Editing Heterotroph

{{Short description|Organism that ingests organic carbon for nutrition}}
[[File:Auto-and heterotrophs.png|thumb|300px|Cycle between [[autotroph]]s and heterotrophs. Autotrophs use light, [[carbon dioxide]] (CO<sub>2</sub>), and [[water]] to form [[oxygen]] and complex organic compounds, mainly through the process of [[photosynthesis]] (green arrow). Both types of organisms use such compounds via [[cellular respiration]] to generate [[adenosine triphosphate|ATP]] and again form CO<sub>2</sub> and water (two red arrows).]]

A '''heterotroph''' ({{IPAc-en|ˈ|h|ɛ|t|ər|ə|ˌ|t|r|oʊ|f|,_|-|ˌ|t|r|ɒ|f}};<ref>{{cite Dictionary.com|heterotroph}}</ref><ref>{{cite Merriam-Webster|heterotroph}}</ref> {{etymology|grc|''{{wikt-lang|grc|ἕτερος}}'' ({{grc-transl|ἕτερος}})|other||''{{wikt-lang|grc|τροφή}}'' ({{grc-transl|τροφή}})|nutrition}}) is an [[organism]] that cannot produce its own food,  instead taking nutrition from other sources of [[organic carbon]], mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but not producers.<ref>{{cite web |title=Heterotroph Definition |publisher=Biology Dictionary |url=https://biologydictionary.net/heterotroph |date=April 28, 2017 |access-date=2023-12-02}}</ref><ref name="essential microbiology">{{cite book |last= Hogg|first=Stuart |title=Essential Microbiology |year=2013 |edition=2nd |publisher=[[Wiley-Blackwell]] |page=86 |isbn=978-1-119-97890-9}}</ref> Living organisms that are heterotrophic include all [[animal]]s and [[fungi]], some [[bacteria]] and [[protist]]s,<ref name="cell">{{cite web |url=http://highered.mcgraw-hill.com/sites/dl/free/0072965819/415836/rav65819_ch07.pdf |title=How Cells Harvest Energy |publisher=[[McGraw Hill Education|McGraw-Hill Higher Education]] |access-date=2010-10-10 |archive-url=https://web.archive.org/web/20120731144141/http://highered.mcgraw-hill.com/sites/dl/free/0072965819/415836/rav65819_ch07.pdf |archive-date=2012-07-31 |url-status=dead}}</ref> and many [[parasitic plant]]s. The term heterotroph arose in [[microbiology]] in 1946 as part of a classification of [[microorganisms]] based on their type of [[Primary nutritional groups|nutrition]].<ref>{{cite conference |author1=Lwoff, A. |author2=C.B. van Niel |author3=P.J. Ryan |author4=E.L. Tatum |year=1946 |title=Nomenclature of nutritional types of microorganisms |conference=Cold Spring Harbor Symposia on Quantitative Biology |edition=5th |volume=XI |publisher=The Biological Laboratory |place=Cold Spring Harbor, N.Y. |pages=302–303 |url=http://symposium.cshlp.org/content/11/local/back-matter.pdf |archive-url=https://web.archive.org/web/20171107221024/http://symposium.cshlp.org/content/11/local/back-matter.pdf |archive-date=2017-11-07 |url-status=live}}</ref> The term is now used in many fields, such as [[ecology]], in describing the [[food chain]]. Heterotrophs occupy the second and third trophic levels of the food chain while autotrophs occupy the first trophic level.<ref>{{Cite web |title=Heterotrophs |url=https://education.nationalgeographic.org/resource/heterotrophs/ |access-date=2025-02-10 |website=education.nationalgeographic.org |language=en}}</ref>

Heterotrophs may be subdivided according to their energy source. If the heterotroph uses chemical energy, it is a [[chemotroph|chemoheterotroph]] (e.g., humans and mushrooms). If it uses light for energy, then it is a [[photoheterotroph]] (e.g., [[green non-sulfur bacteria]]).

Heterotrophs represent one of the two mechanisms of nutrition ([[trophic level]]s), the other being [[autotroph]]s (''auto'' = self, ''troph'' = nutrition). Autotrophs use energy from [[sunlight]] ([[photoautotroph]]s) or oxidation of inorganic compounds ([[lithoautotroph]]s) to convert inorganic [[carbon 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.
 
[[Detritivore]]s are heterotrophs which obtain [[nutrient]]s by consuming [[detritus]] (decomposing plant and animal parts as well as [[feces]]).<ref>{{cite book |author=Wetzel, R.G. |year=2001 |title=Limnology: Lake and river ecosystems |publisher=Academic Press |edition=3rd |page=700}}</ref> [[Saprotroph]]s (also called lysotrophs) are [[chemoheterotroph]]s that use [[extracellular digestion]] in processing decayed organic matter. The process is most often facilitated through the [[active transport]] of such materials through [[endocytosis]] within the internal mycelium and its constituent [[hypha]]e.<ref name="advanced_biology_principles_1">"The purpose of saprotrophs and their internal nutrition, as well as the main two types of fungi that are most often referred to, as well as describes, visually, the process of saprotrophic nutrition through a diagram of hyphae, referring to the Rhizobium on damp, stale whole-meal bread or rotting fruit." ''Advanced Biology Principles, p&nbsp;296.{{full citation needed|date=December 2019}}</ref>

==Types==
Heterotrophs can be [[organotroph]]s or [[lithotroph]]s. Organotrophs exploit reduced carbon compounds as electron sources, like [[carbohydrates]], [[fat]]s, and [[proteins]] from plants and animals. On the other hand, lithoheterotrophs use inorganic compounds, such as [[ammonium]], [[nitrite]], or [[sulfur]], to obtain electrons. Another way of classifying different heterotrophs is by assigning them as [[chemotroph]]s or [[phototroph]]s. 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.<ref>{{cite book |last1=Mills |first1=A.L. |title=The Environmental Geochemistry of Mineral Deposits: Part A: Processes, Techniques, and Health Issues Part B: Case Studies and Research Topics |year=1997 |publisher=Society of Economic Geologists |isbn=978-1-62949-013-7 |pages=125–132 |url=http://lmecol.evsc.virginia.edu/pubs/C13-Mills_Bull%20Econ%20Geol%20.PDF |access-date=9 October 2017 |archive-date=6 April 2019 |archive-url=https://web.archive.org/web/20190406194730/https://lmecol.evsc.virginia.edu/pubs/C13-Mills_Bull%20Econ%20Geol%20.PDF |url-status=dead }}</ref>

Photoorganoheterotrophs, such as [[Rhodospirillaceae]] 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 the [[Light-independent reactions#Calvin Cycle|Calvin cycle]].<ref name="botany">{{cite book |last=Mauseth |first=James D. |title=Botany: An introduction to plant biology |year=2008 |edition=4th |publisher=Jones & Bartlett Publishers |page=[https://archive.org/details/botanyintroducti0000maus_k4i0/page/252 252] |url=https://archive.org/details/botanyintroducti0000maus_k4i0 |url-access=registration |quote=heterotroph fix carbon. |isbn=978-0-7637-5345-0}}</ref> Chemolithoheterotrophs like ''Oceanithermus profundus''<ref>{{cite journal |author1=Miroshnichenko, M.L. |author2=L'Haridon, S. |author3=Jeanthon, C. |author4=Antipov, A.N. |author5=Kostrikina, N.A. |author6=Tindall, B.J. |author7=Schumann, P. |author8=Spring, S. |author9=Stackebrandt, E. |author10=Bonch-Osmolovskaya, E.A. |display-authors=6 |date=1 May 2003 |journal=International Journal of Systematic and Evolutionary Microbiology |volume=53 |issue=3 |pages=747–752 |doi=10.1099/ijs.0.02367-0 |pmid=12807196 |title=Oceanithermus profundus gen. nov., sp. nov., a thermophilic, microaerophilic, facultatively chemolithoheterotrophic bacterium from a deep-sea hydrothermal vent|doi-access=free }}</ref> obtain energy from the oxidation of inorganic compounds, including [[hydrogen sulfide]], elemental [[sulfur]], [[thiosulfate]], and molecular [[hydrogen]]. [[Mixotroph]]s (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.<ref name="biogeochemistry">{{cite book |last=Libes |first=Susan M. |title=Introduction to Marine Biogeochemistry |year=2009 |edition=2nd |publisher=Academic Press |page=192 |url=https://books.google.com/books?id=KVZJUw4nORgC&q=chemolithoheterotrophs+inorganic&pg=PA192 |isbn=978-0-12-088530-5}}</ref><ref name="prokaryotes">{{cite book |last=Dworkin |first=Martin |title=The prokaryotes: ecophysiology and biochemistry |year=2006 |edition=3rd |publisher=Springer |page=988 |url=https://books.google.com/books?id=uleTr2jKzJMC&q=chemolithoheterotroph+chemoorganoheterotroph&pg=PA988 |isbn=978-0-387-25492-0}}</ref>
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.<ref>{{cite journal |last1=Liang |first1=Yanna |title=Biomass and lipid productivities of Chlorella vulgaris under autotrophic, heterotrophic and mixotrophic growth conditions |journal=Biotechnology Letters |date=July 2009 |volume=31 |issue=7 |pages=1043–1049 |doi=10.1007/s10529-009-9975-7 |pmid=19322523|s2cid=1989922 }}</ref>

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.<ref name="botany" /> 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.<ref>{{cite book |last1=Campbell and Reece |title=Biology |url=https://archive.org/details/biologyc00camp |url-access=registration |year=2002 |publisher=Benjamin-Cummings Publishing Co. |isbn=978-0805371710 |edition=7th}}</ref> This applies not only to animals and fungi but also to bacteria.<ref name="botany" />

== Origin and diversification ==
The chemical [[Origin of Life|origin of life]] hypothesis suggests that life originated in a [[Primordial soup|prebiotic soup]] with heterotrophs.<ref name=":03">{{Cite journal |last=Bada |first=Jeffrey L. |date=2013 |title=New insights into prebiotic chemistry from Stanley Miller's spark discharge experiments |url=http://xlink.rsc.org/?DOI=c3cs35433d |journal=Chemical Society Reviews |language=en |volume=42 |issue=5 |pages=2186–2196 |doi=10.1039/c3cs35433d |pmid=23340907 |bibcode=2013CSRev..42.2186B |issn=0306-0012}}</ref> The summary of this theory is as follows: early Earth had a highly [[reducing atmosphere]] and energy sources such as electrical energy in the form of lightning, which resulted in reactions that formed simple [[organic compound]]s, which further reacted to form more complex compounds and eventually resulted in life.<ref>{{Cite journal |last=Bracher |first=Paul J. |date=2015 |title=Primordial soup that cooks itself |url=http://www.nature.com/articles/nchem.2219 |journal=Nature Chemistry |language=en |volume=7 |issue=4 |pages=273–274 |doi=10.1038/nchem.2219 |pmid=25803461 |bibcode=2015NatCh...7..273B |issn=1755-4330}}</ref><ref>{{Citation |last=Lazcano |first=Antonio |title=Primordial Soup |date=2015 |url=http://link.springer.com/10.1007/978-3-662-44185-5_1275 |encyclopedia=Encyclopedia of Astrobiology |pages=2010–2014 |editor-last=Gargaud |editor-first=Muriel |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-662-44185-5_1275 |bibcode=2015enas.book.2010L |isbn=978-3-662-44184-8 |access-date=2022-04-23 |editor2-last=Irvine |editor2-first=William M. |editor3-last=Amils |editor3-first=Ricardo |editor4-last=Cleaves |editor4-first=Henderson James}}</ref> Alternative theories of an autotrophic origin of life contradict this theory.<ref>{{Cite journal |last1=Schönheit |first1=Peter |last2=Buckel |first2=Wolfgang |last3=Martin |first3=William F. |date=2016 |title=On the Origin of Heterotrophy |url=https://linkinghub.elsevier.com/retrieve/pii/S0966842X15002292 |journal=Trends in Microbiology |language=en |volume=24 |issue=1 |pages=12–25 |doi=10.1016/j.tim.2015.10.003|pmid=26578093 }}</ref>

The theory of a chemical origin of life beginning with heterotrophic life was first proposed in 1924 by [[Alexander Oparin|Alexander Ivanovich Oparin]], and eventually published "The Origin of Life."<ref>{{Cite journal |last1=Sanger |first1=F. |last2=Thompson |first2=E. O. P. |date=1953-02-01 |title=The amino-acid sequence in the glycyl chain of insulin. 1. The identification of lower peptides from partial hydrolysates |url=http://dx.doi.org/10.1042/bj0530353 |journal=Biochemical Journal |volume=53 |issue=3 |pages=353–366 |doi=10.1042/bj0530353 |pmid=13032078 |pmc=1198157 |issn=0306-3283}}</ref> It was independently proposed for the first time in English in 1929 by [[J. B. S. Haldane|John Burdon Sanderson Haldane]].<ref>Haldane, J.B.S. (1929) The Origin of Life. The Rationalist Annual, 3, 3–10.</ref> 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 ([[autotroph]]y).<ref>{{Cite journal |last=Tirard |first=Stéphane |date=2017 |title=J. B. S. Haldane and the origin of life |url=http://link.springer.com/10.1007/s12041-017-0831-6 |journal=Journal of Genetics |language=en |volume=96 |issue=5 |pages=735–739 |doi=10.1007/s12041-017-0831-6 |pmid=29237880 |s2cid=28775520 |issn=0022-1333}}</ref>  

Evidence grew to support this theory in 1953, when [[Stanley Miller]] conducted an [[Miller–Urey experiment|experiment]] in which he added gasses that were thought to be present on [[early Earth]] – water (H<sub>2</sub>O), methane (CH<sub>4</sub>), ammonia (NH<sub>3</sub>), and hydrogen (H<sub>2</sub>) – to a flask and stimulated them with electricity that resembled lightning present on early Earth.<ref>{{Cite journal |last=Miller |first=Stanley L. |date=1953-05-15 |title=A Production of Amino Acids Under Possible Primitive Earth Conditions |url=https://www.science.org/doi/10.1126/science.117.3046.528 |journal=Science |language=en |volume=117 |issue=3046 |pages=528–529 |doi=10.1126/science.117.3046.528 |pmid=13056598 |bibcode=1953Sci...117..528M |issn=0036-8075}}</ref> 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.<ref name=":03" /> This experiment heralded the beginning of the field of synthetic prebiotic chemistry, and is now known as the [[Miller–Urey experiment]].<ref>{{Cite journal |last1=Lazcano |first1=Antonio |last2=Bada |first2=Jeffrey L. |title=The 1953 Stanley L. Miller experiment: Fifty years of prebiotic organic chemistry |date=2003 |url=http://link.springer.com/10.1023/A:1024807125069 |journal=Origins of Life and Evolution of the Biosphere |volume=33 |issue=3 |pages=235–242 |doi=10.1023/A:1024807125069|pmid=14515862 |bibcode=2003OLEB...33..235L |s2cid=19515024 }}</ref>

On early Earth, oceans and shallow waters were rich with organic molecules that could have been used by primitive heterotrophs.<ref name=":12">{{Cite journal |last1=Preiner |first1=Martina |last2=Asche |first2=Silke |last3=Becker |first3=Sidney |last4=Betts |first4=Holly C. |last5=Boniface |first5=Adrien |last6=Camprubi |first6=Eloi |last7=Chandru |first7=Kuhan |last8=Erastova |first8=Valentina |last9=Garg |first9=Sriram G. |last10=Khawaja |first10=Nozair |last11=Kostyrka |first11=Gladys |date=2020-02-26 |title=The Future of Origin of Life Research: Bridging Decades-Old Divisions |journal=Life |volume=10 |issue=3 |pages=20 |doi=10.3390/life10030020 |pmid=32110893 |pmc=7151616 |issn=2075-1729|doi-access=free |bibcode=2020Life...10...20P }}</ref> 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.<ref name=":12" /><ref>{{Citation |last=Jordan |first=Carl F |title=A Thermodynamic View of Evolution |url=http://dx.doi.org/10.1007/978-3-030-85186-6_12 |work=Evolution from a Thermodynamic Perspective |year=2022 |pages=157–199 |place=Cham |publisher=Springer International Publishing |doi=10.1007/978-3-030-85186-6_12 |isbn=978-3-030-85185-9 |access-date=2022-04-23}}</ref> 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.<ref name=":22">{{Cite journal |last1=Zachar |first1=István |last2=Boza |first2=Gergely |date=2020-02-01 |title=Endosymbiosis before eukaryotes: mitochondrial establishment in protoeukaryotes |url=http://dx.doi.org/10.1007/s00018-020-03462-6 |journal=Cellular and Molecular Life Sciences |volume=77 |issue=18 |pages=3503–3523 |doi=10.1007/s00018-020-03462-6 |pmid=32008087 |pmc=7452879 |issn=1420-682X}}</ref> Eventually, autotrophic and heterotrophic cells were engulfed by these early heterotrophs and formed a [[Symbiosis|symbiotic]] relationship.<ref name=":22" /> The [[Endosymbiont|endosymbiosis]] of autotrophic cells is suggested to have evolved into the [[chloroplast]]s while the endosymbiosis of smaller heterotrophs developed into the [[Mitochondrion|mitochondria]], allowing the differentiation of tissues and development into multicellularity. This advancement allowed the further diversification of heterotrophs.<ref name=":22" /> Today, many heterotrophs and autotrophs also utilize [[Mutualism (biology)|mutualistic]] relationships that provide needed resources to both organisms.<ref>{{Cite journal |last1=Okie |first1=Jordan G. |last2=Smith |first2=Val H. |last3=Martin-Cereceda |first3=Mercedes |date=2016-05-25 |title=Major evolutionary transitions of life, metabolic scaling and the number and size of mitochondria and chloroplasts |url=http://dx.doi.org/10.1098/rspb.2016.0611 |journal=Proceedings of the Royal Society B: Biological Sciences |volume=283 |issue=1831 |pages=20160611 |doi=10.1098/rspb.2016.0611 |pmid=27194700 |pmc=4892803 |issn=0962-8452}}</ref> 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.<ref>{{Cite journal |last1=Knowlton |first1=Nancy |last2=Rohwer |first2=Forest |date=2003 |title=Multispecies Microbial Mutualisms on Coral Reefs: The Host as a Habitat |url=http://dx.doi.org/10.1086/378684 |journal=The American Naturalist |volume=162 |issue=S4 |pages=S51–S62 |doi=10.1086/378684 |pmid=14583857 |bibcode=2003ANat..162S..51K |s2cid=24127308 |issn=0003-0147}}</ref>

However this hypothesis is controversial as CO<sub>2</sub> 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.<ref>{{Cite journal |last1=Muchowska |first1=K. B. |last2=Varma |first2=S. J. |last3=Chevallot-Beroux |first3=E. |last4=Lethuillier-Karl |first4=L. |last5=Li |first5=G. |last6=Moran |first6=J. |date=October 2, 2017 |title=Metals promote sequences of the reverse Krebs cycle. |journal=Nature Ecology & Evolution |volume=1 |issue=11 |pages=1716–1721 |doi=10.1038/s41559-017-0311-7 |issn=2397-334X |pmid=28970480|pmc=5659384 |bibcode=2017NatEE...1.1716M }}</ref> Simple biomolecules transported from space was considered to have been either too reduced to have been fermented or too heterogeneous to support microbial growth.<ref>{{Cite journal |last1=Weiss |first1=Madeline C. |last2=Preiner |first2=Martina |last3=Xavier |first3=Joana C. |last4=Zimorski |first4=Verena |last5=Martin |first5=William F. |date=2018-08-16 |title=The last universal common ancestor between ancient Earth chemistry and the onset of genetics |journal=PLOS Genetics |language=en |volume=14 |issue=8 |pages=e1007518 |doi=10.1371/journal.pgen.1007518 |pmid=30114187 |pmc=6095482 |s2cid=52019935 |issn=1553-7404 |doi-access=free }}</ref> Heterotrophic microbes likely originated at low H<sub>2</sub> partial pressures. Bases, amino acids, and ribose are considered to be the first fermentation substrates.<ref>{{Cite journal |last1=Schönheit |first1=Peter |last2=Buckel |first2=Wolfgang |last3=Martin |first3=William F. |date=2016-01-01 |title=On the Origin of Heterotrophy |url=https://www.sciencedirect.com/science/article/pii/S0966842X15002292 |journal=Trends in Microbiology |language=en |volume=24 |issue=1 |pages=12–25 |doi=10.1016/j.tim.2015.10.003 |pmid=26578093 |issn=0966-842X}}</ref>

Heterotrophs are currently found in each domain of life: [[Bacteria]], [[Archaea]], and [[Eukarya]].<ref name=":3">{{Cite book |last1=Kim |first1=Byung Hong |url=http://dx.doi.org/10.1017/9781316761625 |title=Prokaryotic Metabolism and Physiology |last2=Gadd |first2=Geoffrey Michael |date=2019-05-04 |publisher=Cambridge University Press |doi=10.1017/9781316761625 |isbn=978-1-316-76162-5|s2cid=165100369 }}</ref> Domain Bacteria includes a variety of metabolic activity including photoheterotrophs, chemoheterotrophs, organotrophs, and heterolithotrophs.<ref name=":3" /> Within Domain Eukarya, kingdoms [[Fungus|Fungi]] and [[Animal]]ia are entirely heterotrophic, though most fungi absorb nutrients through their environment.<ref name=":4">{{Citation |last1=Taylor |first1=D. L. |title=Mycorrhizal Specificity and Function in Myco-heterotrophic Plants |date=2002 |url=http://dx.doi.org/10.1007/978-3-540-38364-2_15 |pages=375–413 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |isbn=978-3-540-00204-8 |access-date=2022-04-23 |last2=Bruns |first2=T. D. |last3=Leake |first3=J. R. |last4=Read |first4=D. J.|series=Ecological Studies |volume=157 |doi=10.1007/978-3-540-38364-2_15 }}</ref><ref>{{Cite journal |last=Butterfield |first=Nicholas J. |date=2011 |title=Animals and the invention of the Phanerozoic Earth system |url=http://dx.doi.org/10.1016/j.tree.2010.11.012 |journal=Trends in Ecology & Evolution |volume=26 |issue=2 |pages=81–87 |doi=10.1016/j.tree.2010.11.012 |pmid=21190752 |bibcode=2011TEcoE..26...81B |issn=0169-5347}}</ref> Most organisms within Kingdom [[Protist]]a are heterotrophic while Kingdom [[Plant]]ae is almost entirely autotrophic, except for [[Myco-heterotrophy|myco-heterotrophic]] plants.<ref name=":4" /> Lastly, Domain Archaea varies immensely in metabolic functions and contains many methods of heterotrophy.<ref name=":3" />

==Flowchart==
[[File:AutoHeteroTrophs flowchart.png|thumb|Flowchart to determine if a species is autotroph, heterotroph, or a subtype]]
*[[Autotroph]]
**[[Chemoautotroph]]
**[[Photoautotroph]]
*'''Heterotroph'''
**[[Chemoheterotroph]]
**[[Photoheterotroph]]

==Ecology==
{{Main|Consumer (food chain)}}

Many heterotrophs are [[Organotroph|chemoorganoheterotrophs]] that use organic carbon (e.g. glucose) as their carbon source, and organic chemicals (e.g. carbohydrates, lipids, proteins) as their electron sources.<ref>{{cite web |url=http://lmecol.evsc.virginia.edu/pubs/C13-Mills_Bull%20Econ%20Geol%20.PDF |title=The role of bacteria in environmental geochemistry |last1=Mills |first1=A.L. |access-date=19 November 2017 |archive-date=6 April 2019 |archive-url=https://web.archive.org/web/20190406194730/https://lmecol.evsc.virginia.edu/pubs/C13-Mills_Bull%20Econ%20Geol%20.PDF |url-status=dead }}</ref> Heterotrophs function as [[Consumer (food chain)|consumers in food chain]]: they obtain these nutrients from [[Saprotrophic nutrition|saprotrophic]], [[Parasitic nutrition|parasitic]], or [[Holozoic nutrition|holozoic nutrients]].<ref>{{cite web |url=https://www.int-res.com/articles/meps/22/m022p101.pdf |archive-url=https://web.archive.org/web/20110524124225/http://www.int-res.com/articles/meps/22/m022p101.pdf |archive-date=2011-05-24 |url-status=live |title=Heterotrophic nutrition and control of bacterial density |access-date=19 November 2017}}</ref> They break down complex organic compounds (e.g., carbohydrates, fats, and proteins) produced by autotrophs into simpler compounds (e.g., carbohydrates into [[glucose]], fats into [[fatty acids]] and [[glycerol]], and proteins into [[amino 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. [[Fermentation|Fermenting]] heterotrophs are either facultative or obligate [[Anaerobic organism|anaerobes]] that carry out fermentation in low oxygen environments, in which the production of ATP is commonly coupled with [[substrate-level phosphorylation]] and the production of end products (e.g. alcohol, {{CO2}}, sulfide).<ref name=":0">{{cite book |title=Bacterial Metabolism |last1=Gottschalk |first1=Gerhard |year=2012 |publisher=Springer |isbn=978-0387961538 |edition=2 |doi=10.1007/978-1-4612-1072-6 |series=Springer Series in Microbiology |s2cid=32635137 |url-access=registration |url=https://archive.org/details/bacterialmetabol0000gott }}</ref> These products can then serve as the substrates for other bacteria in the [[Anaerobic digestion|anaerobic digest]], and be converted into CO<sub>2</sub> and CH<sub>4</sub>, which is an important step for the [[carbon cycle]] for removing organic fermentation products from anaerobic environments.<ref name=":0" /> Heterotrophs can undergo [[Cellular respiration|respiration]], in which ATP production is coupled with [[oxidative phosphorylation]].<ref name=":0" /><ref name=":2">{{cite book |title=MICB 201: Introductory Environmental Microbiology |last1=Wade |first1=Bingle |year=2016 |pages=236–250}}</ref> This leads to the release of oxidized carbon wastes such as CO<sub>2</sub> and reduced wastes like H<sub>2</sub>O, H<sub>2</sub>S, or N<sub>2</sub>O into the atmosphere. Heterotrophic microbes' respiration and fermentation account for a large portion of the release of CO<sub>2</sub> into the atmosphere, making it available for autotrophs as a source of nutrient and plants as a cellulose synthesis substrate.<ref name=":1">{{cite book |title=Processes in Microbial Ecology |last1=Kirchman |first1=David L. |year=2014 |publisher=Oxford University Press |place=Oxford |isbn=9780199586936|pages=79–98}}</ref><ref name=":2"/>

Respiration in heterotrophs is often accompanied by [[Mineralization (biology)|mineralization]], the process of converting organic compounds to inorganic forms.<ref name=":1" /> 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.<ref name=":1" /> S and N in organic carbon source are transformed into H<sub>2</sub>S and NH<sub>4</sub><sup>+</sup> through desulfurylation and [[deamination]], respectively.<ref name=":1" /><ref name=":2" /> Heterotrophs also allow for [[dephosphorylation]] as part of [[decomposition]].<ref name=":2" /> The conversion of N and S from organic form to inorganic form is a critical part of the [[Nitrogen cycle|nitrogen]] and [[sulfur cycle]]. H<sub>2</sub>S formed from desulfurylation is further oxidized by lithotrophs and phototrophs while NH<sub>4</sub><sup>+</sup> formed from deamination is further oxidized by lithotrophs to the forms available to plants.<ref name=":1" /><ref name=":2" /> Heterotrophs' ability to mineralize essential elements is critical to plant survival.<ref name=":2" />

Most [[opisthokont]]s and [[prokaryote]]s are heterotrophic; in particular, all animals and fungi are heterotrophs.<ref name="cell">{{cite web |url=http://highered.mcgraw-hill.com/sites/dl/free/0072965819/415836/rav65819_ch07.pdf |title=How Cells Harvest Energy |publisher=[[McGraw Hill Education|McGraw-Hill Higher Education]] |access-date=2010-10-10 |archive-url=https://web.archive.org/web/20120731144141/http://highered.mcgraw-hill.com/sites/dl/free/0072965819/415836/rav65819_ch07.pdf |archive-date=2012-07-31 |url-status=dead}}</ref> Some animals, such as [[coral]]s, form [[symbiosis|symbiotic]] relationships with autotrophs and obtain organic carbon in this way. Furthermore, some [[parasitic plant]]s have also turned fully or partially heterotrophic, while [[carnivorous plant]]s consume animals to augment their nitrogen supply while remaining autotrophic.

Animals are classified as heterotrophs by ingestion, fungi are classified as heterotrophs by absorption.

== Heterotroph Impacts on Biogeochemical Cycles ==
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.<ref>{{Cite journal |last=Duarte |first=Carlos M. |last2=Prairie |first2=Yves T. |date=2005-11-01 |title=Prevalence of Heterotrophy and Atmospheric CO2 Emissions from Aquatic Ecosystems |url=https://link.springer.com/article/10.1007/s10021-005-0177-4 |journal=Ecosystems |language=en |volume=8 |issue=7 |pages=862–870 |doi=10.1007/s10021-005-0177-4 |issn=1435-0629}}</ref> 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.<ref>{{Cite journal |last=Falkowski |first=Paul G. |last2=Fenchel |first2=Tom |last3=Delong |first3=Edward F. |date=2008-05-23 |title=The Microbial Engines That Drive Earth's Biogeochemical Cycles |url=https://www.science.org/doi/10.1126/science.1153213 |journal=Science |volume=320 |issue=5879 |pages=1034–1039 |doi=10.1126/science.1153213}}</ref>

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.<ref>{{Cite journal |last=Canfield |first=Donald E. |last2=Glazer |first2=Alexander N. |last3=Falkowski |first3=Paul G. |date=2010-10-08 |title=The Evolution and Future of Earth’s Nitrogen Cycle |url=https://www.science.org/doi/10.1126/science.1186120 |journal=Science |volume=330 |issue=6001 |pages=192–196 |doi=10.1126/science.1186120}}</ref> These processes can be known as secondary metabolism in heterotrophs.<ref>{{Cite journal |last=Martikainen |first=Pertti J. |date=2022-05-01 |title=Heterotrophic nitrification – An eternal mystery in the nitrogen cycle |url=https://linkinghub.elsevier.com/retrieve/pii/S0038071722000682 |journal=Soil Biology and Biochemistry |volume=168 |pages=108611 |doi=10.1016/j.soilbio.2022.108611 |issn=0038-0717|doi-access=free }}</ref> Heterotrophic microorganisms are essential in the mineralization of organic compounds containing nitrogen.<ref>{{Cite book |last=Werner |first=Dietrich |title=The Biology of Diatoms |publisher=University of California Press |year=1977 |pages=170-181}}</ref><ref>{{Cite book |last=Schlesinger |first=William H. |title=Biogeochemistry: an analysis of global change |last2=Bernhardt |first2=Emily S. |date=2020 |publisher=Academic Press, an imprint of Elsevier |isbn=978-0-12-814609-5 |edition=4th |location=Waltham, MA}}</ref> 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.<ref>{{Citation |last=Howarth |first=Robert W. |title=THE REGULATION OF DECOMPOSITION AND HETEROTROPHIC MICROBIAL ACTIVITY IN SALT MARSH SOILS: A REVIEW |date=1982-01-01 |work=Estuarine Comparisons |pages=183–207 |editor-last=Kennedy |editor-first=VICTOR S. |url=https://linkinghub.elsevier.com/retrieve/pii/B978012404070050017X |access-date=2025-04-22 |publisher=Academic Press |doi=10.1016/b978-0-12-404070-0.50017-x |isbn=978-0-12-404070-0 |last2=Hobbie |first2=John E.}}</ref> By decomposing dead organic matter, they release essential elements like phosphorus through dephosphorylation, making these nutrients available for other organisms.<ref>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.</ref> 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.<ref>{{Cite journal |last=Jørgensen |first=Bo Barker |last2=Boetius |first2=Antje |date=October 2007 |title=Feast and famine — microbial life in the deep-sea bed |url=https://www.nature.com/articles/nrmicro1745 |journal=Nature Reviews Microbiology |language=en |volume=5 |issue=10 |pages=770–781 |doi=10.1038/nrmicro1745 |issn=1740-1534}}</ref>

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.<ref>{{Cite journal |last=Tran |first=Ngoc Han |last2=Urase |first2=Taro |last3=Ngo |first3=Huu Hao |last4=Hu |first4=Jiangyong |last5=Ong |first5=Say Leong |date=2013-10-01 |title=Insight into metabolic and cometabolic activities of autotrophic and heterotrophic microorganisms in the biodegradation of emerging trace organic contaminants |url=https://linkinghub.elsevier.com/retrieve/pii/S0960852413011516 |journal=Bioresource Technology |volume=146 |pages=721–731 |doi=10.1016/j.biortech.2013.07.083 |issn=0960-8524}}</ref>

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.

== Impacts on Biogeochemical Cycles ==
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.<ref>{{Cite journal |last1=Falkowski |first1=Paul G. |last2=Fenchel |first2=Tom |last3=Delong |first3=Edward F. |date=2008-05-23 |title=The Microbial Engines That Drive Earth's Biogeochemical Cycles |url=https://www.science.org/doi/10.1126/science.1153213 |journal=Science |language=en |volume=320 |issue=5879 |pages=1034–1039 |doi=10.1126/science.1153213 |pmid=18497287 |bibcode=2008Sci...320.1034F |issn=0036-8075}}</ref>

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.<ref>{{Cite journal |last1=Canfield |first1=Donald E. |last2=Glazer |first2=Alexander N. |last3=Falkowski |first3=Paul G. |date=2010-10-08 |title=The Evolution and Future of Earth's Nitrogen Cycle |url=https://www.science.org/doi/10.1126/science.1186120 |journal=Science |language=en |volume=330 |issue=6001 |pages=192–196 |doi=10.1126/science.1186120 |pmid=20929768 |bibcode=2010Sci...330..192C |issn=0036-8075}}</ref> Heterotrophic microorganisms are essential in the mineralization of organic compounds containing nitrogen.<ref>{{Cite book |last1=Schlesinger |first1=William H. |title=Biogeochemistry: an analysis of global change |last2=Bernhardt |first2=Emily S. |date=2020 |publisher=Academic press, an imprint of Elsevier |isbn=978-0-12-814608-8 |edition=4th |location=London}}</ref> 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.<ref>{{Cite journal |last1=Jørgensen |first1=Bo Barker |last2=Boetius |first2=Antje |date=October 2007 |title=Feast and famine — microbial life in the deep-sea bed |url=https://www.nature.com/articles/nrmicro1745 |journal=Nature Reviews Microbiology |language=en |volume=5 |issue=10 |pages=770–781 |doi=10.1038/nrmicro1745 |pmid=17828281 |issn=1740-1526}}</ref>

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.<ref>{{Cite journal |last1=Wardle |first1=David A. |last2=Bardgett |first2=Richard D. |last3=Klironomos |first3=John N. |last4=Setälä |first4=Heikki |last5=van der Putten |first5=Wim H. |last6=Wall |first6=Diana H. |date=2004-06-11 |title=Ecological Linkages Between Aboveground and Belowground Biota |url=https://www.science.org/doi/10.1126/science.1094875 |journal=Science |volume=304 |issue=5677 |pages=1629–1633 |doi=10.1126/science.1094875|pmid=15192218 |bibcode=2004Sci...304.1629W }}</ref>

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.

==References==
{{reflist|25em}}

[[Category:Biology terminology]]
[[Category:Trophic ecology]]