Bacteria, like all living cells, require energy and nutrients to build proteins and structural membranes and drive biochemical processes. Bacteria require sources of carbon, nitrogen, phosphorous, iron and a large number of other minerals. Carbon, nitrogen and water are used in highest quantities. The nutritional requirements for bacteria can be grouped according to the carbon source and the energy source.
Autotrophs are bacteria which obtain their nutrition from inorganic compounds. Carbon dioxide is typically the sole source of cellular carbon. Autotrophs will use hydrogen sulfide, ammonia or hydrogen gas to reduce carbon into necessary sugars. Nitrifying bacteria, which oxidize ammonia to create nitrites and nitrates, are an example of bacteria which use autotrophic nutrition.
Bacteria that require organic sources of carbon such as sugars, fats and amino acids are termed heterotrophs. Saprophytic bacteria are an example. They attain their nutrition from dead organic matter. Using enzymes, these bacteria will breakd own complex compounds and use the nutrients to release energy. Saprophytic bacteria are essentially decomposers and play an important role in ecosystem by releasing simpler products which plants and animals can use.
Phototrophic bacteria absorb light energy, then utilize this in photosynthesis to create cellular energy. There are two types of phototrophs; those which do not produce oxygen as a byproduct are termed anaerobic phototrophs, while those which do produce oxygen are termed aerobic phototrophs. Both autotrophs and heterotrophs can be phototrophs. Cyanobacteria are an example of bacteria which execute photoautotrophic nutrition.
These bacteria obtain chemical energy from their surroundings and convert it into adenosine triphosphate (ATP) for cellular use. Chemotrophs attain energy from oxidation-reduction reactions of inorganic compounds such ammonia, hydrogen sulfide and iron. For instance, sulfur bacteria is a chemoautotroph which produces energy by oxidizing hydrogen sulfide into sulfur and water.
Lithotrophs are bacteria which use reduced inorganic compounds as the electron donor (H-donor) in anaerobic or aerobic respiration.