Fundamentals of Microbiology

4.3.1 Role of microorganisms in the cycling of elements

Decomposition and photosynthesis are the two important process of an ecosystem. Microorganisms depending on substrate specificity colonize the organic matter and decompose it. However, the organic matter serves two functions for microflora. Firstly, it provides energy for growth and secondly it provides carbon source for the formation of new cells. During this process, certain waste products are also produced by microorganisms e.g. organic acids, carbon-dioxide, methane, etc. The process of conversion of substrate to protoplasmic carbon is known as assimilation. About 20-40% substrate is assimilated and rest is released as carbon-dioxide or accumulated as waste. When the carbon assimilation occurs, the other inorganic chemicals such as nitrogen, phosphorus, potassium and sulphur are also taken up for the formation of new cells. By this process, microorganisms accumulate inorganic substances in their cells and reduce the concentration of nutrients for plants in soil. This event of accumulation of inorganic substance by the microorganisms and making the plants, nutrient-deficient is known as immobilization. Microorganisms of different groups colonize the substrate depending upon its chemical composition. Thus microbial succession occurs on the decomposing material till it fully disappears in elemental forms. The events of sequential appearance of microorganisms on a substrate with respect to time are called succession.