Our main article "In-vitro aquarium plants" already describes the many unique characteristics associated with aquarium plants cultivated using the in-vitro method. In this article, we will explain the conditions under which in vitro plants are cultivated, and how to deal with any possible infestation by mould or bacteria.

In-vitro plants are normally supplied in sterile cups, which means that the plants are free from foreign organisms such as algae or bacteria. However, by working under non-sterile conditions e.g. while planting in the laboratory or during shipping, various microorganisms may enter the cups. The most common causes of contamination in in-vitro plants are moulds, bacteria and yeasts. Since the culture medium also provides ideal conditions for many of these microorganisms, showing exponential growth rates under good conditions, contamination can in some cases easily overgrow the entire culture overnight.
Due to their rapid growth, the microorganisms consume nutrients in the medium and damage the plant by excreting toxins and waste products from its metabolism. Especially at higher temperatures it can happen that a pot is completely inconspicuous before shipping, but arrives at the customer in a very bad condition.

Fungi

Fungi usually enter the culture as spores and are the most common cause of contamination in in-vitro pots outside the laboratory. There they germinate and after a short time form a dense mycelium, which becomes visible as wadden- to fur-like vegetation. Depending on the type of fungus, the plant itself, the medium or both serve as the food basis. Irrespective of the type of infestation, fungi usually overgrow the entire cup within a very short time. For the plant, this usually means death, as the fungus either poisons it with its excreta, removes the nutrients contained in the medium or actively attacks it.
If the plants still look vital despite a fungal infestation, they can be used in the aquarium without hesitation after thorough cleaning and removal of the culture medium. Any fungal threads remaining on the plant will find very unfavourable living conditions under water and will quickly be displaced by the beneficial microorganisms of the predominant biofilm.

Mould inside the in-vitro cup

Yeasts

Yeasts are unicellular fungi and are a rarer source of contamination of in-vitro plants. They are usually introduced into the cultures by unmindful laboratory staff during propagation. Due to their short generation time, contamination with yeasts becomes visible within a few days as turbidity in the liquid medium or as slimy growth on the surface of the solid medium. As a rule, the adult plants in the sales pot are not damaged by such yeast contamination and can be used without hesitation in the aquarium after thorough cleaning. Due to metabolic fermentation processes of the yeasts, however, an unpleasant odour, such as that known from fermented or spoiled foods, can sometimes occur when the pots affected are opened.

Yeast in liquid medium

Bacteria

Bacteria primarily pose a problem during the establishment of fresh in-vitro cultures from non-sterile raw materials. Both in the pots and in the sterile culture of whole plants, nutrients crucial for the growth of bacteria, such as increased sugar concentrations, are often missing in the medium. They are therefore among the rarer contaminations and are only mentioned here for sake of completeness.

Similar to contamination with fungi, bacteria can also lead to the spoilage of an in-vitro pot within a very short time. Due to their short generation time, they usually completely overgrow the cultures within two to three days and cause severe damage to the plant through their excreta.

Bacteria

Endophytes

Endophytes are microorganisms such as fungi or bacteria that live in the cells or intracellular spaces of a plant. While some representatives of this group of living organisms are pathogens that actively damage the plant, other species may even have a symbiotic relationship to their host. Under normal conditions, these microorganisms always remain inside the plant as they find their optimal habitat here. In in-vitro culture, however, endophytes may also spread into the medium, which also provides them with an abundant food source. As a rule, however, such growth is concentrated in the area of the plant that is in direct contact with the medium. Complete overgrowth of the culture or damage to the plants by endophytes is extremely rare. After opening the pots, these microorganisms can be washed off together with the medium and the plant can be placed in the aquarium as normal.

Endophytes