Primary nutritional groups

{{short description|Group of organisms}} {{More citations needed|date=September 2010}} '''Primary nutritional groups''' are groups of organisms, divided according to the sources of energy, electrons, and carbon needed for living, growth, and reproduction. The sources of energy can be light or chemical compounds, the source of electrons can be organic or inorganic, and the sources of carbon can also be of organic or inorganic origin.<ref name="pmid17028233">{{cite journal |vauthors=Eiler A |title=Evidence for the ubiquity of mixotrophic bacteria in the upper ocean: implications and consequences |journal=Applied and Environmental Microbiology |volume=72 |issue=12 |pages=7431–7 |date=December 2006 |pmid=17028233 |pmc=1694265 |doi=10.1128/AEM.01559-06 |bibcode=2006ApEnM..72.7431E |quote=Table 1: Definitions of metabolic strategies to obtain carbon and energy}}</ref>.

The terms ''aerobic respiration'', ''anaerobic respiration'', and ''fermentation'' (''substrate-level phosphorylation'') do not refer to primary nutritional groups, but simply reflect the different use of possible electron acceptors in particular organisms, such as {{O2}} in aerobic respiration, nitrate ({{chem|NO|3|−}}) or sulfate ({{chem|SO|4|2−}}) in anaerobic respiration, or various metabolic intermediates in fermentation.

==Primary sources of energy== ''Phototrophs'' absorb light in photoreceptors and transform it into chemical energy. ''Chemotrophs'' directly absorb chemical energy from molecules.

The free energy is stored as potential energy in ATP, carbohydrates, or proteins. Eventually, the energy is used for life processes such as moving, growth, and reproduction.{{Citation needed|date=August 2025}}

Plants and some bacteria can alternate between phototrophy and chemotrophy, depending on the availability of light.<ref>{{Cite journal |last=Callister |first=Stephen J. |last2=Nicora |first2=Carrie D. |last3=Zeng |first3=Xiaohua |last4=Roh |first4=Jung Hyeob |last5=Dominguez |first5=Miguel A. |last6=Tavano |first6=Christine L. |last7=Monroe |first7=Matthew E. |last8=Kaplan |first8=Samuel |last9=Donohue |first9=Timothy J. |last10=Smith |first10=Richard D. |last11=Lipton |first11=Mary S. |date=2006-12-01 |title=Comparison of aerobic and photosynthetic Rhodobacter sphaeroides 2.4.1 proteomes |url=https://www.sciencedirect.com/science/article/pii/S0167701206001242 |journal=Journal of Microbiological Methods |volume=67 |issue=3 |pages=424–436 |doi=10.1016/j.mimet.2006.04.021 |issn=0167-7012|pmc=2794424}}</ref>{{Better source needed|reason=The current source provided is not up to date (WP:OLDSOURCES).|date=August 2025}}

==Primary sources of reducing equivalents==

''Organotrophs'' use organic compounds as electron/hydrogen donors. ''Lithotrophs'' use inorganic compounds as electron/hydrogen donors.

The electrons or hydrogen atoms from reducing equivalents (electron donors) are needed by both phototrophs and chemotrophs in reduction-oxidation reactions that transfer energy in the anabolic processes of ATP synthesis (in heterotrophs) or biosynthesis (in autotrophs). The electron or hydrogen donors are taken up from the environment.

Organotrophic organisms are often also heterotrophic, using organic compounds as sources of both electrons and carbon. Similarly, lithotrophic organisms are often also autotrophic, using inorganic sources of electrons and {{CO2}} as their inorganic carbon source.

Some lithotrophic bacteria can utilize diverse sources of electrons, depending on the availability of possible donors.

The organic or inorganic substances (e.g., oxygen) used as electron acceptors needed in the catabolic processes of aerobic or anaerobic respiration and fermentation are not taken into account here.

For example, plants are lithotrophs because they use water as their electron donor for the electron transport chain across the thylakoid membrane. Animals are organotrophs because they use organic compounds as electron donors to synthesize ATP (plants also do this, but this is not taken into account). Both use oxygen in respiration as an electron acceptor, but this character is not used to define them as lithotrophs.

==Primary sources of carbon==

''Heterotrophs'' metabolize organic compounds to obtain carbon for growth and development. ''Autotrophs'' use carbon dioxide ({{CO2}}) as their source of carbon.

==Energy and carbon== thumb|240px|right|Yellow fungus {| class="wikitable float-right" style="text-align:center" width="50%" |+Classification of organisms based on their metabolism |- | rowspan=2 bgcolor="#FFFF00" |Energy source || bgcolor="#FFFF00" |Light || bgcolor="#FFFF00" |photo- || rowspan=2 colspan=2 |  || rowspan=6 bgcolor="#7FC31C" |-troph |- | bgcolor="#FFFF00" |Molecules || bgcolor="#FFFF00" |chemo- |- | rowspan=2 bgcolor="#FFB300" |Electron donor || bgcolor="#FFB300" |Organic compounds || rowspan=2 |   || bgcolor="#FFB300" |organo- || rowspan=2 |   |- | bgcolor="#FFB300" |Inorganic compounds || bgcolor="#FFB300" |litho- |- | rowspan=2 bgcolor="#FB805F" |Carbon source || bgcolor="#FB805F" |Organic compounds || rowspan=2 colspan=2 |  || bgcolor="#FB805F" |hetero- |- | bgcolor="#FB805F" |Carbon dioxide || bgcolor="#FB805F" |auto- |} A ''chemoorganoheterotrophic'' organism is one that requires organic substrates to get its carbon for growth and development, and that obtains its energy from the decomposition of an organic compound. This group of organisms may be further subdivided according to what kind of organic substrate and compound they use. Decomposers are examples of chemoorganoheterotrophs which obtain carbon and electrons or hydrogen from dead organic matter. Herbivores and carnivores are examples of organisms that obtain carbon and electrons or hydrogen from living organic matter.

Chemoorganotrophs are organisms which use the chemical energy in organic compounds as their energy source and obtain electrons or hydrogen from the organic compounds, including sugars (i.e. glucose), fats, and proteins.<ref name="kt">{{cite web |url=http://textbookofbacteriology.net/nutgro.html |title=Todar's Online Textbook of Bacteriology |access-date=2014-04-19 |year=2009 |first=Kenneth |last=Todar |name-list-style=vanc |work=Nutrition and Growth of Bacteria}}</ref> Chemoheterotrophs also obtain the carbon atoms that they need for cellular function from these organic compounds.

All animals are chemoheterotrophs (meaning they oxidize chemical compounds as a source of energy and carbon), as are fungi, protozoa, and some bacteria. The important differentiation among this group is that chemoorganotrophs oxidize only organic compounds while chemolithotrophs instead use oxidation of inorganic compounds as a source of energy.<ref name="dk">{{cite book |vauthors=Kelly DP, Mason J, Wood A |chapter=Energy Metabolism in Chemolithotrophs |date=1987 |veditors=van Verseveld HW, Duine JA |title=Microbial Growth on C1 Compounds |pages=186–7 |publisher=Springer |doi=10.1007/978-94-009-3539-6_23 |isbn=978-94-010-8082-8}}</ref>

==Primary metabolism table== The following table gives some examples for each nutritional group:<ref>{{cite journal |vauthors=Lwoff A, Van Niel CB, Ryan TF, Tatum EL |title=Nomenclature of nutritional types of microorganisms. |journal=Cold Spring Harbor Symposia on Quantitative Biology |edition=5th |date=1946 |volume=11 |pages=302–3 |url=http://symposium.cshlp.org/content/11/local/back-matter.pdf}}</ref><ref>{{cite book |vauthors=Andrews JH |date=1991 |title=Comparative Ecology of Microorganisms and Macroorganisms |publisher=Springer |page=68 |url=https://books.google.com/books?id=4ZDhBwAAQBAJ |isbn=978-0-387-97439-2}}</ref><ref name="pmid23443991">{{cite journal |vauthors=Yafremava LS, Wielgos M, Thomas S, Nasir A, Wang M, Mittenthal JE, Caetano-Anollés G |title=A general framework of persistence strategies for biological systems helps explain domains of life |journal=Frontiers in Genetics |volume=4 |page=16 |date=2013 |pmid=23443991 |pmc=3580334 |doi=10.3389/fgene.2013.00016 |doi-access=free}}</ref><ref>{{cite book |veditors=Margulis L, McKhann HI, Olendzenski L |title=Illustrated Glossary of Protoctista: Vocabulary of the Algae, Apicomplexa, Ciliates, Foraminifera, Microspora, Water Molds, Slime Molds, and the Other Protoctists |publisher=Jones & Bartlett Learning |date=1993 |page=xxv |url=https://books.google.com/books?id=y55Efu3baksC |isbn=978-0-86720-081-2}}</ref> {| class="wikitable" |- ! Energy source ! Electron/ H-atom donor ! Carbon source ! Name ! Examples |- |rowspan="4" style="background: #ddffdd"| Sunlight ''Photo-'' |rowspan="2" style="background: #ffdfcc"| Organic ''-organo-'' |style="background: #ffbfbf"| Organic ''-heterotroph'' | Photoorganoheterotroph |Some bacteria (''Rhodobacter capsulatus'', Heliobacteria), and some archaea (Haloarchaea)<ref name="Morris 2019">Morris, J. et al. (2019). "Biology: How Life Works", 3rd edition, W. H. Freeman. {{ISBN|978-1319017637}}</ref> |- |style="background: #bfdfff"| Carbon dioxide ''-autotroph'' | Photoorganoautotroph |Some bacteria perform anoxygenic photosynthesis and fix atmospheric carbon (''Chloroflexia'') |- |rowspan="2" style="background: #dfbfff"| Inorganic ''-litho-''* |style="background: #ffbfbf"| Organic ''-heterotroph'' | Photolithoheterotroph |Purple non-sulfur bacteria |- |style="background: #bfdfff"| Carbon dioxide ''-autotroph'' | Photolithoautotroph | Some bacteria (cyanobacteria), some eukaryotes (eukaryotic algae, land plants). Photosynthesis. |- |rowspan="4" style="background: #ffdddd"| Breaking Chemical Compounds ''Chemo-'' |rowspan="2" style="background: #ffdfcc"| Organic ''-organo-'' |style="background: #ffbfbf"| Organic ''-heterotroph'' | Chemoorganoheterotroph | Predatory, parasitic, and saprophytic prokaryotes. Some eukaryotes (heterotrophic protists, fungi, animals)

|- |style="background: #bfdfff"| Carbon dioxide ''-autotroph'' | Chemoorganoautotroph | Some archaea (anaerobic methanotrophic archaea).<ref name="pmid23129626">{{cite journal |vauthors=Kellermann MY, Wegener G, Elvert M, Yoshinaga MY, Lin YS, Holler T, Mollar XP, Knittel K, Hinrichs KU |display-authors=6 |title=Autotrophy as a predominant mode of carbon fixation in anaerobic methane-oxidizing microbial communities |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=47 |pages=19321–6 |date=November 2012 |pmid=23129626 |pmc=3511159 |doi=10.1073/pnas.1208795109 |bibcode=2012PNAS..10919321K |doi-access=free}}</ref> Chemosynthesis, synthetically autotrophic ''Escherichia coli'' bacteria,<ref name=Gleizer19>{{cite journal |vauthors=Gleizer S, Ben-Nissan R, Bar-On YM, Antonovsky N, Noor E, Zohar Y, Jona G, Krieger E, Shamshoum M, Bar-Even A, Milo R |display-authors=6 |title=Conversion of Escherichia coli to Generate All Biomass Carbon from CO2 |journal=Cell |volume=179 |issue=6 |pages=1255–1263.e12 |date=November 2019 |pmid=31778652 |pmc=6904909 |doi=10.1016/j.cell.2019.11.009}}</ref> and ''Pichia pastoris'' yeast.<ref name=Gassler19>{{cite journal |vauthors=Gassler T, Sauer M, Gasser B, Egermeier M, Troyer C, Causon T, Hann S, Mattanovich D, Steiger MG |display-authors=6 |title=The industrial yeast ''Pichia pastoris'' is converted from a heterotroph into an autotroph capable of growth on CO2 |journal=Nature Biotechnology |volume=38 |issue=2 |pages=210–6 |date=December 2019 |pmid=31844294 |doi=10.1038/s41587-019-0363-0 |pmc=7008030}}</ref> |- |rowspan="2" style="background: #dfbfff"| Inorganic ''-litho-''* |style="background: #ffbfbf"| Organic ''-heterotroph'' | Chemolithoheterotroph |Some bacteria (''Oceanithermus profundus'')<ref name="pmid12807196">{{cite journal |vauthors=Miroshnichenko ML, L'Haridon S, Jeanthon C, Antipov AN, Kostrikina NA, Tindall BJ, Schumann P, Spring S, Stackebrandt E, Bonch-Osmolovskaya EA |display-authors=6 |title=''Oceanithermus profundus'' gen. nov., sp. nov., a thermophilic, microaerophilic, facultatively chemolithoheterotrophic bacterium from a deep-sea hydrothermal vent |journal=International Journal of Systematic and Evolutionary Microbiology |volume=53 |issue=Pt 3 |pages=747–52 |date=May 2003 |pmid=12807196 |doi=10.1099/ijs.0.02367-0 |doi-access=free}}</ref> |- |style="background: #bfdfff"| Carbon dioxide ''-autotroph'' | Chemolithoautotroph |Some bacteria (''Nitrobacter''), some archaea (''Methanobacteria''). Chemosynthesis. |}

<nowiki/>*Some authors use ''-hydro-'' when the source is water.

{{Wiktionary|-troph}} The common final part ''-troph'' is from Ancient Greek {{wikt-lang|grc|τροφή}} {{transliteration|grc|trophḗ}} "nutrition".

==Mixotrophs==

Some, usually unicellular, organisms can switch between different metabolic modes, for example between photoautotrophy, photoheterotrophy, and chemoheterotrophy in ''Chroococcales''.<ref>{{cite journal |vauthors=Rippka R |title=Photoheterotrophy and chemoheterotrophy among unicellular blue-green algae |journal=Archives of Microbiology |volume=87 |issue=1 |pages=93–98 |date=March 1972 |doi=10.1007/BF00424781 |s2cid=155161}}</ref> ''Rhodopseudomonas palustris'' – another example – can grow with or without oxygen, use either light, inorganic compounds, or organic compounds for energy.<ref>{{Cite journal |last1=Li |first1=Meijie |last2=Ning |first2=Peng |last3=Sun |first3=Yi |last4=Luo |first4=Jie |last5=Yang |first5=Jianming |date=2022 |title=Characteristics and Application of ''Rhodopseudomonas palustris'' as a Microbial Cell Factory |journal=Frontiers in Bioengineering and Biotechnology |volume=10 |article-number=897003 |doi=10.3389/fbioe.2022.897003 |pmid=35646843 |pmc=9133744 |issn=2296-4185 |doi-access=free}}</ref> Such mixotrophic organisms may dominate their habitat, due to their capability to use more resources than either photoautotrophic or organoheterotrophic organisms.<ref name="Eiler_2006">{{cite journal |vauthors=Eiler A |title=Evidence for the ubiquity of mixotrophic bacteria in the upper ocean: implications and consequences |journal=Applied and Environmental Microbiology |volume=72 |issue=12 |pages=7431–7 |date=December 2006 |pmid=17028233 |pmc=1694265 |doi=10.1128/AEM.01559-06 |bibcode=2006ApEnM..72.7431E}}</ref>

==Examples== All sorts of combinations may exist in nature, but some are more common than others. For example, most plants are ''photolithoautotrophic'', since they use light as an energy source, water as electron donor, and {{CO2}} as a carbon source. All animals and fungi are ''chemoorganoheterotrophic'', since they use organic substances both as chemical energy sources and as electron/hydrogen donors and carbon sources. Some eukaryotic microorganisms, however, are not limited to just one nutritional mode. For example, some algae live photoautotrophically in the light, but shift to chemoorganoheterotrophy in the dark. Even higher plants retained their ability to respire heterotrophically on starch at night which had been synthesised phototrophically during the day.

Prokaryotes show a great diversity of nutritional categories.<ref name="TangTangBlankenship 2011">{{cite journal |vauthors=Tang KH, Tang YJ, Blankenship RE |title=Carbon metabolic pathways in phototrophic bacteria and their broader evolutionary implications |journal=Front Microbiol |volume=2 |issue=? |page=165 |date=2011 |pmid=21866228 |pmc=3149686 |doi=10.3389/fmicb.2011.00165 |doi-access=free}}</ref> For example, cyanobacteria and many purple sulfur bacteria can be ''photolithoautotrophic'', using light for energy, {{H2O}} or sulfide as electron/hydrogen donors, and {{CO2}} as carbon source, whereas green non-sulfur bacteria can be ''photoorganoheterotrophic'', using organic molecules as both electron/hydrogen donors and carbon sources.<ref name="Morris 2019"/><ref name="TangTangBlankenship 2011"/> Many bacteria are ''chemoorganoheterotrophic'', using organic molecules as energy, electron/hydrogen, and carbon sources.<ref name="Morris 2019"/> Some bacteria are limited to only one nutritional group, whereas others are facultative and switch from one mode to the other, depending on the nutrient sources available.<ref name="TangTangBlankenship 2011"/> Sulfur-oxidizing, iron, and anammox bacteria as well as methanogens are ''chemolithoautotrophs'', using inorganic energy, electron, and carbon sources. ''Chemolithoheterotrophs'' are rare because heterotrophy implies the availability of organic substrates, which can also serve as easy electron sources, making lithotrophy unnecessary. ''Photoorganoautotrophs'' are uncommon since their organic source of electrons/hydrogens would provide an easy carbon source, resulting in heterotrophy.

Synthetic biology efforts enabled the transformation of the trophic mode of two model microorganisms from heterotrophy to chemoorganoautotrophy:

* ''Escherichia coli'' was genetically engineered and then evolved in the laboratory to use {{CO2}} as the sole carbon source while using the one-carbon molecule formate as the source of electrons.<ref name=Gleizer19/> * The methylotrophic ''Pichia pastoris'' yeast was genetically engineered to use {{CO2}} as the carbon source instead of methanol, while the latter remained the source of electrons for the cells.<ref name=Gassler19/>

==See also== {{Refbegin|35em}} * Autotroph * Chemosynthesis * Chemotroph * Heterotroph * Lithotroph * Metabolism * Mixotroph * Organotroph * Phototroph {{Refend}}

==Notes and references== {{Reflist|32em}}

Category:Physiology Category:Trophic ecology