Microbial metabolism

Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon) it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles. Primary nutritional groups All microbial metabolisms can be arranged according to three principles:

1. How the organism obtains carbon for synthesizing cell mass: autotrophic – carbon is obtained from carbon dioxide () heterotrophic – carbon is obtained from organic compounds mixotrophic – carbon is obtained from both organic compounds and by fixing carbon dioxide
2. How the organism obtains reducing equivalents (hydrogen atoms or electrons) used either in energy conservation or in biosynthetic reactions: lithotrophic – reducing equivalents are obtained from inorganic compounds organotrophic – reducing equivalents are obtained from organic compounds
3. How the organism obtains energy for living and growing: phototrophic – energy is obtained from light chemotrophic – energy is obtained from external chemical compounds In practice, these terms are almost freely combined. Typical examples are as follows: chemolithoautotrophs obtain energy from the oxidation of inorganic compounds and carbon from the fixation of carbon dioxide. Examples: Nitrifying bacteria, sulfur-oxidizing bacteria, iron-oxidizing bacteria, Knallgas-bacteria photolithoautotrophs obtain energy from light and carbon from the fixation of carbon dioxide, using reducing equivalents from inorganic compounds. Examples: Cyanobacteria (water (H2O) as reducing equivalent = hydrogen donor), Chlorobiaceae, Chromatiaceae (hydrogen sulfide (Hydrogen sulfideH2S) as hydrogen donor), Chloroflexus (hydrogen (H2) as reducing equivalent donor) chemolithoheterotrophs obtain energy from the oxidation of inorganic compounds, but cannot fix carbon dioxide ().