Organism that ingests organic carbon for nutrition
Cycle betweenautotrophs and heterotrophs. Autotrophs use light,carbon dioxide (CO2), andwater to formoxygen and complex organic compounds, mainly through the process ofphotosynthesis (green arrow). Both types of organisms use such compounds viacellular respiration to generateATP and again form CO2 and water (two red arrows).
Aheterotroph (/ˈhɛtərəˌtroʊf,-ˌtrɒf/;[1][2] fromAncient Greek ἕτερος (héteros), meaning "other", and τροφή (trophḗ), meaning "nourishment") is anorganism that cannot produce its own food, instead taking nutrition from other sources oforganic carbon, mainly matter from other organisms. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers.[3][4] Living organisms that are heterotrophic include mostanimals,[5][6] allfungi, somebacteria andprotists,[7] and manyparasitic plants. The term heterotroph arose inmicrobiology in 1946 as part of a classification ofmicroorganisms based on their type ofnutrition.[8] The term is now used in many fields, such asecology, in describing thefood chain. Heterotrophs occupy the second and third trophic levels of the food chain while autotrophs occupy the first trophic level.[9]
Heterotrophs represent one of the two mechanisms of nutrition (trophic levels), the other beingautotrophs (auto = self,troph = nutrition). Autotrophs use energy fromsunlight (photoautotrophs) or oxidation of inorganic compounds (lithoautotrophs) to convert inorganiccarbon dioxide to organic carbon compounds and energy to sustain their life. Comparing the two in basic terms, heterotrophs (such as animals) eat either autotrophs (such as plants) or other heterotrophs, or both.
Organoheterotrophs exploit reduced carbon compounds (organics) as electron sources, such ascarbohydrates,fats, andproteins from plants and animals.
Lithoheterotrophs, on the other hand, use inorganic compounds such asammonium,nitrite, orsulfur, to obtain electrons.
Another way of classifying different heterotrophs is by assigning them aschemotrophs orphototrophs. Phototrophs utilize light to obtain energy and carry out metabolic processes, whereas chemotrophs use the energy obtained by the oxidation of chemicals from their environment.[12]
Photoorganoheterotrophs, such asRhodospirillaceae and purple non-sulfur bacteria synthesize organic compounds using sunlight coupled with oxidation of organic substances. They use organic compounds to build structures. They do not fix carbon dioxide and apparently do not have theCalvin cycle.[13]
Chemolithoheterotrophs likeOceanithermus profundus[14] obtain energy from the oxidation of inorganic compounds, includinghydrogen sulfide, elementalsulfur,thiosulfate, and molecularhydrogen.
Mixotrophs (or facultative chemolithotroph) can use either carbon dioxide or organic carbon as the carbon source, meaning that mixotrophs have the ability to use both heterotrophic and autotrophic methods.[15][16] Although mixotrophs have the ability to grow under both heterotrophic and autotrophic conditions,C. vulgaris have higher biomass and lipid productivity when growing under heterotrophic compared to autotrophic conditions.[17]
Heterotrophs, by consuming reduced carbon compounds, are able to use all the energy that they obtain from food for growth and reproduction, unlike autotrophs, which must use some of their energy for carbon fixation.[13] Both heterotrophs and autotrophs alike are usually dependent on the metabolic activities of other organisms for nutrients other than carbon, including nitrogen, phosphorus, and sulfur, and can die from lack of food that supplies these nutrients.[18] This applies not only to animals and fungi but also to bacteria.[13]
The chemicalorigin of life hypothesis suggests that life originated in aprebiotic soup with heterotrophs.[19] The summary of this theory is as follows: early Earth had a highlyreducing atmosphere and energy sources such as electrical energy in the form of lightning, which resulted in reactions that formed simpleorganic compounds, which further reacted to form more complex compounds and eventually resulted in life.[20][21] Alternative theories of an autotrophic origin of life contradict this theory.[22]
The theory of a chemical origin of life beginning with heterotrophic life was first proposed in 1924 byAlexander Ivanovich Oparin, and eventually published "The Origin of Life."[23] It was independently proposed for the first time in English in 1929 byJohn Burdon Sanderson Haldane.[24] While these authors agreed on the gasses present and the progression of events to a point, Oparin championed a progressive complexity of organic matter prior to the formation of cells, while Haldane had more considerations about the concept of genes as units of heredity and the possibility of light playing a role in chemical synthesis (autotrophy).[25]
Evidence grew to support this theory in 1953, whenStanley Miller conducted anexperiment in which he added gasses that were thought to be present onearly Earth – water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2) – to a flask and stimulated them with electricity that resembled lightning present on early Earth.[26] The experiment resulted in the discovery that early Earth conditions were supportive of the production of amino acids, with recent re-analyses of the data recognizing that over 40 different amino acids were produced, including several not currently used by life.[19] This experiment heralded the beginning of the field of synthetic prebiotic chemistry, and is now known as theMiller–Urey experiment.[27]
On early Earth, oceans and shallow waters were rich with organic molecules that could have been used by primitive heterotrophs.[28] This method of obtaining energy was energetically favorable until organic carbon became more scarce than inorganic carbon, providing a potential evolutionary pressure to become autotrophic.[28][29] Following the evolution of autotrophs, heterotrophs were able to utilize them as a food source instead of relying on the limited nutrients found in their environment.[30] Eventually, autotrophic and heterotrophic cells were engulfed by these early heterotrophs and formed asymbiotic relationship.[30] Theendosymbiosis of autotrophic cells is suggested to have evolved into thechloroplasts while the endosymbiosis of smaller heterotrophs developed into themitochondria, allowing the differentiation of tissues and development into multicellularity. This advancement allowed the further diversification of heterotrophs.[30] Today, many heterotrophs and autotrophs also utilizemutualistic relationships that provide needed resources to both organisms.[31] One example of this is the mutualism between corals and algae, where the former provides protection and necessary compounds for photosynthesis while the latter provides oxygen.[32]
However this hypothesis is controversial as CO2 was the main carbon source at the early Earth, suggesting that early cellular life were autotrophs that relied upon inorganic substrates as an energy source and lived at alkaline hydrothermal vents or acidic geothermal ponds.[33] Simple biomolecules transported from space was considered to have been either too reduced to have been fermented or too heterogeneous to support microbial growth.[34] Heterotrophic microbes likely originated at low H2 partial pressures. Bases, amino acids, and ribose are considered to be the first fermentation substrates.[35]
Heterotrophs are currently found in each domain of life:Bacteria,Archaea, andEukarya.[36] Domain Bacteria includes a variety of metabolic activity including photoheterotrophs, chemoheterotrophs, organotrophs, and heterolithotrophs.[36] Within Domain Eukarya, kingdomsFungi andAnimalia are entirely heterotrophic, though most fungi absorb nutrients through their environment.[37][38] Most organisms within KingdomProtista are heterotrophic while KingdomPlantae is almost entirely autotrophic, except formyco-heterotrophic plants.[37] Lastly, Domain Archaea varies immensely in metabolic functions and contains many methods of heterotrophy.[36]
Many heterotrophs arechemoorganoheterotrophs that use organic carbon (e.g. glucose) as their carbon source, and organic chemicals (e.g. carbohydrates, lipids, proteins) as their electron sources.[39] Heterotrophs function asconsumers in food chain: they obtain these nutrients fromsaprotrophic,parasitic, orholozoic nutrients.[40] They break down complex organic compounds (e.g., carbohydrates, fats, and proteins) produced by autotrophs into simpler compounds (e.g., carbohydrates intoglucose, fats intofatty acids andglycerol, and proteins intoamino acids). They release the chemical energy of nutrient molecules by oxidizing carbon and hydrogen atoms from carbohydrates, lipids, and proteins to carbon dioxide and water, respectively.
They can catabolize organic compounds by respiration, fermentation, or both.Fermenting heterotrophs are either facultative or obligateanaerobes that carry out fermentation in low oxygen environments, in which the production of ATP is commonly coupled withsubstrate-level phosphorylation and the production of end products (e.g. alcohol, CO2, sulfide).[41] These products can then serve as the substrates for other bacteria in theanaerobic digestion, and be converted into CO2 and CH4, which is an important step for thecarbon cycle for removing organic fermentation products from anaerobic environments.[41] Heterotrophs can undergorespiration, in which ATP production is coupled withoxidative phosphorylation.[41][42] This leads to the release of oxidized carbon wastes such as CO2 and reduced wastes like H2O, H2S, or N2O into the atmosphere. Heterotrophic microbes' respiration and fermentation account for a large portion of the release of CO2 into the atmosphere, making it available for autotrophs as a source of nutrient and plants as a cellulose synthesis substrate.[43][42]
Respiration in heterotrophs is often accompanied bymineralization, the process of converting organic compounds to inorganic forms.[43] When the organic nutrient source taken in by the heterotroph contains essential elements such as N, S, P in addition to C, H, and O, they are often removed first to proceed with the oxidation of organic nutrient and production of ATP via respiration.[43] S and N in organic carbon source are transformed into H2S and NH4+ through desulfurylation anddeamination, respectively.[43][42] Heterotrophs also allow fordephosphorylation as part ofdecomposition.[42] The conversion of N and S from organic form to inorganic form is a critical part of thenitrogen andsulfur cycle. H2S formed from desulfurylation is further oxidized by lithotrophs and phototrophs while NH4+ formed from deamination is further oxidized by lithotrophs to the forms available to plants.[43][42] Heterotrophs' ability to mineralize essential elements is critical to plant survival.[42]
Mostopisthokonts andprokaryotes are heterotrophic; in particular, all animals and fungi are heterotrophs.[7] Some animals, such ascorals, formsymbiotic relationships with autotrophs and obtain organic carbon in this way. Furthermore, someparasitic plants have also turned fully or partially heterotrophic, whilecarnivorous plants consume animals to augment their nitrogen supply while remaining autotrophic.
Animals are classified as heterotrophs by ingestion, fungi are classified as heterotrophs by absorption.
Heterotrophs, organisms that obtain energy and carbon by consuming organic matter, are vital parts of Earth's biogeochemical cycles particularly in the carbon, nitrogen, and sulfur cycles. Their metabolic activities impact the processing and cycling of elements through ecosystems and the biosphere.
Heterotrophs are key players in the carbon cycle, acting as both consumers and decomposers. They release carbon dioxide (CO2) into the atmosphere through respiration, contributing to a large portion of carbon dioxide emissions.[44] This process makes carbon available for autotrophs, who can fix carbon through photosynthesis or chemosynthesis. This circulation supports the continuous cycling of carbon between organic and inorganic forms.[45]
Heterotrophic organisms contribute to key processes in the nitrogen cycle like ammonification, the conversion of organic nitrogen to ammonia, and denitrification, the reduction of nitrate and the release of nitrogen gas to the atmosphere.[46] These processes can be known as secondary metabolism in heterotrophs.[47] Heterotrophic microorganisms are essential in the mineralization of organic compounds containing nitrogen.[48][49] Through deamination, they convert organic nitrogen to ammonium (NH4+), which can be further oxidized by lithotrophs into forms available to plants. Similarly, desulfurylation by heterotrophs transforms organic sulfur into hydrogen sulfide (H2S), which is then oxidized by lithotrophs and phototrophs, contributing to the sulfur cycle.
The ability of heterotrophs to break down complex organic compounds is fundamental to nutrient cycling in ecosystems.[50] By decomposing dead organic matter, they release essential elements like phosphorus through dephosphorylation, making these nutrients available for other organisms.[51] This process is critical for maintaining soil fertility and supporting plant growth. Heterotrops connect the flow of energy and organic matter across ecosystems. Their biological processes link with atmospheric, chemical and geological systems.[52]
Heterotrophs form intricate relationships with autotrophs in ecosystems. While they depend on autotrophs for energy-rich organic compounds, heterotrophs support autotrophic growth by releasing minerals and carbon dioxide (CO2). This interdependence is exemplified in symbiotic relationships, such as those between corals and algae, where nutrient exchange benefits both partners. Their metabolic processes depend on each other and traces of organic compounds.[53]
The biogeochemical activities of heterotrophs are thus integral to ecosystem functioning, influencing the availability of nutrients, the composition of the atmosphere, and the productivity of both terrestrial and aquatic environments.
Heterotrophs, organisms that obtain energy and carbon by consuming organic matter, are vital parts of Earth's biogeochemical cycles particularly in the carbon, nitrogen, and sulfur cycles. Their metabolic activities impact the processing and cycling of elements through ecosystems and the biosphere.
Heterotrophs are key players in the carbon cycle, acting as both consumers and decomposers. They release carbon dioxide (CO2) into the atmosphere through respiration, contributing to a large portion of carbon dioxide emissions. This process makes carbon available for autotrophs, who can fix carbon through photosynthesis or chemosynthesis. This circulation supports the continuous cycling of carbon between organic and inorganic forms.[54]
Heterotrophic organisms contribute to key processes in the nitrogen cycle like ammonification, the conversion of organic nitrogen to ammonia, and denitrification, the reduction of nitrate and the release of nitrogen gas to the atmosphere.[55] Heterotrophic microorganisms are essential in the mineralization of organic compounds containing nitrogen.[56] Through deamination, they convert organic nitrogen to ammonium (NH4+), which can be further oxidized by lithotrophs into forms available to plants. Similarly, desulfurylation by heterotrophs transforms organic sulfur into hydrogen sulfide (H2S), which is then oxidized by lithotrophs and phototrophs, contributing to the sulfur cycle.
The ability of heterotrophs to break down complex organic compounds is fundamental to nutrient cycling in ecosystems. By decomposing dead organic matter, they release essential elements like phosphorus through dephosphorylation, making these nutrients available for other organisms. This process is critical for maintaining soil fertility and supporting plant growth. Heterotrops connect the flow of energy and organic matter across ecosystems. Their biological processes link with atmospheric, chemical and geological systems.[57]
Heterotrophs form intricate relationships with autotrophs in ecosystems. While they depend on autotrophs for energy-rich organic compounds, heterotrophs support autotrophic growth by releasing minerals and carbon dioxide (CO2). This interdependence is exemplified in symbiotic relationships, such as those between corals and algae, where nutrient exchange benefits both partners.[58]
The biogeochemical activities of heterotrophs are thus integral to ecosystem functioning, influencing the availability of nutrients, the composition of the atmosphere, and the productivity of both terrestrial and aquatic environments.
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^Jordan, Carl F (2022), "A Thermodynamic View of Evolution",Evolution from a Thermodynamic Perspective, Cham: Springer International Publishing, pp. 157–199,doi:10.1007/978-3-030-85186-6_12,ISBN978-3-030-85185-9{{citation}}: CS1 maint: work parameter with ISBN (link)
^abTaylor, D. L.; Bruns, T. D.; Leake, J. R.; Read, D. J. (2002),Mycorrhizal Specificity and Function in Myco-heterotrophic Plants, Ecological Studies, vol. 157, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 375–413,doi:10.1007/978-3-540-38364-2_15,ISBN978-3-540-00204-8
^Werner, Dietrich (1977).The Biology of Diatoms. University of California Press. pp. 170–181.
^Schlesinger, William H.; Bernhardt, Emily S. (2020).Biogeochemistry: an analysis of global change (4th ed.). Waltham, MA: Academic Press, an imprint of Elsevier.ISBN978-0-12-814609-5.
^Kerr, P. C., Paris, D. F., & Brockway, D. L. (1970).The interrelation of carbon and phosphorus in regulating heterotrophic and autotrophic populations in aquatic ecosystems (Report No. FWQA-16050-FGS-07/70). U.S. Federal Water Quality Administration.
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