Protozoa

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Protozoa

Protozoa

Soil protozoa are unicellular. In general they lack chlorophyll barring few exceptions. They are characterized by a cyst stage in their life cycle which can help the species to withstand adverse soil conditions.

Barring a few genera which reproduce sexually by fusion of cells, the rest of them reproduce asexually by fission. The flagellated protozoans belonging to the class Mastigophora are predominant in soil.

Important genera are Allantion, Bodo, Cercobodo, Cercomonas, Entosiphon, Heteromita, Monas, Oikomonas, Sainouran, Spiromonas, Spongomonas and Tetramitus. Unlike the flagellates which move with the help of their flagella numbering

A. Bodo	B. Cercobodo	C. Tetramitus	D. Naegleria	E. Euglypha

F. Biomyxa	G. Balantiophorus	H. Colpoda	I. Uroleptus

up to four, there are protozoa in soil which move with the help of extrusions of protoplasm known as false feet or pseudopodia. The protoplasm may be naked or as in some genera encased in shells. Important soil inhabitants of this class known as Sarcodina are Amoeba, Biomyxa, Difflugia, Euglypha, Hartmanella, Lecythium, Naegleria, Nuclearia and Trinema.

A third group of soil protozoa belong to the class Ciliata. They are distinguished by the possession of minute hairs called cilia around their bodies which help in locomotion. Important genera of this class are Balantiophorus, Colpidium, Colpoda, Enchelys, Gastrostyla, Halteria, Oxytricha, Pleurotricha, Uroleptus and Vorticella.

Apart from the classes Mastigophora, Sarcodina and Ciliata which are soil inhabitants, the phylum protozoa has two more classes (Suctoria and Sporozoa) which are not considered here.

Protozoa live in soil at the expense of bacteria of the genera Aerobacter, Agrobacterium, Bacillus, Escherichia, Micrococcus and Pseudomonas by ingesting them into their protoplasm. The protozoans prefer certain species of bacteria for their nutrition.

In fact, Aerobacter cultures are recommended as a food base for isolation and enumeration of soil protozoans. When the food base (bacteria) diminishes in soils, the protozoa get encysted (form cysts) for survival against the harmful action of high temperature, drought, application of pesticides, etc.

Protozoa are abundant in the upper layer of the soil and their numbers are directly dependent on bacterial population. Application of organic manures increases the number of soil protozoans which is again a reflection on the corresponding increase in the bacterial flora due to the application of organic matter.

Owing to inadequate studies on soil protozoa, it is difficult to define the role of individual factors such as pH and temperature on protozoan population in soil.

Nevertheless, it is clear that protozoa are abundant in soil and their main function is to regulate the number of bacteria.

Nothing is known about the associative effects of protozoa with other soil microorganisms for the simple reason that very few workers have been attracted to this field, more so, because isolation and quantification of soil protozoans involve time-consuming procedures.

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