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Step 8Maintenance of Stock and Starter Cultures
Stock cultures, otherwise known as master cultures, of the preferred species are the basic foundation of culture. They are normally supplied as monospecific (uni-algal) cultures from reputable culture collections maintained by national institutions or research laboratories. Since they are valuable, they are normally kept in specialized maintenance media, on nutrient enriched agar plates or slopes, under closely controlled conditions of temperature and illumination. A special area or room off the algal culture room is usually allocated to this purpose.
Stock cultures are used only to provide lines of starter cultures (also known as inocula) when required. Every effort should be made to minimize the risk of contaminating the stock and starter cultures with competing microorganisms. The sterile procedures described below should be followed to ensure that contamination does not occur.
Stock cultures are normally kept in small, transparent, sterilizable containers. For example, 500 ml glass, flat-bottomed boiling or conical flasks fitted with a cotton wool plug at the neck, suitable for containing 250 ml of sterile medium, are ideal. Stock cultures are also often maintained in agar medium with suitable nutrients in Petri dishes or on slopes in test tubes.
Stock cultures are best kept in a cooled incubator at 4 to 12ýC (50F) (according to preference), illuminated by low wattage (8W) fluorescent lamps or LED bulbs that provide at least 450 lux.
Alternatively they can be kept in cool conditions close to a north-facing window (out of direct sunlight), or in a cool room illuminated by fluorescent lamps. The objective is not to allow rapid growth, but to maintain the cultures in good condition. The cultures are not aerated, nor is carbon dioxide introduced.
It is necessary to sub-culture stock cultures at monthly intervals to maintain them in a vigorous and healthy state. Simply put 1-1.5 oz stock culture into another reactor containing nutrient medium.
The original stock culture can be kept for a few weeks in the event that the new stock culture fails to grow. The stock culture transfer procedure is best performed in a cabinet that has been sterilized by ultra-violet light to further reduce the risk of contamination.
Stock cultures are used only to provide lines of starter cultures (also known as inocula) when required. Every effort should be made to minimize the risk of contaminating the stock and starter cultures with competing microorganisms. The sterile procedures described below should be followed to ensure that contamination does not occur.
Stock cultures are normally kept in small, transparent, sterilizable containers. For example, 500 ml glass, flat-bottomed boiling or conical flasks fitted with a cotton wool plug at the neck, suitable for containing 250 ml of sterile medium, are ideal. Stock cultures are also often maintained in agar medium with suitable nutrients in Petri dishes or on slopes in test tubes.
Stock cultures are best kept in a cooled incubator at 4 to 12ýC (50F) (according to preference), illuminated by low wattage (8W) fluorescent lamps or LED bulbs that provide at least 450 lux.
Alternatively they can be kept in cool conditions close to a north-facing window (out of direct sunlight), or in a cool room illuminated by fluorescent lamps. The objective is not to allow rapid growth, but to maintain the cultures in good condition. The cultures are not aerated, nor is carbon dioxide introduced.
It is necessary to sub-culture stock cultures at monthly intervals to maintain them in a vigorous and healthy state. Simply put 1-1.5 oz stock culture into another reactor containing nutrient medium.
The original stock culture can be kept for a few weeks in the event that the new stock culture fails to grow. The stock culture transfer procedure is best performed in a cabinet that has been sterilized by ultra-violet light to further reduce the risk of contamination.
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