chemosynthesis


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chemosynthesis,

process in which carbohydrates are manufactured from carbon dioxide and water using chemical nutrients as the energy source, rather than the sunlight used for energy in photosynthesisphotosynthesis
, process in which green plants, algae, and cyanobacteria utilize the energy of sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. Some of the plants that lack chlorophyll, e.g.
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. Much life on earth is fueled directly or indirectly by sunlight. There are, however, certain groups of bacteria, referred to as chemosynthetic autotrophs, that are fueled not by the sun but by the oxidation of simple inorganic chemicals, such as sulfates or ammonia. Chemosynthetic autotrophs are a necessary part of the nitrogen cyclenitrogen cycle,
the continuous flow of nitrogen through the biosphere by the processes of nitrogen fixation, ammonification (decay), nitrification, and denitrification. Nitrogen is vital to all living matter, both plant and animal; it is an essential constituent of amino acids,
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. Some groups of these bacteria are well suited to conditions that would have existed on the earth billions of years ago, leading some to postulate that these are living representatives of the earliest life on earth. This view has been supported by the discovery of ecosystems that thrive in the hot (350°C;/660°F;) water found around hydrothermal vents on the ocean floor. In these ecosystems, the primary producers in the food web are bacteria whose life functions are fueled by inorganic chemicals that seep up from the earth's crust. Other chemosynthetic bacteria are found deep underground, utilizing nitrogen and sulfur compounds as energy sources. See also autotrophautotroph
, in biology, an organism capable of synthesizing its own organic substances from inorganic compounds. Autotrophs produce their own sugars, lipids, and amino acids using carbon dioxide as a source of carbon, and ammonia or nitrates as a source of nitrogen.
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.

Chemosynthesis

 

a type of nutrition characteristic of certain bacteria whose only carbon source is CO2 obtained from the energy of oxidation of inorganic compounds.

The discovery of chemosynthesis by S. N. Vinogradskii in 1887 significantly altered prevailing views on the main types of metabolism in living organisms. Unlike photosynthesis, chemosynthesis does not involve the use of light energy but energy derived from oxidation-reductions that must be adequate for the synthesis of adenosine triphosphate (ATP) and that must exceed 10 kcal/mole. Chemosynthetic bacteria are not strictly a taxonomic group; they are classified according to the inorganic substrate they oxidize. They include microorganisms that oxidize hydrogen, carbon monoxide, reduced sulfur compounds, iron, ammonia, nitrites, and antimony.

Hydrogen bacteria are the most numerous and varied group of chemosynthetic organisms. They perform the reaction 6H2 + 2O2 + CO2 = (CH2O) + 5H2O, in which (CH2O) is the conventional designation of the organic substances formed. Compared with other autotrophic microorganisms, hydrogen bacteria have a high growth rate and may produce a large biomass; they are also able to grow on mediums containing organic matter, that is, they are mixotrophic or facultatively chemoautotrophic.

Carboxydation bacteria are similar to hydrogen bacteria, but they oxidize CO by the reaction 25CO + 12O2 + H2O + 24CO2+ (CH2O). Sulfur bacteria oxidize hydrogen sulfide, thiosulfate, and molecular sulfur to sulfuric acid. Some, for example, Thiobacillus ferrooxidans, oxidize sulfide minerals and ferrous oxide. The capacity of various aquatic sulfur bacteria for chemosynthesis has not yet been demonstrated. Nitrifying bacteria oxidize ammonia to nitrite (first stage of nitrification) and nitrite to nitrate (second stage). Chemosynthesis occurs under anaerobic conditions in some denitrifying bacteria, which oxidize hydrogen or sulfur but often require organic matter for biosynthesis. Chemosynthesis has been described in some strictly anaerobic meth-anogenic bacteria according to the reaction 4H2 + CO2 = CH4 + 2H2O.

The biosynthesis of organic compounds in chemosynthesis is achieved by autotrophic assimilation of CO2 (Calvin carbon reduction cycle) just as in photosynthesis. Energy is obtained in the form of ATP from electron transfer via the chain of respiratory enzymes incorporated into the bacterial cell membrane. Some oxidized substances give off electrons to the chain at the cytochrome c level, thereby creating additional energy to synthesize the reducing agent. Owing to the fairly large consumption of energy, chemosynthetic bacteria—with the exception of hydrogen bacteria—produce a small biomass but oxidize a substantial amount of inorganic matter. Since chemosynthetic bacteria control the oxidative parts of the cycle of major elements in the biosphere, they are vitally important in biogeochemistry. Hydrogen bacteria can be used to obtain protein and to free the atmosphere from CO2 in closed ecological systems. Chemosynthetic bacteria are highly varied morphologically. Although most of them are pseudomonades, they are also found among budding and filamentous bacteria, spirilla, leptospira, and corynebacteria.

REFERENCES

Kuznetsov, S. I. Mikroflora ozer i ee geokhimicheskaia deiatel’nost’. Leningrad, 1970.
Zavarzin, G. A. Litotrofnye mikroorganizmy. Moscow, 1972.
Karavaiko, G. I., S. I. Kuznetsov, and A. I. Golomzik. Rol’ mikroorganizmov v vyshelachivanii metallov iz rud. Moscow, 1972.

G. A. ZAVARZIN

chemosynthesis

[‚kē·mō′sin·thə·səs]
(biochemistry)
The synthesis of organic compounds from carbon dioxide by microorganisms using energy derived from chemical reactions.
References in periodicals archive ?
Chang, "Comparison of magnetite nanocrystal formed by biomineralization and chemosynthesis," Journal of Magnetism and Magnetic Materials, vol.
The Guaymas Basin in the Gulf of California is JASON IV's chemosynthesis site.
coli, which is a clinical useful peptide, and was produced by chemosynthesis previously.
The successive discoveries of populations of organisms previously only found in hydrothermal vents, such as vestimentiferans and bivalves, in other anoxic, methane- and hydrogen sulfide-rich environments, and of populations of metabolically versatile archeobacteria, some free-living and others in symbiosis with different animals, leads one to conclude that hydrogen sulfide-based chemosynthesis is a much more widespread basis for primary production than was thought just a few years ago, when hydrothermal oases were first discovered.
I close the redox section by showing a slide of the life in the deep sea vents and I point out that vent life is based on chemosynthesis for its energy, not photosynthesis [39].
Van Dover, Blankenship, and others agree that deep-sea photosynthetic organisms-if they exist-probably subsist mostly on chemosynthesis and use the light only for supplemental nourishment.
His findings lend credence to the theory that life on Earth started through chemosynthesis, the reaction of chemicals without sunlight, rather than photosynthesis, the reaction of chemicals with sunlight.
This study investigates the magnetic fluids, with a view to form magnetic nanoparticles of different shapes and sizes under the control of chemosynthesis [14-18] and then to mix them with PDMS to make magnetic fluid with various solid loadings.
To scientists' utter astonishment, the vents were surrounded by previously unknown organisms sustained not by photosynthesis but chemosynthesis. The discovery completely rearranged our conceptions of where and how life can exist on this planet and elsewhere in the universe.
Chemosynthesis: an alternative hypothesis for Carboniferous biotas in bryozoan/ microbial mounds, Newfoundland, Canada.
To survive, they may have absorbed nutrients from seawater or harbored symbiotic microbes that provided nourishment through photosynthesis or chemosynthesis.
KEY WORDS: shrimp, Mid-Atlantic Ridge, hydrothermal vents, deep-sea, symbiosis, biomineralization, chemosynthesis, microorganisms, extreme environments