Protozoa: Economic Importance | Zoology Optional Notes for UPSC PDF Download

Protozoa encompass minute, single-celled creatures that have successfully colonized a wide range of ecological niches on Earth. These organisms can be found in water, in the damp layers of soil, in the air, and even as symbionts or parasites within both animal and plant hosts. Given that humans are a biological species, they are inevitably affected by these microorganisms.
Some of these protozoa prove to be beneficial as they contribute to sanitation efforts, serve as a source of food, play a role in the formation of oceanic sediment, and aid in the investigation of various biological processes. However, many of these microorganisms pose a threat to human health by causing a variety of serious diseases in humans and domesticated animals such as cattle, poultry, and fish.

Beneficial Protozoa

Some protozoa are of great importance for mankind and other animals.

According to their utility they can be classified into following categories:

(a) Helpful in Sanitation: There are some putrefying bacteria found in polluted water, living on various waste organic substances which they decompose. Numerous holozoic protozoa, however, feed on such bacteria, thus helping indirectly purification of water. These protozoa play an important part in the sanitary betterment and improvement of the modern civilized world in keeping water safe for drinking purpose.

(b) Planktonic Protozoa as Food: Protozoa floating in the plankton of the sea form one of the first links in the numerous and complicated food chains that exist in the oceans of the world. Clams and young fish feed extensively on aquatic insect larvae, small crustaceans, worms, etc., all of which take protozoa as food. Thus, protozoa directly or indirectly form the food of fish, clams and other animals, which in their turn are consumed by man. Diatoms and dinoflagellates, forming a large part of plankton, are the world’s original synthesizers of organic foodstuffs producing nearly 90% of all the organic food. According to laboratory researches, they can produce eighty times as much food as the most efficient protein producing crops now grown by man.
For example, a single acre of land can annually produce 40 tons of these micro­organisms as compared with half ton of soya-beans or two hundred fifty pounds of beef. Naturally, this tremendous food-manufacturing potential of planktonic protozoa promises great possibilities for the world’s future food requirements.

(c) Commensal Protozoa: The commensal protozoans are those which live on or in body of other animals (hosts) and derive some benefit from the relationship.

They may be of following two types:

• Ectocommensal Protozoa: The ectocommensal protozoa live on the surface of the body of host. Various ciliates and suctorians lead an Ectocommensal life on molluscs, arthropods, fishes, frogs, etc. The bodies of such simply serve as substratum for these ectocommensals. 
• Endocommensal Protozoa: The endocommensal protozoans live inside the body of animals. For example, Trichomonas, Giardia, etc., (Mastigophora), Entamoeba coli (Rhizopoda) Nyctotherus, Balantidium and Opalina (Ciliata), live as endocommensals within the alimentary canal of man, frogs, cockroaches and others. They feed on bacteria and so have beneficial effect.

(d) Symbiotic Protozoa: Some protozoans are found in symbiotic relationship with other organisms. This association is usually beneficial to both the individuals. The two partners become so dependent on each other that one cannot get along without the other and their separation results in the death of both. Most outstanding examples of symbionts among the Protozoa are several intestinal flagellates (Trichonympha, Colonympha etc.) of termites and wood roaches. According to Cleveland, these flagellates are extremely vital for the very existence of their hosts. They digest cellulose converting it into soluble glycogen substances for the use of the hosts.

(e) Zoological Importance of Protozoa: The protozoans have been found as an ideal group of animals for cytological, cytochemical, physiological, biochemical, and genetical studies, because of small size, simple organization, quick reproduction and easy availability. 

(f) Commercial Uses of Protozoan Skeletons: The skeletons of dead foraminifera and radio laria sink to the sea bottom and form the oceanic ooze. They solidify and convert into rock. Such sort of strata of oceanic ooze is white chalk cliffs of Dover and England, and stone between Paris, Cairo and North America. A large number of Paris buildings are built of the limestone which is exclusively composed of the shells of genus Hiliolina. Similarly pyramids of Egypt are constructed by lime­stone deposits of Nummulite shells. Sometimes, the skeletal deposits are used as decorative agents and as abrasives. 

(g) Oceanic Ooze and Fossil Protozoa: The tiny skeletons of dead pelagic Foraminifera, Radiolaria and Heliozoa sink to the sea bottom forming the soft mud or oceanic ooze. These tiny skeletons are made of silica or calcium carbonate. Over countless millions of years these skeletons, deposited on the floor of the ocean, became solid and fossilized and converted into some important sedimentary rock strata found all over the world. These have been put to various commercial uses, such as filtering agents, abrasives, chalk, building stones, etc. The white chalk cliffs of Dover, England and the limestone beds of Paris, Cairo and North America are composed almost exclusively of the fossil Foraminifera. Most of the buildings of Paris are made of limestone composed almost exclusively of the shells of the foraminiferan genus Miliolina. Similarly, the great pyramids of Egypt were carved from the limestone deposits by tests of an early Tertian foraminiferan, Nummulites. The radiolarian fossils are abundant in the hard rocks of the nature of sandstone, quartz or flint used in the manufacture of glass. They also constitute a part of the Tripoli Stone, which is used in abrasive powders of polishing metals. The aborigines of America eagerly sought flint or chert to convert them into arrow points and knives. The skeleton remains of radiolarians and foraminiferans often occur in association with oil deposits and provide help in locating this precious fluid. Therefore, the petroleum geologists carefully study them, obtained in drilling test wells, to identify the oil-bearing strata.

Harmful Protozoa

Almost all harmful protozoans are found as parasites in both plants and animals including man and causes various fatal and dangerous diseases.

• Pathogenic Protozoa: Some Protozoa cause diseases in man as well as animals and these are termed pathogenic Protozoa. They occur in all classes of protozoa. 
• Pathogenic Sarcodines: These are two common genera of parasitic amoebae, Entamoeba and Endamoeba, which live in the intestine of man and of other animals. Only two species of Entamoeba are known to be seriously pathogenic E. histolytica of man and other mammals and E. invadens of reptiles. E. histolytica is responsible for amoebic dysentery or amoeliasis in man, which occurs in about 130% Indian population. 
• Pathogenic Sporozoans: The class Sporozoa is exclusively of parasitic forms. Though most of sporozoans are harmless, yet some genera like Plasmodium, Eimeria, Isopora and Babesia include pathogenic species. Four species of Plasmodium, namely P. vivax, P. malariae, P. ovale and P. falciparum cause malaria in man. P.cynanomolgi in monkeys, by P. verghei in trees and rats and by P. gallinaceum in jungle fowl of Asia. 
• Pathogenic species of Eimeria cause coccidiosis in chickens and rabbits. E. canis in dogs, E. felina in cats, E. bovis in cattle and E. intricate in sheep and goats. Isospora, is intestinal parasites of man and other animals. Species of Babesia are intra-erythrocytic parasites of various verebrates e.g. Babesia bigemina of cattle causes the lethal haemoglobinuric fever, red water fever or Taxas fever. B. equi in horses, B. rodhani in rodents, B. felis in cats, B. motasi in goats, cause malignant jaundice, anaemia and fever in their specific hosts. 
• Pathogenic Ciliates: Balantidium coli are the only important ciliate pathogenic parasite. It is found in the intestine of man and often in frogs. 
• Pathogenic Flagellates: Pathogenic parasitic flagellates include the genera Leishmania, Trypanosoma, Histomonas, Trichomonas and Giardia. Three pathogenic species of Leishmania have been known to cause severe disease in man, causing Kala-azar, and L. braziliensis causes infection of nasopharynx and skin lesion. 
• These are transmitted by sandflies of the genus Phlebotomus. Another parasitic species of Trypanosoma in mammals cause worst diseases i.e. fatal African sleeping sickness. T. Rhodesiense, is other common pathogenic species. Of the parasitic species of Trichomonas, is the causative organism of vaginal trichomoniasis or vaginitis in human females. T. foetus causes trichomoniasis of cattle in U.S., and T. gallinae is pathogenic in doves, pigeons turkeys and chickens.

Water Pollution

Whereas some protozoa are helpful in water sanitation, others become responsible for water contamination or pollution. 

• The protozoa of faecal origin belong to this latter category. Some free-living protozoa (e.g. Uroglenopsis) also pollute water by producing aromatic and oily secretions with objectionable odours, which render water unfit for human consumption. 
• Some bioluminescent dinoflagellates, such as Noctiluca Gymnodinium and Gonyaulax, living in sea, sometimes multiply so extensively as to turn the water red with their bodies. The phenomenon is known as blooming and is the cause of “red tides”, often experienced in the sea. Outbreaks of this “red water” often give a foul and disagreeable odour to the ocean water. 
• Large concentrations of these flagellate protozoans may even lead to destruction of fish and poisoning of edible mollusks, such as clams, oysters and mussels, etc., making them unfit for human consumption.

Soil Protozoa

Several species of protozoa, present in large numbers in soil, feed upon the nitrifying bacteria, and thus decline their activity and consequently tend to decrease the amount of nitrogen given to soil by the nitrifying bacteria.