Inspired by Louis Pasteur's swan-neck flask experiment, a microbiology student was interested in repeating this experiment using hay (dried grass) infusion instead of nutrient broth. He placed a few strands of dried grass into a sugar solution in an open neck flask, drew the neck of the flask into a swan-neck shape using a flame and then boiled the contents of the flask for 30 minutes. After 3 days of incubation at room temperature he was surprised to see bacterial growth in the flask.Does this experiment support spontaneous generation? If not, how would you explain the growth bacteria in the flask?

Bacterial endospores. Some bacteria, specially from the phylum Firmicutes, produce endospores. An endospore is a resistance form of the bacteria, which is not reproductive. This form of the bacteria is resistant to heat, UV radiation, drought, cold, and might remain dormant for long periods. The formation of the endospores is triggered by starvation. In the experiment mentioned, instead of nutrient broth, which production is controled, a hay infusion is used. Since this is a material picked up from the soil, there is a high possibility of the presence of the endospores, could be from Bacillus, since this genera of bacteria is widely present in the soil. Once the endospores are in a suitable envoronment (culture media) they will stop dormancy and became metabolically active. It is mentioned that the culture media was boiled for 30 minutes, and endospores are resistant at 100 °C for several hours.

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