Introduction to Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 10

3 μm

1 μm

Figure 1.4 Prokaryote features of
blue-green algae. Top right: Phase-
contrast (light microscope) image of
live filamentous colony of Anabaena ,
showing central patches of pale
chromatin (Ch). Top left: Transmis-
sion electron micrograph of whole
cell of Anabaena , showing central
patch of granular chromatin. Bot-
tom: Detail from top left, show-
ing fine-structural features: Ch,
central region of chromatin (no lim-
iting membrane); Ca, carboxysome
(polyhedral body); Gy, glycogen
granule (cyanophycean starch); Th,
peripheral thylakoid membranes; V,
vacuole; P, thin peptidoglycan cell
wall.

Algae are relatively inaccessible and difficult to
visualise. This is the case for biofilms, where
algae are enclosed in a gelatinous matrix, and in
many cases are a relatively small component of a
very heterogeneous community of organisms. This
problem may also occur in highly radioactive envi-
ronments, where handling and visual examination
of samples can present a health hazard.

1.2.3 Molecular characterisation and identification

Although identification of algal taxa has traditionally
been based on microscopical characteristics (mor-
phology and colour), molecular techniques are being
increasingly used to characterise algal communities.
These are particularly useful where:

Diversity is being studied within species, where
strains are often distinguished in biochemical and
genetic terms.

No clear morphological characteristics are avail-
able. This has particularly been the case for unicel-
lular blue-green algae.