Fundamentals of Microbiology

1.4.4. Protozoa

Protozoa are characterized by the features summarized below:

They are unicellular or colonical eurkaryotes. They possess protoplasmic level of organization. The body may be covered by simple plasma membrane or cuticle or pellicle. The cell wall is absent. They have various membrane bound cell organelles. Locomotory organelles may be pseudopodia (as in Amoeba) cilia (Paramecium) or flagella (Euglena). Parasitic forms do not possess any of these locomotory structures. Nutrition may be holophytic or holozoic. They may be autotrophic, heterotrophic or myxotrophic. Respiration and excretion take place through body surface. In freshwater forms contractile vacuoles serve as osmoregulatory organelles. Reproduction is generally asexual by binary or multiple fission. Sexual reproduction by conjugation is seen in some cases. Cyst formation is common in freshwater forms to overcome dry, unfavourable conditions.

Major groups of protozoa and their diseases

Group	Habitats	Common diseases	Examples
Mastigophora (Flagellates)	Freshwater; parasites of animals	Sleeping sickness Leishmaniasis	Trypanosoma Leishmania
Sarcodina (Amoebas)	Freshwater and marine; animal parasites	Amoebic dysentery	Entamoeba
Ciliophora (Ciliates)	Freshwater and marine; animal parasites	Dysentery	Paramecium
Sporozoa (Sporozoans)	Primarily animal parasites	Malaria	Plasmodium
Euglenoids (Phototrophic flagellates)	Freshwater, some marine (Also considered with algae)	---	Euglena

Other economic Significance:

Protozoa are also useful in some ways:

· Food: Protozoa provide food for insect larvae, crustaceans and worms, which are taken by large animals like fishes, lobsters, clams, and crabs.

· Symbiotic Protozoa: Certain protozoa like Trichonympha and Colonymphya etc. live in the gut of termites which help in the digestion of cellulose.

· Insect Control: Several protozoa control harmful insects by persisting their bodies.

· Sanitation: A large number of protozoa living in polluted water feed upon waste organic matters and thus purify it. Many protozoa feed upon bacteria and play important role in the sanitary betterment

· Industry: The skeletal deposits of marine protozoa (Foraminifera and Radiolaria) form oceanic ooze at the sea-bottom. These skeletal deposits are put to many uses such as filtering agents, chalk and for abrasives. The skeletal deposits in due course of time change in to the limestone rock that is used as building material.