Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments.[1] These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototrophs, which use solar energy. Chemotrophs can be either autotrophic or heterotrophic. Chemotrophs are found in ocean floors where sunlight cannot reach them because they are not dependent on solar energy. Ocean floors often contain underwater volcanos that can provide heat as a substitute for sunlight's warmth.

Blacksmoker in Atlantic Ocean
A black smoker in the Atlantic Ocean providing energy and nutrients


Chemoautotrophs (or chemotrophic autotroph) (Greek: Chemo (χημία) = chemical, auto (αὐτός) = self, troph (τροφιά) = nourishment), in addition to deriving energy from chemical reactions, synthesize all necessary organic compounds from carbon dioxide. Chemoautotrophs use inorganic energy sources such as hydrogen sulfide, elemental sulfur, ferrous iron, molecular hydrogen, and ammonia. Most chemoautotrophs are extremophiles, bacteria or archaea that live in hostile environments (such as deep sea vents) and are the primary producers in such ecosystems. Chemoautotrophs generally fall into several groups: methanogens, halophiles, sulfur oxidizers and reducers, nitrifiers, anammox bacteria, and thermoacidophiles. 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.[2][3]

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.[4][5]


Chemoheterotrophs (or chemotrophic heterotrophs) (Gr: Chemo (χημία) = chemical, hetero (ἕτερος) = (an)other, troph (τροφιά) = nourishment) are unable to fix carbon to form their own organic compounds. Chemoheterotrophs can be chemolithoheterotrophs, utilizing inorganic energy sources such as sulfur or chemoorganoheterotrophs, utilizing organic energy sources such as carbohydrates, lipids, and proteins.[6][7][8][9] Most animals and fungi are examples of chemoheterotrophs.

Iron- and manganese-oxidizing bacteria

In the deep oceans, iron-oxidizing bacteria derive their energy needs by oxidizing ferrous iron (Fe2+) to ferric iron (Fe3+). The electron conserved from this reaction reduces the respiratory chain and can be thus used in the synthesis of ATP by forward electron transport or NADH by reverse electron transport, replacing or augmenting traditional phototrophism.

  • In general, iron-oxidizing bacteria can exist only in areas with high ferrous iron concentrations, such as new lava beds or areas of hydrothermal activity. Most of the ocean is devoid of ferrous iron, due to both the oxidative effect of dissolved oxygen in the water and the tendency of bacteria to take up the iron.
  • Lava beds supply bacteria with ferrous iron straight from the Earth's mantle, but only newly formed igneous rocks have high enough levels of ferrous iron. In addition, because oxygen is necessary for the reaction, these bacteria are much more common in the upper ocean, where oxygen is more abundant.

Manganese-oxidizing bacteria also make use of igneous lava rocks in much the same way; by oxidizing manganous manganese (Mn2+) into manganic (Mn4+) manganese. Manganese is more scarce than iron oceanic crust, but is much easier for bacteria to extract from igneous glass. In addition, each manganese oxidation donates two electrons to the cell versus one for each iron oxidation, though the amount of ATP or NADH that can be synthesised in couple to these reactions varies with pH and specific reaction thermodynamics in terms of how much of a Gibbs free energy change there is during the oxidation reactions versus the energy change required for the formation of ATP or NADH, all of which vary with concentration, pH etc. Much still remains unknown about manganese-oxidizing bacteria because they have not been cultured and documented to any great extent.


AutoHeteroTrophs flowchart

See also


  2. ^ Dobrinski, K. P. (2005). "The Carbon-Concentrating Mechanism of the Hydrothermal Vent Chemolithoautotroph Thiomicrospira crunogena". Journal of Bacteriology. 187 (16): 5761–5766. doi:10.1128/JB.187.16.5761-5766.2005. PMC 1196061. PMID 16077123.
  3. ^ Rich Boden, Kathleen M. Scott, J. Williams, S. Russel, K. Antonen, Alexander W. Rae, Lee P. Hutt (June 2017). "An evaluation of Thiomicrospira, Hydrogenovibrio and Thioalkalimicrobium: reclassification of four species of Thiomicrospira to each Thiomicrorhabdus gen. nov. and Hydrogenovibrio, and reclassification of all four species of Thioalkalimicrobium to Thiomicrospira". International Journal of Systematic and Evolutionary Microbiology. 67 (5): 1140–1151. doi:10.1099/ijsem.0.001855. PMID 28581925.CS1 maint: Multiple names: authors list (link)




Cold seep

A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. Cold does not mean that the temperature of the seepage is lower than that of the surrounding sea water. On the contrary, its temperature is often slightly higher. The "cold" is relative to the very warm (at least 60 °C or 140 °F) conditions of a hydrothermal vent. Cold seeps constitute a biome supporting several endemic species.





An extremotroph (from Latin extremus meaning "extreme" and Greek troph (τροφ) meaning "food") is an organism that feeds on matter that is not typically considered to be food to most life on Earth. "These anthropocentric definitions that we make of extremophily and extremotrophy focus on a single environmental extreme but many extremophiles may fall into multiple categories, for example, organisms living inside hot rocks deep under the Earth's surface."



Precambrian body plans

Until the late 1950s, the Precambrian era was not believed to have hosted multicellular organisms. However, with radiometric dating techniques, it has been found that fossils initially found in the Ediacara Hills in Southern Australia date back to the late Precambrian era. These fossils are body impressions of organisms shaped like disks, fronds and some with ribbon patterns that were most likely tentacles.

These are the earliest multicellular organisms in Earth's history, despite the fact that unicellularity had been around for a long time before that. The requirements for multicellularity were embedded in the genes of some of these cells, specifically choanoflagellates. These are thought to be the precursors for all multicellular organisms. They are highly related to sponges (Porifera), which are the simplest multicellular organisms.

In order to understand the transition to multicellularity during the Precambrian, it is important to look at the requirements for multicellularity—both biological and environmental.



Thermus aquaticus


Food webs
Example webs
Ecology: Modelling ecosystems: Other components


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