Types of Microorganisms in Soil
Living organisms both plants and animals, constitute an important component of soil. The pioneering investigations of a number of early microbiologists showed for the first time that the soil was not an inert static material but a medium pulsating with life. The soil is now believed to be a dynamic or rather a living system, containing a dynamic population of organisms/microorganisms. Cultivated soil has relatively more population of microorganisms than the fallow land, and the soils rich in organic matter contain much more population than sandy and eroded soils. Microbes in the soil are important to us in maintaining soil fertility / productivity, cycling of nutrient elements in the biosphere and sources of industrial products such as enzymes, antibiotics, vitamins, hormones, organic acids etc. At the same time certain soil microbes are the causal agents of human and plant diseases.
The soil organisms are broadly classified in to two groups viz soil flora and soil fauna, the detailed classification of which is as follows.
A. Soil Flora
a) Microflora: 1. Bacteria 2. Fungi, Molds, Yeast, Mushroom 3. Actinomycetes, Stretomyces 4. Algae eg. BGA, Yellow Green Algae, Golden Brown Algae.
1. Bacteria is again classified in I) Heterotrophic eg. symbiotic & non – symbiotic N2 fixers, Ammonifier, Cellulose Decomposers, Denitrifiers II) Autrotrophic eg. Nitrosomonas, Nitrobacter, Sulphur oxidizers, etc.
b) Macroflora: Roots of higher plants
B. Soil Fauna
a) Microfauna: Protozoa, Nematodes
b) Macrofauna: Earthworms. moles, ants & others.
As soil inhabit several diverse groups of microorganisms, but the most important amongst them are: bacteria, actinomycetes, fungi, algae and protozoa. The characteristics and their functions / role in the soil are described in the next topics.