Penicillium is a widespread genus of fungi, commonly recognized as blue or green molds. This group is historically significant as the source of the antibiotic penicillin and for its role in producing certain cheeses. This guide outlines the necessary steps to safely grow Penicillium for educational observation, emphasizing these cultures are not for medicinal use or consumption.
Understanding Penicillium and Safety Precautions
Penicillium is a genus within the kingdom Fungi, encompassing over 300 species known for their brush-like spore-bearing structures. These fungi are saprophytic, obtaining nutrients from dead organic materials and playing a role in natural decomposition. Penicillium species are found globally in soil, air, and indoors where moisture is present. They are notable for producing penicillin, a revolutionary antibiotic, and contributing to the distinct flavors of blue cheeses.
Handling mold cultures requires careful attention to safety. Molds produce spores, which, when inhaled, may trigger allergic reactions like respiratory issues or skin irritation in sensitive individuals. Some Penicillium species also produce mycotoxins, toxic compounds that can pose health risks if ingested or inhaled. Home cultivation also carries the risk of contamination from other, potentially more harmful molds or bacteria. Therefore, homemade cultures are not suitable for consumption or medical application.
Protecting yourself during cultivation is important. Wear personal protective equipment (PPE) like gloves, eye protection, and an N95 respirator mask to prevent direct contact and spore inhalation. Establish a dedicated workspace in a well-ventilated area, separate from food preparation zones or high-traffic areas, to minimize contamination and accidental exposure.
Preparing for Cultivation
Successful Penicillium cultivation requires preparing the growing environment and materials. Essential items include sterile Petri dishes, a growth medium like agar, and transfer tools. Potato Dextrose Agar (PDA) is a common choice for molds, available pre-made or prepared from scratch. If preparing agar at home, use a pressure cooker for sterilization to eliminate microbial life.
After sterilizing, pour the agar into sterile Petri dishes in a clean, still-air environment to prevent airborne contaminants. Allow the agar to cool and solidify, forming a nutrient-rich surface. Create a sterile workspace by wiping surfaces with 70% isopropyl alcohol and minimizing air currents by closing windows and turning off fans.
Spores can be sourced from common items, such as mold on a decaying orange or lemon, or from blue cheese, which contains Penicillium roqueforti or Penicillium camemberti. While natural sources are convenient, they increase the likelihood of co-culturing other microorganisms. For more controlled results, specific Penicillium cultures can be obtained from biological supply companies.
The Cultivation Process
To inoculate, gently touch a sterile cotton swab to mold on a natural source, then lightly streak it across the agar surface in the Petri dish. For blue cheese, transfer a tiny scraping with a sterile tool. Open and close the Petri dish lid quickly during transfer to minimize exposure to airborne contaminants.
After inoculation, seal the Petri dish to protect the culture and prevent the agar from drying. Parafilm or tape can be used around the edge, ensuring some gas exchange. Label the dish with the date and source for tracking.
Place inoculated dishes in an incubation area. Penicillium species thrive at room temperature, typically 20-25°C (68-77°F). Keep cultures in a dark or dimly lit, stable, undisturbed spot away from direct sunlight, drafts, or significant temperature fluctuations. Within a few days, small white spots should become visible on the agar surface.
Maintaining and Observing Growth
As the Penicillium culture develops, its appearance changes. Initially, colonies may appear as small white, fuzzy patches. Visible growth typically begins within 2 to 5 days, maturing over 7 to 14 days. Mature mold develops the characteristic blue-green or greenish-gray coloration from colored spores. Growth often exhibits a radial pattern, expanding outwards.
Distinguish desired Penicillium growth from potential contaminants like brightly colored molds, black molds, or slimy bacterial colonies. If a culture shows contamination, safely dispose of it to prevent the spread of unwanted microorganisms. For prolonged observation, cultures can be stored in a refrigerator, which slows growth.
Safe Handling and Disposal
Maintain safety protocols when handling cultures. Wear gloves, eye protection, and a mask, especially once sporulation is evident, to prevent spore release and inhalation. Keep dishes sealed to contain the mold.
When the experiment is complete, sterilize the entire sealed Petri dish before discarding. Place the sealed dish in a plastic bag and then into a pressure cooker for 20 to 30 minutes, or submerge it in a 10% bleach solution for several hours or overnight. After sterilization, dispose of the double-bagged dish with regular household waste. Thoroughly clean and disinfect the work area and reusable tools with 70% isopropyl alcohol or a bleach solution.