Heterotroph
A heterotroph (
Heterotrophs may be subdivided according to their energy source. If the heterotroph uses chemical energy, it is a
Heterotrophs represent one of the two mechanisms of nutrition (
Types
Heterotrophs can be
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
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.[10] 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.[15] This applies not only to animals and fungi but also to bacteria.[10]
Origin and diversification
The chemical
The theory of a chemical origin of life beginning with heterotrophic life was first proposed in 1924 by Alexander Ivanovich Oparin, and eventually published “The Origin of Life.” [20] It was independently proposed for the first time in English in 1929 by John Burdon Sanderson Haldane.[21] 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).[22]
Evidence grew to support this theory in 1953, when Stanley Miller conducted an experiment in which he added gasses that were thought to be present on early 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.[23] 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.[16] This experiment heralded the beginning of the field of synthetic prebiotic chemistry, and is now known as the Miller–Urey experiment.[24]
On early Earth, oceans and shallow waters were rich with organic molecules that could have been used by primitive heterotrophs.[25] 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.[25][26] 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.[27] Eventually, autotrophic and heterotrophic cells were engulfed by these early heterotrophs and formed a symbiotic relationship.[27] The endosymbiosis of autotrophic cells is suggested to have evolved into the chloroplasts while the endosymbiosis of smaller heterotrophs developed into the mitochondria, allowing the differentiation of tissues and development into multicellularity. This advancement allowed the further diversification of heterotrophs.[27] Today, many heterotrophs and autotrophs also utilize mutualistic relationships that provide needed resources to both organisms.[28] 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.[29]
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.[30] Simple biomolecules transported from space was considered to have been either too reduced to have been fermented or too heterogeneous to support microbial growth.[31] Heterotrophic microbes likely originated at low H2 partial pressures. Bases, amino acids, and ribose are considered to be the first fermentation substrates.[32]
Heterotrophs are currently found in each domain of life:
Flowchart
- Autotroph
- Chemoautotroph
- Photoautotroph
- Heterotroph
- Chemoheterotroph
- Photoheterotroph
Ecology
Many heterotrophs are
They can catabolize organic compounds by respiration, fermentation, or both. Fermenting heterotrophs are either facultative or obligate 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).[38] These products can then serve as the substrates for other bacteria in the anaerobic digest, and be converted into CO2 and CH4, which is an important step for the carbon cycle for removing organic fermentation products from anaerobic environments.[38] Heterotrophs can undergo respiration, in which ATP production is coupled with oxidative phosphorylation.[38][39] 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.[40][39]
Respiration in heterotrophs is often accompanied by
Most opisthokonts and prokaryotes are heterotrophic; in particular, all animals and fungi are heterotrophs.[5] Some animals, such as corals, form symbiotic relationships with autotrophs and obtain organic carbon in this way. Furthermore, some parasitic plants have also turned fully or partially heterotrophic, while carnivorous 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.
References
- ^ "heterotroph". Dictionary.com Unabridged (Online). n.d.
- ^ "heterotroph". Merriam-Webster.com Dictionary.
- ^ "Heterotroph Definition". Biology Dictionary. April 28, 2017. Retrieved 2023-12-02.
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- ^ a b "How Cells Harvest Energy" (PDF). McGraw-Hill Higher Education. Archived from the original (PDF) on 2012-07-31. Retrieved 2010-10-10.
- ^ Lwoff, A.; C.B. van Niel; P.J. Ryan; E.L. Tatum (1946). Nomenclature of nutritional types of microorganisms (PDF). Cold Spring Harbor Symposia on Quantitative Biology. Vol. XI (5th ed.). Cold Spring Harbor, N.Y.: The Biological Laboratory. pp. 302–303. Archived (PDF) from the original on 2017-11-07.
- ^ Wetzel, R.G. (2001). Limnology: Lake and river ecosystems (3rd ed.). Academic Press. p. 700.
- ^ "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 296.[full citation needed]
- ISBN 978-1-62949-013-7. Retrieved 9 October 2017.
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- ^ Mills, A.L. "The role of bacteria in environmental geochemistry" (PDF). Retrieved 19 November 2017.
- ^ "Heterotrophic nutrition and control of bacterial density" (PDF). Archived (PDF) from the original on 2011-05-24. Retrieved 19 November 2017.
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- ^ a b c d e f Wade, Bingle (2016). MICB 201: Introductory Environmental Microbiology. pp. 236–250.
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