Forms of cultures

For our purposes, it is useful to distinguish between the following forms of cultures:

• A culture should be referred to as a pure culture if it contains only one species of diatoms.
• An axenic culture, on the other hand, is present when there are no other organisms besides the desired ones. In particular, it must be free from bacteria. This is only possible in a professionally equipped laboratory and has never been our personal goal.
• Clonal is a culture when it has emerged from a single cell, so that in the case of exclusively asexual reproduction all the diatoms are genetically identical.
• In a batch culture the nutrient medium is added once. The growth of culture comes to a standstill if one of its components has a limiting effect.
• Often one understands by a permanent culture a culture with a continuous supply of nutrient medium. A permanent culture is in this context to be understood as a culture which exists over an extended period of time, this means, over many generations. A series of batch cultures (repeated culturing of new cultures from parent cultures) can make this possible.

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