Soil Streptomyces Antibiotic Screening Project Ideas

ISEF Category: Microbiology

Subcategory: Antimicrobials and Antibiotics  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

Most of the antibiotics we use started with a dirt sample. That makes your local soil a tiny drug discovery lab. You can hunt for Streptomyces, the bacteria that make many natural antibiotics, and rank the strongest isolates by how well they stop a test microbe. Then you can connect those results to DNA clues about what kinds of compounds they may make.

What Is It?

This project asks you to prospect for Streptomyces in soil. Prospecting means searching for likely producers of useful compounds. Streptomyces are a group of filamentous bacteria that live in soil and often make molecules that slow or kill other microbes. Think of them like tiny chemical factories that compete with neighbors by releasing antibiotics.

You start by isolating candidates on selective media such as glycerol-arginine agar, which favors the growth of many Streptomyces while suppressing some faster-growing contaminants. Then you test each isolate with an overlay assay against B. subtilis, a safe lab strain often used as a target because it grows well and shows clear inhibition zones. Bigger clear zones suggest stronger antibacterial activity, but the size alone does not tell you the full story.

You can add a genetics layer by sending 16S Sanger amplicons for sequencing. The 16S rRNA gene acts like a bacterial ID barcode. After you BLAST the sequence, you compare the closest genome relatives and inspect antiSMASH predictions for biosynthetic gene clusters. Those clusters are the DNA instructions for making secondary metabolites, including many antibiotic-like compounds.

Why This Is a Good Topic

This is a strong science fair topic because you can measure several things at once, colony traits, inhibition strength, and sequence-based identity. The project connects directly to antibiotic discovery, which matters because bacteria keep evolving resistance. You also get room to ask a real research question, not just collect pretty plates. A student can learn isolation, screening, basic bioinformatics, and data ranking without needing a full research lab career first.

Research Questions

• How does the soil source, such as garden, park, compost, or roadside soil, affect the number of Streptomyces isolates you recover?
• What is the effect of selective glycerol-arginine agar versus a less selective general medium on Streptomyces isolation success?
• Does colony morphology score, such as powdery texture, aerial growth, or pigment production, predict inhibition zone size against B. subtilis?
• To what extent does sample depth in the same soil site change the chance of finding antibacterial Streptomyces?
• Which environmental feature, such as pH, moisture, or vegetation cover, best predicts the strongest antibacterial isolates?
• How does the closest BLAST match of the 16S sequence relate to antiSMASH biosynthetic gene cluster classes in the nearest genome relative?

Basic Materials

• Soil samples from several local sites, collected in sterile containers.
• Selective glycerol-arginine agar plates or prepared medium.
• Sterile inoculating loops and sterile swabs.
• Incubator set to an appropriate microbial growth temperature.
• Petri dishes for isolation and overlay assays.
• Safe B. subtilis test strain from a school or university lab.
• Permanent marker for plate labeling.
• Digital camera or phone camera with fixed mounting.
• Ruler or calipers for measuring inhibition zones.
• Disposable gloves, lab coat, and eye protection.
• Biohazard waste container and disinfectant approved by the lab.
• Notebook or spreadsheet for isolate tracking.

Advanced Materials

• Access to a biosafety-approved microbiology workspace.
• Autoclave or validated sterilization access.
• Micropipettes and sterile filtered tips.
• Agarose gel electrophoresis setup for checking PCR products.
• PCR thermocycler for 16S amplification.
• DNA extraction kit or approved colony prep method.
• Sanger sequencing service for 16S amplicons.
• Computer with internet access for BLAST and genome database searches.
• Genome browser or antiSMASH access for biosynthetic gene cluster comparison.
• Reference strains or positive controls for inhibition assays.
• Image analysis setup for standardized plate photography.
• Sterile saline or buffer for isolate handling.
• Cryostorage supplies for archiving promising isolates.

Software & Tools

• NCBI BLAST: Compares your 16S sequence to known bacteria and helps you find the closest matches.
• antiSMASH: Predicts biosynthetic gene clusters in related genomes so you can infer what kinds of compounds an isolate may make.
• ImageJ: Measures inhibition zone diameter from plate photos and helps you keep scoring consistent.
• Google Sheets: Organizes isolate data, sample metadata, and summary statistics in one place.
• R: Runs simple statistics and plots that compare sites, isolates, and inhibition strength.

Experiment Steps

1. Define your sampling plan and decide which soil features you will compare first.
2. Choose one isolation medium and one screening target so your first pass stays focused.
3. Set up a ranking system for colony appearance, growth quality, and inhibition zone size.
4. Plan how you will confirm identity with 16S sequencing and BLAST comparison.
5. Select a small subset of promising isolates for deeper genome-relative analysis with antiSMASH.
6. Build a data table that links soil metadata, isolate traits, and bioactivity results.

Common Pitfalls

• Picking random colonies without recording the exact soil source, which makes your best isolate impossible to trace back to an environmental pattern.
• Using plates that are too crowded, which causes overlapping colonies and ruins your ability to rank isolates fairly.
• Scoring inhibition zones from photos taken under different lighting, which changes apparent zone size from plate to plate.
• Treating a big inhibition zone as proof of a new antibiotic, which ignores whether the effect came from growth rate, diffusion, or competition.
• Comparing 16S names without checking genome relatives, which can make your antiSMASH predictions too vague to say much about the chemistry.

What Makes This Competitive

A competitive version of this project does more than find a few inhibitory colonies. You would build a clean sampling design, compare sites with clear environmental variables, and use standardized image analysis for every plate. You would also connect phenotype to genotype by pairing 16S identity with genome-relative biosynthetic predictions instead of stopping at colony morphology. Strong statistics, good controls, and a clear claim about which soils or isolate traits predict antibacterial activity would make the project much stronger.

Project Variations

• Compare Streptomyces from urban, suburban, and natural soils to see which habitat yields the strongest antibacterials.
• Swap B. subtilis for a different safe indicator strain approved by your lab to test whether activity looks broad or narrow.
• Focus on one environmental gradient, such as pH or moisture, and ask whether it predicts both isolate abundance and inhibition strength.

Learn More

• USDA NRCS Soil Survey Manual: Use this to understand soil properties and find background on sampling environments, available through USDA and university libraries.
• NCBI BLAST help pages: Learn how to compare your 16S sequence to reference bacteria, found through the NCBI website.
• NIH NCBI Bookshelf: Search for free microbiology and molecular biology chapters that explain bacterial identification and gene clusters.
• antiSMASH publication and documentation: Read the software paper and docs to understand biosynthetic gene cluster prediction, available through the antiSMASH site and journal search.
• ASM Microbiology Education resources: Find free teaching materials on microbial isolation, antibiotic discovery, and safe lab practice on the American Society for Microbiology site.