Subculture and Preservation Methods
Some microorganisms are sensitive to environmental stress, such as freezing or drying, which can lead to rapid death. In such cases, the subculture preservation method is often the most effective approach. Subculture involves the regular transfer of microbial strains from one culture medium to another, allowing them to be maintained over time. This is one of the most commonly used techniques for preserving microbial cultures, especially for everyday strains like those used in yogurt production.
When performing subculturing, it's important to maintain a balanced medium. The concentration should not be too high, and the nutrient content should be moderate, particularly reducing the carbohydrate levels. The incubation temperature is usually set slightly below the optimal growth temperature to slow down metabolic activity. For acid-producing strains, adding a small amount of calcium carbonate to the medium can help neutralize the acidic environment.
Most microbial strains are best preserved at around 5°C. However, certain organisms, such as anaerobic bacteria, *Vibrio cholerae*, and some pathogenic fungi, may require higher temperatures, typically around 37°C. Large edible fungi, like mushrooms, can often be stored at room temperature without issues.
While subculture is a simple and cost-effective method, it does have several drawbacks. First, the cotton plugs used in culture tubes are prone to mold contamination. Second, the genetic stability of the strain may decrease over time, leading to mutations. Third, repeated subculturing can reduce the pathogenicity, physiological activity, and spore-forming ability of the microorganism. Additionally, this method requires frequent transfers, increasing the workload. Lastly, there is a higher risk of contamination during each step of the process.
There are many other preservation methods available, such as cryopreservation, lyophilization, and storage in glycerol. Due to space limitations, we’ve only covered the basics here. If you're interested in learning more about microbial preservation techniques, feel free to download our full guide. Click the download button to get the file for free. Don’t forget to unzip it after downloading!
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