Subculture (biology)

In biology, a subculture refers to a new cell or microbial culture made by transferring a portion of an existing (parent) culture to a fresh growth medium. This process is also known as "passaging" or "splitting" a culture. Subculturing is performed to propagate cells or microorganisms, maintain viable cultures, and study their properties under controlled conditions.

The primary reasons for subculturing include:

• Preventing nutrient depletion: As cells or microorganisms grow, they consume nutrients in the medium. Subculturing to fresh medium replenishes these nutrients.
• Removing toxic byproducts: Metabolic byproducts accumulate over time and can inhibit growth or even be toxic. Transferring to fresh medium dilutes these byproducts.
• Maintaining cell viability: Overcrowding and the accumulation of waste products can lead to cell death. Subculturing ensures a healthy and actively growing population.
• Obtaining sufficient biomass: Subculturing allows for the expansion of the culture to obtain a sufficient quantity of cells or microorganisms for experimental use or other applications.
• Maintaining genetic stability (for cell lines): Regular subculturing can help maintain the desired characteristics of a cell line, although this can also contribute to genetic drift over many passages.
• Long-term storage (cryopreservation): Before cells or microorganisms can be cryopreserved (frozen for long-term storage), they are often subcultured to ensure a healthy and robust population.

The subculturing process typically involves:

1. Aseptic technique: All steps are performed under sterile conditions to prevent contamination.
2. Harvesting cells: Cells or microorganisms are collected from the parent culture (e.g., by scraping, centrifugation, or enzymatic digestion).
3. Dilution: The harvested cells or microorganisms are diluted in a suitable medium.
4. Inoculation: A small aliquot of the diluted suspension is transferred to a new culture vessel containing fresh growth medium.
5. Incubation: The new subculture is incubated under appropriate conditions (temperature, humidity, atmosphere) to allow for growth.

The frequency of subculturing depends on the growth rate of the cells or microorganisms, the type of medium, and the experimental goals. It's critical to document the passage number (the number of times a culture has been subcultured) to track potential changes in cell characteristics and ensure reproducibility of experiments.