Growing mold in a petri dish can be a fascinating way to observe fungi up close, offering insights into their growth patterns and life cycles. This simple experiment is an accessible project for learning about microbiology. By setting up a controlled environment, you can safely explore the world of these ubiquitous organisms from the comfort of your home. It provides a hands-on opportunity to understand how environmental factors influence fungal development.
Essential Supplies
To cultivate mold, gather the right materials. Sterile petri dishes provide a clean, contained space for mold growth, and a growth medium, such as agar, supplies nutrients for the fungi. While specialized agar can be purchased, common household items like plain gelatin mixed with sugar and beef bouillon, or even a slice of bread, can serve as alternative growth media. Cotton swabs transfer mold spores, and distilled or sterile water prepares the medium and moistens the environment. A source of mold spores (from fruit, soil, or airborne particles) is necessary to initiate growth.
Cultivating Your Mold Culture
Cultivating mold begins with preparing the growth medium. For agar or gelatin, dissolve the powder in water (often with gentle heating), then pour the warm liquid into sterile petri dishes, filling them one-third to one-half full. Allow the medium to cool and solidify into a jelly-like consistency.
For a simpler approach, place a moistened slice of bread directly into a petri dish. Once the medium is prepared, introduce mold spores using a cotton swab. Gently rub the swab over a mold-suspected surface (e.g., old fruit, dusty area, houseplant soil), then transfer the spores onto the medium. Alternatively, leave the petri dish open for 15-30 minutes to collect airborne spores, then close the lid.
After inoculation, seal the petri dish with tape to prevent contamination and spore escape. Place the sealed dish in a warm, dark, undisturbed location (ideally 75-80°F / 24-27°C) for optimal fungal growth. Mold typically shows visible growth within 3 to 7 days, with some varieties appearing in 48 hours. Maintaining a consistent temperature and avoiding direct sunlight helps ensure the mold develops properly.
Safety Guidelines
Careful attention to safety is required when working with mold cultures. Once mold growth is visible, avoid opening the petri dish to prevent spore release. Inhaling mold spores can cause allergic reactions, respiratory problems, or sensitivities, especially for those with compromised immune systems or pre-existing lung conditions. Some molds produce mycotoxins, toxic compounds whose presence cannot be determined visually; caution is always advisable.
Always wear gloves (e.g., household rubber gloves) when handling petri dishes, especially during setup and disposal, to avoid direct skin contact with mold or medium. Wear eye protection (e.g., goggles) to prevent spores from entering the eyes. After contact with the petri dish or materials, thoroughly wash hands with soap and water. Never consume anything that contacted the mold culture or growth medium, and conduct the experiment away from food preparation surfaces.
Observing Your Mold Growth
Observe your mold culture through the sealed petri dish, without opening it, to prevent spore release. Mold growth typically becomes visible within days, starting as small, fuzzy spots that gradually expand. You will likely observe various colors (green, black, white, yellow, orange) as different mold species develop. Mold color is influenced by species, nutrient source, age, and environmental conditions, but color alone does not indicate toxicity. For instance, many molds can appear green, including common genera like Aspergillus, Penicillium, and Cladosporium.
As the mold colony matures, you might notice texture changes, from powdery to slimy or furry. Document observations by logging date, size, color, and texture, or by taking daily photographs for a time-lapse record. Concentric rings or distinct growth patterns, characteristic of certain fungal colonies, may also be observed. The growth rate can vary, with some molds expanding rapidly while others grow more slowly.
Proper Disposal
Proper disposal of the mold culture is important for safety once observations are complete. Securely seal the petri dish, reinforcing it with additional tape to ensure no spores escape. Do not open the petri dish or wash its contents, as this could release harmful spores. Instead, place the sealed petri dish into a durable plastic bag (e.g., resealable freezer bag) and seal it.
For added safety, deactivate the mold before disposal. Deactivation can be achieved by adding bleach solution to the sealed dish (if possible without opening) or by placing the sealed bag with the dish into another bag containing a bleach-soaked paper towel for 24 hours in a well-ventilated area. Dispose of the double-bagged, deactivated mold culture in household trash. Avoid pouring mold-contaminated liquids down the drain, as this introduces spores into plumbing.