Definition for Subculture
From Biology Forums Dictionary
In Biology, a subculture is a new cell or microbiological culture made by transferring some or all cells from a previous culture to fresh growth medium. This action is called subculturing or passaging the cells. Subculture is used to prolong the life and/or expand the number of cells or microorganisms in the culture.
Role
Cell lines and microorganisms cannot be held in culture indefinitely due to the gradual rise in toxic metabolites, use of nutrients and increase in cell number due to growth. Subculture is therefore used to produce a new culture with a lower density of cells than the originating culture, fresh nutrients and no toxic metabolites allowing continued growth of the cells without risk of cell death. Subculture is important for both proliferating (e.g. a microorganism like E. coli) and non-proliferating (e.g. terminally differentiated white blood cells) cells.
Typically subculture is from a culture of a certain volume into fresh growth medium of equal volume, this allows long-term maintenance of the cell line. Subculture into a larger volume of growth medium is used when wanting to increase the number of cells for, for example, use in an industrial process or scientific experiment.
Passage number
It is often important to record the approximate number of divisions cells have had in culture by recording the number of passages or subcultures. In the case of plant tissue cells somaclonal variation may arise over long periods in culture. Similarly in mammalian cell lines chromosomal aberrations have a tendency to increase over time. For microorganisms there is a tendency to adapt to culture conditions, which is rarely precisely like the microorganisms natural environment, which can alter their biology.