Stock Preservation or Culture
Preservation
The culture used to initiate a fermentation process must be viable and free from
contamination, so it has to be preserved to eliminate contamination, genetic
changes and to retain viability. The organism is kept viable by repeated subculture
in fresh media. But each time a cell divide during sub culturing there is a chance for
mutation. Repeated sub culturing involves many divisions resulting in variation and
contamination and microorganisms that carry out new fermentations or which
provide higher yield are of economic value and they have to be preserved.
Maintenance of stock culture plays an important role in industrial fermentation
researches and production. The organism can be preserved for short term or long
term depending on the purpose. Accordingly there are two types of preservation;
Short term and Long term.
1. Short term preservation
Short term preservation involves maintenance of cultures for up to one year. Most
fungal cultures can be maintained for that period by serial transfer. The method is
simple, inexpensive and widely used. Although time consuming and labour
intensive, periodic transfer is a good option for small collections with cultures in
constant use for short periods (less than one year).the method also has several
disadvantages however cultures must be checked frequently for contamination by
mites or other microorganisms and for drying. In addition the morphology and
physiology of a cultured fungus may change over time.in particular the ability to
sporulate or to infect host may be lost after repeated transfers because of those
disadvantages the technique is generally in appropriate for long term (more than 1
year) preservation of cultures.
Periodic transfer to fresh media
Strains can be maintained by periodically preparing a fresh culture from the previous
stock culture. The culture medium, the storage temperature and the time interval at
, which the transfers are made vary with the species and must be asserted
beforehand. The temperature and type of medium chosen should support a slow
rather than a rapid rate of growth so that the time interval between transfers can be
as long as possible.
They are of two types:
Working stock and Primary stock
I. Working stock - These are used frequently and should be maintained as an
agar slant, agar stab, spore preparations or broth cultures and they are held
under refrigeration. The cultures are checked constantly for detecting the
changes in growth characteristics, mutation, productive capacity and
contamination.
II. Primary stocks - These are cultures held in reserve for new fermentation, for
comparative purposes, biological assays, for screening programs. Transfer
from primary stock is done when it is sub cultured to avoid the death of the
cells. Primary stock cultures are stored at room temperature in sterile soil,
agar or broth which is provided with an overlay of sterile mineral oil. Agar and
broth cultures without mineral oil can be refrigerated.
2. Long term Preservation
Storage by refrigeration: Culture media medium can be successful is stored in
refrigerators or cold rooms when the temperature is maintained at 40 C. At this
temperature range the metabolic activities of microbes slowdown greatly and
only small quantity of nutrients will be utilized. This method cannot be used for
a very long time because toxic product to get accumulated which can kill the
bacteria.
Storage at low temperature: Cultures grown on agar slants are stored in
O
freezers at -20 C and sub cultured at approximately 6 months of interval.
The time duration can be extended if the slant is over layered with mineral oil.
Preservation
The culture used to initiate a fermentation process must be viable and free from
contamination, so it has to be preserved to eliminate contamination, genetic
changes and to retain viability. The organism is kept viable by repeated subculture
in fresh media. But each time a cell divide during sub culturing there is a chance for
mutation. Repeated sub culturing involves many divisions resulting in variation and
contamination and microorganisms that carry out new fermentations or which
provide higher yield are of economic value and they have to be preserved.
Maintenance of stock culture plays an important role in industrial fermentation
researches and production. The organism can be preserved for short term or long
term depending on the purpose. Accordingly there are two types of preservation;
Short term and Long term.
1. Short term preservation
Short term preservation involves maintenance of cultures for up to one year. Most
fungal cultures can be maintained for that period by serial transfer. The method is
simple, inexpensive and widely used. Although time consuming and labour
intensive, periodic transfer is a good option for small collections with cultures in
constant use for short periods (less than one year).the method also has several
disadvantages however cultures must be checked frequently for contamination by
mites or other microorganisms and for drying. In addition the morphology and
physiology of a cultured fungus may change over time.in particular the ability to
sporulate or to infect host may be lost after repeated transfers because of those
disadvantages the technique is generally in appropriate for long term (more than 1
year) preservation of cultures.
Periodic transfer to fresh media
Strains can be maintained by periodically preparing a fresh culture from the previous
stock culture. The culture medium, the storage temperature and the time interval at
, which the transfers are made vary with the species and must be asserted
beforehand. The temperature and type of medium chosen should support a slow
rather than a rapid rate of growth so that the time interval between transfers can be
as long as possible.
They are of two types:
Working stock and Primary stock
I. Working stock - These are used frequently and should be maintained as an
agar slant, agar stab, spore preparations or broth cultures and they are held
under refrigeration. The cultures are checked constantly for detecting the
changes in growth characteristics, mutation, productive capacity and
contamination.
II. Primary stocks - These are cultures held in reserve for new fermentation, for
comparative purposes, biological assays, for screening programs. Transfer
from primary stock is done when it is sub cultured to avoid the death of the
cells. Primary stock cultures are stored at room temperature in sterile soil,
agar or broth which is provided with an overlay of sterile mineral oil. Agar and
broth cultures without mineral oil can be refrigerated.
2. Long term Preservation
Storage by refrigeration: Culture media medium can be successful is stored in
refrigerators or cold rooms when the temperature is maintained at 40 C. At this
temperature range the metabolic activities of microbes slowdown greatly and
only small quantity of nutrients will be utilized. This method cannot be used for
a very long time because toxic product to get accumulated which can kill the
bacteria.
Storage at low temperature: Cultures grown on agar slants are stored in
O
freezers at -20 C and sub cultured at approximately 6 months of interval.
The time duration can be extended if the slant is over layered with mineral oil.
