Final answer:
Bacteria need specific environmental conditions to grow, including adequate water activity (aw), which is the ratio of the vapor pressure of the medium to that of pure water. Bacteria generally require an aw between 0.97 and 0.99, though some can survive under more extreme conditions.
Step-by-step explanation:
Water Activity and Bacterial Growth
For bacteria to grow, they require specific environmental conditions including the availability of water. The term water activity (aw) is crucial for understanding how bacteria thrive, as it represents the measure of available moisture in a given medium. Water activity is the ratio of the vapor pressure of the medium to the vapor pressure of pure distilled water. Pure water has an aw of 1.0, and bacteria generally require a high aw, typically between 0.97 and 0.99, to sustain growth.
Fungi, on the other hand, can tolerate lower aw levels, which is why drying techniques such as making je_rky, freeze-drying, or adding substances like salt and sugar (to increase osmotic pressure) are effective at preventing microbial spoilage in foods. Specialized bacteria, such as those from the Aquificae class, can even withstand extreme environmental conditions such as high temperatures. Overall, bacteria are incredibly adaptable and have developed various strategies to survive moderate to extreme environments.