Photophosphorylation: Occurs only in photosynthetic cells which contain light-trapping pigments such as chlorophylls. In photosynthesis, organic molecules, especially sugars, are synthesized with the energy of light from the energy-poor building blocks CO₂ and H₂O. Photophosphorylation starts this process by converting light energy to the chemical energy of ATP and NADPH, which in turn, are used to synthesize organic molecules. As in oxidative phosphorylation, an electron transport chain is involved.

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 (CO₂)

• 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 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:

• • chemotrophic – energy is obtained from external chemical compounds

• phototrophic – energy is obtained from light.

• 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 donor), Chlorobiaceae, Chromatiaceae (hydrogen sulfide (H₂S) as reducing equivalent donor), Chloroflexus (hydrogen (H₂) as reducing equivalent donor)

• chemolithoheterotrophs obtain energy from the oxidation of inorganic compounds, but cannot fix carbon dioxide (CO₂). Examples: some Thiobacilus, some Beggiatoa, some Nitrobacter spp., Wolinella (with H₂ as reducing equivalent donor), some Knallgas-bacteria, some sulfate-reducing bacteria

• chemoorganoheterotrophs obtain energy, carbon, and reducing equivalents for biosynthetic reactions from organic compounds. Examples: most bacteria, e. g. Escherichia coli, Bacillus spp., Actinobacteria

• photoorganoheterotrophs obtain energy from light, carbon and reducing equivalents for biosynthetic reactions from organic compounds. Some species are strictly heterotrophic, many others can also fix carbon dioxide and are mixotrophic. Examples: Rhodobacter, Rhodopseudomonas, Rhodospirillum, Rhodomicrobium, Rhodocyclus, Heliobacterium, Chloroflexus (alternatively to photolithoautotrophy with hydrogen).