A chemotroph is an organism that obtains energy by the redox of in their environments.
Chemoautotroph
Chemoautotrophs are
autotrophic organisms that can rely on
chemosynthesis, i.e. deriving biological energy from chemical reactions of environmental
inorganic substrates and synthesizing all necessary
from
carbon dioxide. Chemoautotrophs can use inorganic energy sources such as
hydrogen sulfide, elemental
sulfur, ferrous iron, molecular
hydrogen, and
ammonia or organic sources to produce energy. Most chemoautotrophs are
prokaryotic ,
bacteria, or
archaea that live in otherwise hostile environments (such as deep sea vents) and are the
in such
. Chemoautotrophs generally fall into several groups:
, sulfur oxidizers and reducers,
nitrification,
anammox bacteria, and
. An example of one of these prokaryotes would be
Sulfolobus. Chemolithotrophic growth can be dramatically fast, such as
Hydrogenovibrio crunogenus with a
doubling time around one hour.
The term "chemosynthesis", coined in 1897 by Wilhelm Pfeffer, originally was defined as the energy production by oxidation of inorganic substances in association with autotrophy — what would be named today as chemolithoautotrophy. Later, the term would include also the chemoorganoautotrophy, that is, it can be seen as a synonym of chemoautotrophy.
Chemoheterotroph
Chemoheterotrophs (or chemotrophic heterotrophs) are unable to fix carbon to form their own organic compounds. Chemoheterotrophs can be
chemolithoheterotrophs, utilizing inorganic electron sources such as sulfur, or, much more commonly,
chemoorganoheterotrophs, utilizing organic electron sources such as
,
, and
.
Most animals and fungi are examples of chemoheterotrophs, as are
.
Iron- and manganese-oxidizing bacteria
Iron-oxidizing bacteria are chemotrophic
bacteria that derive
energy by
redox dissolved
ferrous iron. They are known to grow and proliferate in waters containing iron concentrations as low as 0.1 mg/L. However, at least 0.3 ppm of dissolved
oxygen is needed to carry out the oxidation.
Iron has many existing roles in biology not related to redox reactions; examples include iron–sulfur proteins, hemoglobin, and coordination complexes. Iron has a widespread distribution globally and is considered one of the most abundant in the Earth's crust, soil, and sediments.
See also
Notes
1. Katrina Edwards.
Microbiology of a Sediment Pond and the Underlying Young, Cold, Hydrologically Active Ridge Flank. Woods Hole Oceanographic Institution.
2. Coupled Photochemical and Enzymatic Mn(II) Oxidation Pathways of a Planktonic Roseobacter-Like Bacterium. Colleen M. Hansel and Chris A. Francis* Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115. Received 28 September 2005. Accepted 17 February 2006.
