Blue Green Algae, Protozoa And Fungi

Blue-green algae:

It is found in the habitat where moisture adequate and light is accessible. They are widely distributed in nature in terrestrial fresh water and marine habitats. They are more tolerates to environmental extreme than other algae and dominant oxygenic phototropic organism in hot springs saline lakes and other extreme environment. Many members are found on the surface of rocks or soils and even within the rocks. A few are symbionts of liverworts ferns and cycads and as the phototropic component of lichens. They belong to the class cyanophycean. The pigments are distributed throughout the cytoplasm. The nucleus lacks the clear morphological organization. They possess the ability to divide by fission. Their characteristic blue-green color is due to the presence of blue pigment phycocyanin in addition to chlorophyll A and carotenoids. Some cyanobacteria produced a red phycobilin i.e phycoerythrin. They tolerate a wide range of temperature and may even be found in hot springs. They prefer neutral to alkaline environment i.e pH 7-10 and are usually absence in the environment of pH below 5.2 but are frequently present in the neutral or calcareous land. They are in permanent pasture cultivated fields and manure land. They are present in a definite population in highly arid habitats also. They are found predominantly at the liquid surface of water-logged rice field if the pH is above 6 and the phosphorous level is high. Blue-green algae capable of making used of nitrogen make a large proportion of the microbial population of in arid areas and areas denuded by volcanoes. These algae help the soil to gain organic forms of carbon and nitrogen from the atmosphere. Therefore, they are important members of soil micro flora. Blue-green algae are the first oxygen evolving microorganism on the earth and are responsible for the oxygenating the atmosphere. They are photoautotrophic and have the capacity to utilized simple inorganic compound. Molecular oxygen is evolved in their metabolism and this helps in the evolution of prokaryotes that could use oxygen for respiration. They are phylogenetically related to gram-positive bacteria. Morphologically, there are five types of blue-green algae. They are:

1. Unicellular: eg Gloeothece species.
2. Colonial : eg . Myxosarcina species.
3. Filamentous: eg Oscillatorria species.
4. Filamentous heterocystous: eg Nostoc species, Anabaena.
5. Filamentous branching: eg. Fischerelle species.

The cells range in size from 0.5 to 1-micron meter in diameter to cells as large as 40-micron meter in diameter as in O princess. Gas vesicles are seen in the cytoplasm which helps to regulate cell buoyancy so that it remains in such a position in the water column where light is optimum for synthesis.

Protozoa:

It contains primitive unicellular organism ranging in size from several microns to 1 or more cm. They are microscopic and devoid of chlorophyll. The life cycle consists of an active phase in which the animals feeds to multiply and the resting or cyst stage where the cell secrete thick coatings around itself. In the cyst stage, it can tolerate adverse environmental condition and persist for many years. Reproduction is usually by fission or longitudinal division. Some can undergo sexual reproduction in which two cells fused their nuclei unite.Genetic materials exchange and two new individuals emerge on the basis of locomotion. They are divided into five classes:

1. Mastigophora or Flagellates: Which are motile by flagella, have one to four flagella small five to 20 microns in length. eg Allantoin, Bodo.
2. Sarcodina o r Rhizopus: which possess pseudopodia. They move by temporary protoplasmic extrusion. No rigid exterior surface. Changes its shape frequently as it senses forth and withdraws pseudopodia. Eg Amoeba, Biomyxa.
3. Ciliata: Which bears cilia through the entire active stage. Cilia is short and numerous. Several thousand may be found in the single individual. Size 10 to 18 micron. Eg. vorticella, caladium.
4. Victoria: They bears cilia only at the young stage.
5. Sporozoa: They are parasitic without special locomotory organ.

Photosynthetic protozoa synthesize their protoplasm from CO₂ Using energy derived from sunlight. Most depend on organic matter and obtained nutrients from soluble organic and inorganic substance or by directly feeding upon microbial cells. Cyst appears when nutrients supply is low and other unsuitable condition. Cysts are more tolerate to harmful chemicals, acids germicides, and high temperature than the vegetative cells and remain viable even in dry season. Therefore, they are more protective than serving reproductive system. protozoans are found mostly near the surface of the soil usually in upper 6 inches. They are relatively scarce in sub soil. The population is most dense where bacteria are numerous. Applied organic matter in the soil also increases the number of protozoa and adequate water supply is essential for the physiological activity and lateral and vertical movement. Flagellates are tolerant of low moisture and can develop in drier condition. ciliates are abundant only when moisture status is high. When the water supply is too low,the protozoans encyst and remains as the cyst. Most are aerobic but some can grow at the low level of O₂ or in complete anaerobic condition. They usually show no sensitivity to pH. The range may vary from 3.5 to 9. Optimum pH is 6-8. They do not have specific temperature requirements but extreme warm is detrimental. They favor cool and damp environment.

Fungi:

Fungi account for largest part of the total microbial protoplasm in the well-aerated soil. The dominance in mass is due to the large diameter and extensive network of the filaments. They are the major agent of decay in the acidic soil. The filaments are usually not visible to the nacked eye but can be seen by the direct examination of soil by Rossi-colony buried slide technique. Results of such investigation have shown that fertile soil may contain 10-100 m of active filaments per gram of soil. Fungi possess four filamentous mycelium networks of individual hyphal strands. The mycelium may be sub divided into individuals cells by cross walls or septa but many fungi are nonseptate. The hyphae of nonseptate fungi are continuous and multinucleated. Hyphae may be vegetative or fertile. The fertile filaments produce sexual or asexual spores. Conidia or asexual spores are abundant and wide spreads. The sexual spores are less common. Mycelium is usually colorless but the asexual spores are strikingly colored. They are heterotropic in nutrition. They cannot be obtained energy from sunlight or oxidation of inorganic substance. They derive their nutrition from the oxidizable carbonaceous substance. The addition of crops residues green manure and other energy-rich carbonaceous materials into the soil increases the soil fungal population. Hydrogen concentration is an important factor for controlling the fungal population in the soil. Molds can develop over a wide pH range from highly acidic to highly alkaline extremes they can grow at PH value 2-3 in laboratory medium and some are active at pH 9 or more. The area with low pH is highly dominated by fungi because bacteria and actinomycetes are not found in low pH. Soil water has a direct effect on abundance and function of fungi. Their capacity for catalyzing chemical change is poor or absent when the water supply is low.

Gilman's Authoritative monograph of soil fungi:

Class I : Fungi imperfecti

1. Moniliaceae: Conidiophores scattered in loose irregular masses conidia and conidiophores either clear or bright in color. eg. Aspergillus, Cephalosporium, Monilia, Penicillium, Trichoderma.
2. Dermatiaceae: Conidiophores scattered in loose irregular masses conidia and conidiophores are dark in color. eg. Alternaria, Cladosporium, pullularia.
3. Tuberculariaceae: Conidiophores gathered into a sporodochium. eg. Fusarium, Cylinderocarpon.

Class II : Phycomycetes

1. Mucorales: Sporangia containing asexual spores are cylindrical zygospore formed. eg.Mucur, Rhizopus, Absidia.
2. Peronosporales: Asexual spores mortile, mycellium well develop having single oospore. eg. Pythium.

Class III : Ascomycetes : Ascospores formed in asci filaments septate. eg. Chaetomium.

Class IV : Sterilia : Conidia not formed. eg Rhizoctonia.

Spring and autumn season is beneficial for fungal growth. It is because carbonaceous nutrients are abundant in soil in the form of dying roots and plowed under crop residues in this season. They play the main role in rotting of woody tissue in lignin decomposition and in the mycorrhizal association. Since fungi have no chlorophyll. They must obtain carbon for cell synthesis from preformed organic molecules. They utilize carbon source such as hexose, pentose, organic acid, disaccharides, starch, cellulose, fat, lignin etc. Fungi also show the predatory mode of nutrition.The utilization of proteinous substances causes the formation of ammonium and simple nitrogen compound in the soil. Saprophytic fungi invade the living tissue and cause the differents plants disease.

References:

1. Alexander M (1961). Introduction to soil microbiology, Academic press.
2. Rangaswami G and Bagyaraja PT (1993). Agriculture Microbiology (second edition), Prentice Hall of India.