Autotrophic Bacteria: These microscopic organisms can combine their own food from inorganic substances, as green plants do. They get their carbon from carbon dioxide. The hydrogen expected to decrease carbon to natural structure originates from sources, for example, climatic H2, H2S, or NH3. Heterotrophic Bacteria: The greater part of the microorganisms can't integrate their own natural food. They subsequently rely upon outer natural materials. They require, in any event, one natural compound as a wellspring of carbon for their development and vitality. Such microorganisms are heterotrophic microscopic organisms. Heterotrophic microscopic organisms are of three types­: Parasites, Saprotrophs, and Symbionts.