MEDIA FOR CULTURING FUNGI
Media
Whatever a particular mould needs, it must always be
supplied with some form of organic carbon for energy, a source of nitrogen for
protein and vitamin synthesis, and several minerals. The substance on which a mould
is grown in the laboratory is called a medium and the mould growing on
it, a culture. Culture media can be solid or liquid, depending on the
sort of information one wishes to obtain. For the purposes of identification,
solid culture media are usually more useful, as they allow the mould to
sporulate more easily.
Solid media
Preparation of solid media involves dissolving a solidifying
agent in the solution that will harden to a gel upon cooling. Agar has the
property of dissolving at a fairly high temperature (nearly that of boiling
water) but solidifying at about 45° C. Thus, it can be poured over living fungi
without killing them, yet can be used for organisms that grow at high
temperature. Agar is relatively stable and cannot be consumed by most organisms.
Liquid media
Liquid media are employed in laboratory work when the entire
colony must be recovered for weighting or chemical extraction. They are also
useful when the culture medium itself is to be analysed for chemical changes.
Type of media:
Most culture media fit into one of three categories: (1)
synthetic, (2) semi-synthetic, and (3) natural.
Synthetic media are composed of ingredients of known
chemical composition and concentration. These media are useful in physiological
or descriptive studies when it is necessary to duplicate exactly a previous
batch of medium or to record the effects of the deletion or addition of a
particular substance.
Semi-synthetic media resemble synthetic media in containing
a known set of ingredients, but differ in that at least some of the ingredients
are of unknown or variable composition. A synthetic medium, in which all
ingredients are chemically defined, can be made semi-synthetic by adding a
substance such as yeast extract.
Natural media are so
called because they are partly or completely composed of natural materials,
such as ground-up (or whole) plants or animals. Some natural media may consist
of a synthetic medium augmented by tomato juice, carrot strips, or plant stems.
Natural media are often very good and allow sporulation in fungi that may
otherwise remain sterile.
[ Most fungi grow
well on media that are high in carbohydrate with pH between 5 and 6 (Bacteria
prefer more protein and pH near 7)].