Page 228 - Algae Anatomy, Biochemistry, and Biotechnology

Algal Culturing 211

TABLE 6.1
Shape Codes and Corresponding Dimensions Required for Calculating Biovolumes of
Various Phytoplankton Species
Dimensions Required
Shape Code Length Width Depth Diameter
Cone CON L W
Cylinder CYL L W DP D
Dumbell box DBB L W DP
Dumbell DBL L W DP
Diamond box DMB L W DP
Fusiform FUS L W
Ovoid box OVB L W DP
Ovoid OVO L W
Rectangular box RTB L W DP
Sphere SPH D
Teardrop TRP L W

CULTURE TYPES
A culture can be defined as an artificial environment in which the algae grow. In theory, culture
conditions should resemble the alga’s natural environment as far as possible; in reality many sig-
nificant differences exist, most of which are deliberately imposed. In fact, following isolation from
the natural environment, algal strains are maintained under largely artificial conditions of media
composition, light, and temperature. The imposition of an artificial environment on a cell popu-
lation previously surviving under complex, fluctuating conditions and following a seasonal life
cycle inevitably causes a period of physiological adaptation or selection, during which population
growth will not occur or is very slow.
While contaminated algal cultures have previously been satisfactory for certain application and
experiments, modern experimental methods and application demand that contaminants are not gen-
erally present, and that the taxonomy and growth characteristics of strains are defined. Hence, for
most purposes, algal cultures are maintained as unialgal, contaminant-free or axenic stocks. “Uni-
algal” cultures contain only one kind of alga, usually a clonal population (but which may contain
bacteria, fungi, or protozoa), whereas “axenic” cultures should contain only one alga and no bac-
teria, fungi, or protozoa.
To obtain a unialgal culture one species must be isolated from all the rest; three major tech-
niques borrowed from microbiology are available for obtaining unialgal isolates: streaking and suc-
cessive plating on agar media, serial dilution, and single-cell isolations using capillary pipettes.
Streaking is useful for single-celled, colonial, or filamentous algae that will grow on an agar
surface. Filaments can be grabbed with a slightly curved pipette tip and dragged through soft
agar (less than 1%) to remove contaminants. It is best to begin with young branches or filament
tips that have not yet been extensively epiphytized.
Many flagellates, however, as well as other types of algae must be isolated by single-organism
isolations or serial-dilution techniques. A particularly effective means of obtaining unialgal cultures
is isolation of zoospores immediately after they have been released from parental cell walls, but
before they stop swimming and attached to a surface. Recently released zoospores are devoid of