Final answer:
The two common methods of preserving microbial cultures for long periods are lyophilization(freeze-drying) and refrigeration, with lyophilization being particularly effective for long-term storage. Filtration is a method that physically removes microbes without killing them or inhibiting their growth.
Step-by-step explanation:
The two common methods of preserving microbial cultures for long periods are lyophilization and refrigeration. Lyophilization, or freeze-drying, is a method where an item is rapidly frozen and then put under a vacuum.
This process allows water to be lost by sublimation, which preserves the item's original qualities and allows for long-term storage of microbial cultures, even at room temperature if packaged properly. Refrigeration slows microbial growth, and certain types of laboratory cultures can be preserved by refrigeration for later use.
The physical method of microbial control that removes microbes physically from samples but doesn't kill them or inhibit their growth is filtration. Other methods such as heating and desiccation (drying) can kill or control microbial growth by disrupting membranes and denaturing proteins.