity and composition. The project connects plastic pollution, freshwater ecology, and microbial growth, which gives you a real-world story. You can also build useful research skills, like experimental design, sample labeling, controls, and data analysis.

Research Questions

• How does bead material affect biofilm density after pond incubation? ?
• What is the effect of bead material on bacterial community composition compared with matched pond water? ?
• Does PLA support a different biofilm density than PE, PET, and glass beads? ?
• To what extent do biofilm alpha diversity measures differ across bead types? ?
• Which taxa become enriched on plastic beads relative to water samples? ?
• How does bead surface roughness relate to crystal violet signal? ?

Basic Materials

• PE beads or pellets with known size and source.
• PET beads or pellets with known size and source.
• PLA beads or pellets with known size and source.
• Glass beads matched by size to the plastic beads.
• Fine mesh sample bags or inert mesh holders.
• Waterproof labels and a permanent marker.
• Gloves and safety glasses.
• Digital balance with 0.001 g accuracy.
• Crystal violet stain.
• Distilled water.
• Micropipettes and sterile tips.
• Clear tubes or 96-well plates for staining reads.
• Smartphone or plate reader for color measurement.
• Cooler with ice packs for sample transport.
• Sample collection tubes for sequencing aliquots.
• Field notebook or digital lab notebook.

Advanced Materials

• Autoclave or sterile filtration setup for media and buffer prep.
• Laminar flow hood for clean sample handling.
• Spectrophotometer or microplate reader for crystal violet quantification.
• DNA extraction kit validated for biofilm samples.
• PCR setup with 16S primers.
• Agarose gel electrophoresis equipment.
• Access to amplicon sequencing through a mentor or core facility.
• Sterile forceps and scissors.
• Vortex mixer and bead-beating tubes.
• Centrifuge with tube adapters for small volumes.
• Refrigerated storage for extracted DNA.
• Negative control materials for extraction and PCR.
• Positive control DNA or mock community, if available.

Software & Tools

• QIIME 2: Processes 16S sequencing reads and helps compare community composition across sample types.
• R: Runs statistics and makes graphs for biofilm density and diversity measures.
• ImageJ: Measures stained area or intensity from photos when a plate reader is not available.
• Excel: Organizes sample metadata, staining values, and field notes.
• Google Sheets: Lets you track sample IDs and share data with a mentor.

Experiment Steps

1. Define the comparison you want to make, such as plastic type versus glass control, and write one primary outcome for biofilm mass and one for microbial community shift.
2. Plan your sampling design so each material gets matched replicates from the same pond, same location, and same exposure window.
3. Choose a measurement plan for biofilm density, then decide how you will turn stain intensity into a consistent number.
4. Set up sequencing controls, including matched water samples, blank extraction controls, and any negative PCR controls your mentor recommends.
5. Build a metadata table before fieldwork so every bead set has a unique ID, location, date, and handling history.
6. Pre-plan the statistical tests you will use for density differences and community comparisons, so you do not decide the analysis after seeing the results.

Common Pitfalls

• Using beads that differ in size or color, which confounds material effects with surface area and optics.
• Missing true field replicates, which makes one pond spot look like a material effect.
• Letting samples dry unevenly before crystal violet staining, which changes stain retention between tubes.
• Comparing sequencing reads without matched water controls, which makes it hard to tell attachment from the background pond community.
• Mixing up sample IDs during field recovery or DNA extraction, which breaks the link between density data and 16S results.

What Makes This Competitive

A class-level version of this project stops at a few stain measurements. A stronger version asks sharper questions about surface chemistry, controls, and community structure. You can raise the level by matching bead size, adding rigorous field replicates, and separating attachment effects from background pond microbes. Strong analysis, such as beta diversity testing and enrichment comparisons, can turn simple observation into real ecological insight.

Project Variations

• Compare biofilm growth on microplastics from different brands or polymer sources to see whether manufacturing differences matter.
• Add a sunlight or shaded-site comparison to test whether environmental exposure changes both biofilm mass and community shifts.
• Replace crystal violet with microscopic image analysis to compare surface coverage, thickness, and patchiness on each bead type.

Learn More

• NCBI PubMed: Search review articles on microplastic biofilms, freshwater microbiomes, and 16S amplicon analysis.
• NOAA Marine Debris Program: Read background on plastic pollution, biofouling, and environmental transport of debris.
• USGS Water Science School: Find plain-language materials on freshwater sampling, watersheds, and water-quality context.
• NIH 16S rRNA Sequencing resources: Look for tutorials and background on amplicon sequencing and microbial community analysis.
• QIIME 2 documentation: Learn the standard workflow for processing 16S sequencing data and comparing communities.