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LIST OF CULTURE MEDIA
Details of some of the more useful maintenance media,
referred to by number in the list of strains, are given
below. Special media and methods for algae are
given by Venkataraman (1969) and Stein (1973);
for parasitic protozoa by Taylor and Baker (1978);
for free living protozoa by Page (1981), and for
various microorganisms in a CRC Handbook by
Rechcigl (1978). The water used should always be
distilled or deionised (unless the contrary is
stated). Sterilization is by autoclaving at 15 lb/in2
(ca 1 bar or 101 kPa) for 15 min unless stated other—
wise.
Mention of a particular supplier does not imply that
other products are necessarily less satisfactory.
Medium M1
This medium is satisfactory for many algae; it quickly
reveals the presence of most contaminants. For agar
cultures with bacteria, a less rich medium is necessary
such as soil extract agar (e + s).
Medium M2 (e + s)
KNO3
K2HPO4
MgSO4.7H20
Agar
Soil extract stock solution
g per 100 ml water
0.02
0.002
0.002
1.0
10% by volume
The soil extract stock solution is made by heating in
a steamer a calcareous garden loam with twice its
volume of supernatant water for 2 hours, or by
autoclaving for 15 min. It is convenient to make up
and sterilize a number of small containers of stock
solution each of a size appropriate to making a batch
of media, as repeated autoclaving is deleterious.
5.1
SOIL AND WATER MEDIA
These simple media have great advantages for many
purposes, so long as axenic culture is not required,
and may produce excellent growth of almost any
organism apart from the more exacting planktonic
and parasitic forms.
Medium M3 Basic biphasic medium
Put a layer about 1 cm deep of good calcareous
garden loam into a test tube or jar. (The use of
mud from rivers or ponds is seldom satisfactory.)
Carefully add water to a depth of 7 to 10 cm, plug
or cover, and steam for one hour (longer for larger
vessels) on each of 2 consecutive days; further
sterilization is not needed. Allow to stand for a
further day before inoculating, when the pH should
be between 7 and 8.
Many variations of this basic medium are possible.
The garden soil can be replaced by calcareous clay
(Medium M3i). The addition of a little (about 3% of
the volume of the soil) calcium carbonate or
ammonium magnesium phosphate beneath the soil is
recommended, the former (Medium M3ii) for many
eutrophic Chlorophyceae, the latter (Medium M3iii) for
many green euglenids. Sphagnum peat may be added
or may replace the soil when growing forms from
acid habitats (Medium M3iv). The addition of a little
starch below the soil stimulates growth of many
saprophytes like Polytoma and Astasia (Medium M3v).
A grain of pearl barley, rice or wheat produces a
bacterial flora forming suitable food for many
ciliates (Medium M3vi).
When selecting soils, it is advisable to take a fair—sized
sample, about one cubic foot or 30 litres, pass this
through a sieve of about 1 cm mesh and then make
up media and test them with appropriate organisms.
If the sample is satisfactory, sufficient stock is then
available for many batches of medium.