Environmental Microbiology of Aquatic and Waste Systems

4.1 Taxonomy of Microorganisms in Aquatic Environments 79

Protozoa are classified in many ways, primarily on
morphological characteristics, and the one adopted
here groups them into five: Mastigophora, Sarcodina,
Ciliata, Sporozoa, and Suctoria.

1. Flagellata (Mastigophora)
   These possess flagella and are subdivided into “phyto­
   flagellata” and “zooflagellata,” depending on whether
   they are plant­like (with chlorophyll) or animal­like
   (without chlorophyll). They usually multiply by lon­
   gitudinal binary fission. Many flagellates are able to
   feed autotrophically as well as heterotrophically, and
   are important primary producers in lakes and oceans;
   yet, they can also feed like animals, ingesting or
   absorbing food synthesized by other organisms.
   Many are free­living, but some are parasitic.
   Examples of parasitic Mastigophora are Trypano­
   soma gambiense and T. rhodesiense which cause
   African sleeping sickness and is transmitted by
   tsetse flies. T. cruzi is the cause of Chagas’ disease,
   prevalent in South and Central America, which
   affects the nervous system and heart; it is transmit­
   ted by the bite of assassin bugs. Giardiasis is caused
   by the mastigophoran Giardia lamblia.


2. Rhizopoda (Sarcodina)
   These Protozoa use pseudopodia (false feet) for
   locomotion and for catching preys. Members of the
   group Sarcodina move by pseudopodia; although,
   flagella may be present in the reproductive stages.
   Cytoplasmic streaming assists movement. Asexual
   reproduction occurs by fission of the cell.
   Sarcodina includes two marine groups known as
   foraminiferans and radiolarians. Both groups were
   present on earth when the oil fields were in formative
   stages, and marine geologists use them as potential
   markers for oil fields. Some amoebae live in shells

from which the pseudopodia are extruded. Some

members of the group such as Entamoeba histolytica,

are pathogenic, causing amoebic dysentery in humans.

This organism can cause painful lesions of the intes­

tine and is contracted in polluted water (Fig. 4.2 1 ).

3. Ciliata
   Ciliates possess cilia (short and highly coordinated
   flagellae), a somatic (macro) nucleus, and genetic
   (micro) nucleus, and a contractile vacuole is usually
   present. They move by means of cilia. Conjugation
   may be used for sexual reproduction and binary fis­
   sion also occurs. The distinctive rows of cilia vibrate
   in synchrony and propel the organism in one direc­
   tion. One of the best known members of the group
   is Paramecium; another of the free­living members
   of this group, is Tetrahymena.
   Ciliates form an extremely large group are dis­
   tinguished by the possession of cilia, two different
   types of nuclei and transverse fission of the organ­
   ism when it divides, unlike flagellates and sarcodina
   which divide longitudinally.


4. Sporozoa
   Members of the group Sporozoa form spores at one
   stage in their life cycle. Sporozoa are endoparasites
   which have spores. Most of them spend at least part
   of their life­cycle inside a host cell. Reproduction is
   a complex phenomenon in this group. Members of
   the group display no means of locomotion in the
   adult form. Their motile stages move by bending,
   creeping, and gliding and usually have an apical
   complex at their anterior end which help them pen­
   etrate their hosts. The group includes Plasmodium,
   the agent of malaria, Toxoplasma, the agent of toxo­
   plasmosis, and Pneumocystis carinii, the cause of a
   serious pneumonia in AIDS patients.

Red algae

Diplomads

(Giardia)

Microsporidia

Tricho

monads

Trypano

somes

Euglenoids

Slime

moulds

Brown

alage

Diatoms

Oomycetes

Fungi

Plants

Green algae

Animals

Ciliates

Dinofla

gellates

Fig. 4.20 Phylogenetic
tree among the Eukarya
(Redrawn from Ciccarelli
et al. 2006 )