Fundamentals of Microbiology

2.4.1 Nutritional Pattern Among Orgnaisms

Microbes are distinguished by their great metabolic diversity. All organisms, including microbes, can be classified metabolically according to their nutritional pattern—that is, their source of energy and their source of carbon.

Considering the energy source, we can generally classify organisms as phtototrophs or chemotrophs. Phototrophs use light as their primary energy source, whereas chemotrophs depend on oxidation-reduction reactions of inorganic or organic compounds for energy. For their principal carbon source, autotrophs (“self-feeders”) use carbon dioxide, and heterotrophs (feeders on others)require an organic carbon source. Autotrophs are also referred to as lithotrophs (rock eating), and heterotrophs are referred to as organotrophs.

By combining the energy and carbons sources, organisms can be classified as: Photoautotrophs, photoheterotrophs, chemoautotrophs, and chemoheterotrophs.