General Microbiology - Schlegel, H. 1987

Microbial growth
Nutritional types

The terms "heterotrophic" and "autotrophic," originally introduced to define the nutritional types of animals and plants, are inadequate for characterizing the full diversity of microbial nutritional modes. Consequently, new terms have been proposed for microorganisms, indicating their energy source, hydrogen (electron) donor, and carbon source.

Energy Sources. Depending on the mechanism by which energy is converted into a biochemical form accessible to The Cell (ATP), two primary METABOLISM/4.html">Types of Metabolism are distinguished: phototrophic and chemotrophic. Organisms capable of using electromagnetic radiation (light) as an energy source for growth are called phototrophic (photosynthetic). Phototrophs include representatives of two major groups: anaerobic phototrophic Bacteria, which do not evolve molecular oxygen, and aerobic phototrophic cyanobacteria, Algae, and green plants, which evolve oxygen in the light. In contrast, organisms that obtain energy through oxidation-reduction reactions involving nutrient substrates—regardless of whether energy conversion to a biochemical form is linked to Respiration or Fermentation—are termed chemotrophic (chemosynthetic).

Hydrogen Donors and carbon sources. All organisms that use Organic compounds as hydrogen donors are called organotrophic. They are contrasted with lithotrophic organisms, which are capable of using inorganic electron donors (H₂, NH₃, H₂S, S, СО, Fe²⁺, etc.). In microbiology, the terms "autotrophic" and "heterotrophic" are used in a narrower sense, referring strictly to THE ORIGIN OF cellular carbon: "autotrophic" microorganisms are those that can derive all or nearly all of their carbon by fixing CO₂, whereas "heterotrophic" ones obtain it primarily from organic compounds.

It is usually sufficient to indicate only the primary energy-yielding mechanism and The Nature of the hydrogen donor. Green plants, cyanobacteria, and purple sulfur bacteria are thus classified as photolithotrophs, nitrifying bacteria as chemolithotrophs, and animals along with the bulk of microorganisms as chemoorganotrophs. In specific cases, the origin of cellular carbon may also be taken into account when choosing a term.