MICROBIAL CULTURE PRESERVATION/GENERAL MICROBIOLOGY AND MICROBIAL DIVERSITY

1. Periodic Transfer (Subculturing) The simplest and oldest method, involving the routine transfer of microbes to fresh media. How it works: Microbes are inoculated onto an agar slant or broth, allowed to grow, and then stored in a refrigerator (typically at 4°C). Duration: Few weeks to a few months, depending on the organism. Drawbacks: High risk of contamination, human error, and genetic mutations over time due to repeated cell division. 2. Storage Under Mineral Oil (Overlay Method) A modification of subculturing that extends the life of the slant. How it works: A sterile layer of liquid paraffin or mineral oil is poured over a fresh agar slant culture. Mechanism: The oil prevents dehydration of the medium and limits oxygen availability, drastically slowing down metabolic activity. Duration: 1 to 2 years. Long-Term Preservation (Gold Standards) 3. Cryopreservation (Deep Freezing) Preservation at ultra-low temperatures where metabolic activity stops entirely. How it works: Cultures are frozen at temperatures ranging from -70°C to -196°C (using liquid nitrogen). The Role of Cryoprotectants: Direct freezing creates ice crystals that can shred cell membranes. To prevent this, protective chemicals like glycerol (usually 15-20%) or dimethyl sulfoxide (DMSO) are added to act as an "antifreeze." #study #college #biology #microbiology #students