|Posted on Thursday, January 02, 2003 - 01:56 pm:||
Question: What are common contaminants of the mushroom culture?
Answer: Most specialty mushrooms are grown on sterilized substrates, and once a contaminant gets a foothold, it flourishes in the absence of competition from other contaminants. In nature, complex interactions among hundreds of other fungi, bacteria, nematodes, etc. maintain an ecological equilibrium. In a sterilized medium, the grower provides ideal conditions for the contaminant to prosper. In sawdust bags, contamination usually involves another fungus living off the waste products or on the remains of the cultivated fungus, or sometimes on the living mycelium or fruiting body of the cultivated fungus. The only competition for these contaminants is the cultivated fungus itself.
Wet Spot; Sour Rot - Bacillus sp.
In grain spawn jars, one commonly encounters Bacillus, which sometimes survives the sterilization process as heat resistant endospores. . A dull gray to mucus-like brownish slime characterized by a strong but foul odor variously described as smelling like rotting apples, dirty socks or burnt bacon. Bacillus makes uncolonized grain appear excessively wet, hence the name "Wet Spot". Pallid to whitish ridges along the margins of individual grain kernels characterize this contaminant. Bacillus primarily reproduces through simple cell division. In times of adverse environmental conditions, especially heat, a single hardened spore forms within each parent cell body - bacterial endospores, which can survive high temperatures for prolonged time.
The most practical method for eliminating bacterial endospores involves soaking the grain at room temperature 12 - 24 hours prior to sterilization. Endospores, if viable, will germinate within that time frame and then be susceptible to standard sterilization procedures. And, new endospores won't form in the moist environment of the resting jar of grain.