Environmental Microbiology of Aquatic and Waste Systems

82 4 Taxonomy, Physiology, and Ecology of Aquatic Microorganisms

Sporangium

producing

zoospores

zoospore Oogonium with

antheridium

antheridium

oogonium

tinsel

flagellum

whiplash

flagellum

Fig. 4.23 Reproductive structures in aquatic fungi (From Rossman and Palm 2006. With permission)

Table 4.8 Properties of oomycetes and other (“true”) fungi (Modified from Rossman and Palm 2006. With permission)

Character Oomycota True Fungi
Sexual reproduction Heterogametangia. Fertilization of
oospheres by nuclei from antheridia
forming oospores

Oospores not produced; sexual
reproduction results in zygospores,
ascospores, or basidiospores
Nuclear state of vegetative mycelium Diploid Haploid or dikaryotic
Cell wall composition Beta glucans, cellulose Chitin. Cellulose rarely present
Type of flagella on zoospores, if produced Heterokont, of two types, one whiplash,
directed posteriorly, the other fibrous,
ciliated, directed anteriorly

If flagellum produced, usually of only

one type: posterior, whiplash

Mitochondria With tubular cristae With flattened cristae

(e) Deutromycetes (Deuteromycota) or fungi imper fecti
These are fungi whose perfect or sexual stages have
not been discovered. Some of the best examples are
Penicillin spp. (with broom­like structures) and
Aspergillus spp. (with club­like structures).

4.1.6.3 Algae

Algae are photosynthetic eukaryotic organisms which
lack the structures of vascular plants. Many authors
classify them as microorganisms, but they are highly
variable in size and range from microscopic sizes to
the brown algae which could be up to 70 m long
(Trainor 1978 ; Sze 1986 ) (Fig. 4.24).

Taxonomy of Algae
The classification of the algae is based on the
following:
(a) Pigmentation
The various kinds of pigments in the algae, as well as
the overall color of the alga, are used in classifying
the organisms. All of the groups contain the follow­
ing pigments which are soluble in organic solvents:
Chlorophylls and several carotenoids, which include
carotenes and xanthophylls. Chlorophylls “a” and
“b,” alpha or beta carotene, and some xanthophylls
are common. The water soluble phycobiliproteins

(phycobilins) are found in blue­green algae, red

algae, and a small group of flagellates.

(b) The reserve compound

Reserve food material is usually stored within the

cell and frequently within the plastid in which

photosynthesis occurred. Starch, starchlike com­

pounds, fats, or oils are the most common forms.

(c) The nature of the zoospores

Some organisms are motile during much of their

lives, whereas other genera lack motility, or any

motile reproductive stages. Adult algae are usually

nonmotile; often, however, some reproductive

stages (zoospores) are motile. The overall shape of

the zoospores, the shape, number, and the insertion

position of the flagella, and the presence or absence

of hairs on the flagella are diagnostic (Fig. 4.24;

Table 4. 9 ).

(d) Wall composition

The cell wall may be a simple outer covering around

the protoplast or an elaborately ornamented struc­

ture. The materials found in algal walls are cellulose,

xylans, mannans, sulfated polysaccharides, alginic

acid, protein, silicon dioxide, and calcium carbonate

(e) Gross morphology of the alga

The overall shape of the alga is diagnostic.

The various groups of algae are given in the Table 4. 9.