Challenges

All in all, it does not require much effort or special knowledge to cultivate some species and keep them alive for a period of months. Cultivation of various species of the genera Navicula, Nitzschia, Pinnularia, Cymatopleura, Cymbella or Rhopalodia proved to be quite unproblematic. The nutrient solution was never adapted specifically for one species. Only in light intensity did we occasionally consider an individual requirement.

At this point, however, it should not be concealed that one can run into difficulties with the cultivation of diatoms. From our experience these are above all:

1. Some species are difficult to cultivate. It often requires some trials until the cultivation succeeds (see example). For others, it seems hardly possible by simple means. If you do not want to cultivate a particular genus or species, you can see that relaxed.
   
   
2. In the case of asexual reproduction, the average length of the diatoms is reduced in each generation (Pfitzer and MacDonald). This phenomenon has already been pointed out in the introduction. If a sequence of batch cultures is generated by regularly creating new cultures, one always transfers a sample of diatoms of different lengths. The subsequent culture can produce no larger diatoms than its largest diatom without the sexual reproduction. The dying of the largest diatoms also leads to the fact that the lengths of the diatoms in culture are becoming smaller and smaller.
   
   Sexual reproduction (or vegetative cell enlargement) is now required but is difficult to achieve in vitro. We could not recognize sexual reproduction in our cultures with only a few exceptions. (We would be very grateful for hints on how to create suitable conditions for sexual reproduction.)
   
   The gradual reduction in the length of the diatoms thus led to a limited durability of the sequence of cultures. Whereas species of Navicula have been preserved for only a few months, it has been possible to cultivate lines of Pinnularia or Rhopalodia for years.
   
   In addition, malformations of the frustules frequently occurred in long-term cultivation. This can be caused in particular by decreasing valves or by symptoms of deficiency (examples: Surirella and Nitzschia, Cymatopleura solea).
   
   
3. At the beginning of a series of batch cultures, contamination with other diatoms, green algae, flagellates, or bacteria may occur. If the cultures are handled without care, this can happen even later. Here a very clean process helps in the cultivation. The sterilization of pipettes, the choice of a favorable diameter of the pipettes and the washing of diatoms in intermediate baths were addressed. Furthermore, one should avoid leaving petri dishes open for a longer period of time.

The difficulties mentioned should not discourage you, because a good looking culture compensates for some trouble.

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