Getting and storing microbial cultures
The parent strains of all microorganisms were found in nature. Strains used in industry may be far
removed their parents because of modifications through selection, mutation, or recombinant DNA
technology (genetic engineering). Successful companies do not sell their best production strains;
bankrupt companies or those giving up on an unprofitable process may offer their strains for sale.
If these were the best strains in the world for a particular process, the company would probably have
beaten their competitors in the market place.
Reasonably good strains are found in culture collections. By U.S. patent law, a working strain that
will behave as described in the patent must be deposited with a national laboratory. A wise company
would not submit their very best culture. To obtain a strain with which to start a commercial process, a
good strain would have to be the starting point for developing an outstanding strain. A new process
could be started with a strain from nature. There should be a parallel effort to make this strain better.
Selecting strains from nature is greatly facilitated by using culture media that favor microorganisms
with certain characteristics. Enrichment culture is a several step process with a selective medium
that increases the proportions of desired organisms with each step.
Preservation
Some strains of microorganisms will live for quite a while if simply refrigerated. Others can be frozen.
One method for preservation is transfer to fresh solid medium such as nutrient medium to which the
gelling agent agar has been added. Before the cells grow old and die, some are transferred to fresh
medium. This is called serial transfer and could go on forever. Many microorganisms that form
spores (hardy seed-like structure) are allowed to sporulate and then freeze dried (lyophilized). Kept well
below freezing temperature, many types of dried spores will survive for decades or longer.
Next topic on list : microbiology
May 1996