Rooftop Dust Microbes and UV Tolerance

ISEF Category: Microbiology

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

The Hook

Some microbes can survive sunlight better than you would expect, even on dusty rooftops. That matters because UV resistance can shape which microbes spread through air and survive on buildings. You can turn that idea into a real project by asking which rooftop colonies survive UV-C and why. The answer may connect color, survival, and genes that protect cells from light damage.

What Is It?

This project asks a simple question with a tricky twist, which microbes on rooftop dust can survive strong UV light? Rooftop dust acts like a tiny landing pad for bacteria and fungi carried by wind, skin, soil, and pollen. After UV exposure, some colonies die fast, while others keep growing. That difference can point to protective traits such as pigments.

Pigments are colored molecules that can act like tiny sunscreen. Carotenoids, for example, often make colonies yellow, orange, or red, and they can help cells handle light stress. If you compare pigment strength with UV survival, you may see whether color predicts tolerance. You can also compare close relatives in genome databases to see whether likely carotenoid genes match the survival pattern you observed.

Why This Is a Good Topic

This is a strong science fair topic because you can measure a clear outcome, survival after UV exposure, and change one variable at a time. The project connects to air quality, building surfaces, microbial ecology, and how life copes with radiation stress. You can learn plate-based microbiology, basic dose-response analysis, and how to connect lab results with genome database searches.

Research Questions

• How does UV-C dose affect the survival rate of rooftop dust isolates?
• What is the effect of colony pigmentation intensity on UV-C survival?
• Does the source surface on the rooftop change the mix of UV-tolerant colonies?
• To what extent do pigmented isolates survive better than nonpigmented isolates after UV-C exposure?
• Which closest-relative genomes contain carotenoid biosynthesis genes that match the phenotype of the isolated colonies?
• How does repeated UV-C exposure change survival across successive subcultures?

Basic Materials

• Sterile settle plates or agar plates suitable for environmental isolation.
• Sterile swabs or inoculation loops.
• Disposable gloves and lab coat.
• UV-C sterilization lamp with known output rating.
• UV-blocking face shield or goggles rated for UV-C work.
• Parafilm or plate sealing film.
• Permanent marker for labeling plates.
• Digital camera or smartphone for colony photos.
• Ruler or calipers for colony size reference.
• Computer with spreadsheet software for data entry.

Advanced Materials

• Access to a microbiology incubator.
• Class II biosafety cabinet or equivalent clean workspace.
• Spectrophotometer or plate reader for pigment or turbidity measurements.
• Fluorometer for DNA quantification.
• PCR setup with thermal cycler.
• Agarose gel electrophoresis equipment.
• DNA extraction kit.
• Access to 16S rRNA gene sequencing or whole-genome sequencing service.
• Bioinformatics workstation with internet access.
• UV-C radiometer for dose verification.

Software & Tools

• ImageJ: Measures colony color intensity, area, and growth changes from photos.
• Google Sheets: Organizes survival data and calculates basic statistics.
• R: Fits survival curves and tests whether pigmentation predicts UV tolerance.
• NCBI BLAST: Finds closest relatives for your isolates and suggests candidate pigment genes.
• PubMed: Helps you find review articles and methods papers on UV tolerance and carotenoid biosynthesis.

Experiment Steps

1. Define the rooftop sampling plan and decide which dust sources, colony types, and UV exposure levels you will compare.
2. Set up a way to score pigmentation and growth so you can turn visual differences into numbers.
3. Plan a dose-response design that gives you a survival curve instead of a single before-and-after result.
4. Choose controls that separate UV effects from drying, handling, and plate-to-plate variation.
5. Map out how you will identify the closest relatives of each isolate and connect genome hits to pigment pathways.
6. Decide in advance which statistics will test whether color predicts survival better than chance.

Common Pitfalls

• Using different lighting when photographing colonies, which makes pigment scores impossible to compare.
• Choosing only the darkest colonies, which biases the sample before you test survival.
• Skipping UV dose verification, which leaves you unsure whether each plate got the same exposure.
• Mixing up desiccation effects with UV effects, which can make dead cells look like UV-sensitive cells.
• Trying to compare too many isolate types at once, which turns the project into a messy screen instead of a clear study.

What Makes This Competitive

A stronger version of this project goes beyond a simple survival test. You would quantify pigmentation, verify UV dose carefully, and use a real dose-response curve instead of one exposure level. You could also compare rooftop sites, isolate types, or predicted pigment genes across close relatives. That kind of design gives you clearer biology and a better story about how environmental microbes survive light stress.

Project Variations

• Compare rooftop dust isolates from shaded and sun-exposed buildings to see whether exposure history changes UV tolerance.
• Use visible-light stress instead of UV-C to test whether pigment still predicts survival under a different kind of light damage.
• Focus on one microbial group, such as pigmented bacteria or yeast-like fungi, and compare pigment score with genome-based pathway predictions.

Learn More

• NCBI: Search genome records and gene annotations for carotenoid biosynthesis pathways.
• PubMed: Search for review articles on UV resistance, microbial pigments, and carotenoids.
• NIH NCBI Bookshelf: Read free microbiology and molecular biology chapters for background on DNA damage and repair.
• ASM Journals: Search for peer-reviewed studies on environmental microbiology and pigment-mediated stress tolerance.
• MIT OpenCourseWare: Look for free microbiology or genomics course materials that explain experimental design and sequence analysis.
• NOAA: Explore air and atmospheric science resources that help connect rooftop dust to environmental transport.