Nematodes derive nutrients for their growth and reproduction from the cell conВtents and cytoplasm of protozoa, bacteria, fungi, etc. In recent years the ecology of nematodes has been greatly advanced. Until the role of nematodes in soil was understood nematology was in infancy stage. 30.2 : Microbial world of soil environment showing possible interactions between microbes and energy substrate, microbes and physical factors and between the microbes themselves (energy substrates include inorganic chemicals, dead organics and living plant root and soil fauna) 6. Interaction of soil-amoebae with fungal hyphae has been discussed in section Microbial Interactions.ДЇig. However, the number of protozoa can be correlated with plant root growth and indirectly with status of soil nutrients. The role of soil protozoa is predatory, as these eat upon bacteria and thereby regulate their population. The population of each group is 10 3 per gram wet soil. In moist soil most of the members of microfauna remain in encysted form. However, there role has not been clearly understood. Bacteriophages:Д«acteriophages as well as plant and animal viruses have been observed in the soil. The important members of actinomycetes are: Actinomyces, Actinoplanes, Micromonospora, Microbispora, Nocardia, Streptomyces, Thermoactinomyces, etc. Its luxurient growth is favoured by neutral or alkaline pH (6.0 to 8.0).

The most limiting factor is the pH which governs their abundance in soil. In temperate zones the number of actinomycetes ranges from 10 5 to 10 8 per gram soil. Population of actinomycetes in soil remains greater in grass land and pasteur soil than in the cultivated land. However, the earthy odour of newly wetted soils has been found to be a volatile growth product of actinomycetes. They are Gram-positive and release antibiotic substances. Example of some of soil bacteria is Agrobacterium, Arthrobacter, Bacillus, Alcaligens, Clostridium, Corynebacterium, Erwinia, Nitrosomonas, Nitrobacter, Pseudomonas, Rhizobium, Thiobacillus, etc.ДЄctinomycetes share the characters of both bacteria and fungi, and they are commonly known as вЂњray-fungiвЂќ because of their close affinity with fungi. Moreover, they play a maВjor role in organic matter decomposition, bio-trans- formation, biogas producВtion, nitrogen fixation, etc. This may be due to polymer formation, motility, surface changes, and life cycle of bacteria involved.Д«acteria do not occur freely in the soil solution but are closely attached to soil particles or embedded in organic matВter even after adding the dispersing agents bacteria are not completely disВlodged from the soil parВticles and distributed in susВpension as individual cell.

The inner region of soil aggregates contained higher level of Gram-negative bacteria, while the outer region contained higher level of Gram-positive bacteria. They are found in high number in cultivated than virgin land, maximum in rhizosphere and less in non-rhizosphere soil possibly due to aeration and nutrient availability. Moreover, the number and types of bacteria are influenced by soil types and their microenvironment, organic matter, cultivation practices, etc.

Insidia bacteria soil bacteria