Moulds such as Penicillium grow as long, branching threads called hyphae, which form a tangled network called a mycelium. Their cells are not separate, so they cannot be counted with a haemocytometer or by dilution plating. Instead, growth is measured as an increase in area or mass.Area of a colony
A fungal colony on an agar plate spreads outwards as a roughly circular patch. Measure its diameter with a ruler across the base of the plate. Colonies are rarely perfect circles, so measure two diameters at right angles and take the mean. Then calculate the area:area = πr2 Worked example: the two diameters are 22 mm and 26 mm. The mean diameter is 24 mm, so r = 12 mm.area = 3.14 × 122 = 452 mm2 Repeating this each day shows how fast the colony grows.Mass
A fungus grown in liquid broth can be separated from the broth by filtering. Wet mass is unreliable, because the amount of water held by the mycelium varies. It is better to find the dry mass: the fungus is dried in a warm oven and weighed repeatedly until the mass stops changing (constant mass), showing all the water has gone.Dry mass is the most accurate measure of the biomass, but it kills the fungus, so a separate culture is needed for each time point. Area measurement does not harm the fungus but only shows growth across the surface, not how thick the mycelium is.
A fungal colony on an agar plate spreads outwards as a roughly circular patch. Measure its diameter with a ruler across the base of the plate. Colonies are rarely perfect circles, so measure two diameters at right angles and take the mean. Then calculate the area:
A fungus grown in liquid broth can be separated from the broth by filtering. Wet mass is unreliable, because the amount of water held by the mycelium varies. It is better to find the dry mass: the fungus is dried in a warm oven and weighed repeatedly until the mass stops changing (constant mass), showing all the water has gone.Dry mass is the most accurate measure of the biomass, but it kills the fungus, so a separate culture is needed for each time point. Area measurement does not harm the fungus but only shows growth across the surface, not how thick the mycelium is.