Uptake of carbon and phosphorous from an agar medium

The uptake of these two nutrients can easily be visualized by a simple technique (Fig 13). Fungi are grown on top of a cellophane membrane on a defined agar medium containing glucose and minerals (including phosphorous). The fungus cannot penetrate the membrane but can take up small molecular compounds through the membrane. When the fungal colony has grown out the outline of the colony can be marked on the bottom of the Petri dish and the colony can be removed by lifting off the membrane. The presence of glucose or phosphorus can the be detected in the agar medium by placing a filter paper with a reagent that reacts to produce a coloured product were a glucose or phosphorus is present. Glucose can for example be detected by its ability to reduce copper (Fig 14) and phophorus by its reaction to molybdate ions (Fig 15).

Fig 13. Technique for visualizing the uptake of a nutrient from an agar medium.

Fig 13. Technique for visualizing the uptake of a nutrient from an agar medium.

Fig 14. Uptake of glucose. Presence of glucose is detected by a precipitation of 'brown Cu2O when glucose reduce Cu2+(EDTA). The outer red line shows the outline of the fungal colony. Note that the fungus takes up basically all glucose under the colony.

Fig 14. Uptake of phosphorus. Presence of glucose is detected by a the reaction with molybdate creating a blue colour. The dashed line shows the outline of the fungal colony. Note that the fungus takes up basically all phosphorus under the colony.

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