The chemoautotrophs are a special class of
bacteria that can synthesize carbohydrates like the photosynthetic
bacteria do, but which obtain the energy for doing so from inorganic
reactions rather than from the sun.
Some of them obtain energy by oxidizing ammonia to
nitrite or nitrate, others convert H2S
to elemental sulfur, thiosulfate, or sulfate, and still others oxidize
Fe (II) to Fe (III).
One might think that chemosynthesis, which uses inorganic
reactions for energy, is an older mechanism than photosynthesis.
This is unlikely, since all chemoautotrophic bacteria
have well-developed respiratory chains and use O2
as an oxidant. It is more likely that these chemoautotrophs are
specially adapted forms, which found an alternative means to solar
radiation to power their carbohydrate syntheses. They can be neglected
in a search for the origin of life.
Chemoautotrophs and the inorganic materials from which they
obtain their energy
bacteria Nitrosomonas, Nitrococcus - Ammonia
o Nitrifying bacteria Nitrobacter, Nitrococcus - Nitrite
- Hydrogen Sulfide, Sulfur, Sulfate
o Ferrobacillus, Gallionella
- Ferrous Iron Salts