A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. It is estimated that mixotrophs comprise more than half of all microscopic plankton.[1] There are two types of eukaryotic mixotrophs: those with their own chloroplasts, and those with endosymbionts—and those that acquire them through kleptoplasty or by enslaving the entire phototrophic cell.[2]

Possible combinations are photo- and chemotrophy, litho- and organotrophy (osmotrophy, phagotrophy and myzocytosis), auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic.[3] They can take advantage of different environmental conditions.[4]

If a trophic mode is obligate, then it is always necessary for sustaining growth and maintenance; if facultative, it can be used as a supplemental source.[3] Some organisms have incomplete Calvin cycles, so they are incapable of fixing carbon dioxide and must use organic carbon sources.

Overview

Organisms may employ mixotrophy obligately or facultatively.

Plants

A mixotrophic plant using mycorrhizal fungi to obtain photosynthesis products from other plants
A mixotrophic plant using mycorrhizal fungi to obtain photosynthesis products from other plants

Amongst plants, mixotrophy classically applies to carnivorous, hemi-parasitic and myco-heterotrophic species. However, this characterisation as mixotrophic could be extended to a higher number of clades as research demonstrates that organic forms of nitrogen and phosphorus — such as DNA, proteins, amino-acids or carbohydrates — are also part of the nutrient supplies of a number of plant species.[6]

Animals

Mixotrophy is less common among animals than among plants and microbes, but there are many examples of mixotrophic invertebrates and at least one example of a mixotrophic vertebrate.

Microorganisms

See also: Marine mixotrophs and Mixotrophic dinoflagellate

Bacteria and archaea

Protists

Traditional classification of mixotrophic protists In this diagram, types in open boxes as proposed by Stoecker [18] have been aligned against groups in grey boxes as proposed by Jones.[19][20]                              DIN = dissolved inorganic nutrients
Traditional classification of mixotrophic protists
In this diagram, types in open boxes as proposed by Stoecker [18] have been aligned against groups in grey boxes as proposed by Jones.[19][20]
                              DIN = dissolved inorganic nutrients

To characterize the sub-domains within mixotrophy, several very similar categorization schemes have been suggested. Consider the example of a marine protist with heterotrophic and photosynthetic capabilities: In the breakdown put forward by Jones,[19] there are four mixotrophic groups based on relative roles of phagotrophy and phototrophy.

An alternative scheme by Stoeker[18] also takes into account the role of nutrients and growth factors, and includes mixotrophs that have a photosynthetic symbiont or who retain chloroplasts from their prey. This scheme characterizes mixotrophs by their efficiency.

Another scheme, proposed by Mitra et al., specifically classifies marine planktonic mixotrophs so that mixotrophy can be included in ecosystem modeling.[20] This scheme classified organisms as:


Pathways used by Mitra et al. to derive functional groups of planktonic protists [20]
Levels in complexity among those different types of protists, according to Mitra et al.[20]
(A) phagotrophic (no phototrophy); (B) phototrophic (no phagotrophy); (C) constitutive mixotroph, with innate capacity for phototrophy; (D) generalist non-constitutive mixotroph acquiring photosystems from different phototrophic prey; (E) specialist non-constitutive mixotroph acquiring plastids from a specific prey type; (F) specialist non-constitutive mixotroph acquiring photosystems from endosymbionts. DIM = dissolved inorganic material (ammonium, phosphate etc.).                               DOM = dissolved organic material

See also

Notes

  1. ^ Beware the mixotrophs - they can destroy entire ecosystems 'in a matter of hours'
  2. ^ Microscopic body snatchers infest our oceans - Phys.org
  3. ^ a b Eiler A (December 2006). "Evidence for the Ubiquity of Mixotrophic Bacteria in the Upper Ocean: Implications and Consequences". Appl Environ Microbiol. 72 (12): 7431–7. doi:10.1128/AEM.01559-06. PMC 1694265. PMID 17028233.
  4. ^ Katechakis A, Stibor H (July 2006). "The mixotroph Ochromonas tuberculata may invade and suppress specialist phago- and phototroph plankton communities depending on nutrient conditions". Oecologia. 148 (4): 692–701. Bibcode:2006Oecol.148..692K. doi:10.1007/s00442-006-0413-4. PMID 16568278. S2CID 22837754.
  5. ^ Schoonhoven, Erwin (January 19, 2000). "Ecophysiology of Mixotrophs" (PDF). Thesis.
  6. ^ Schmidt, Susanne; John A. Raven; Chanyarat Paungfoo-Lonhienne (2013). "The mixotrophic nature of photosynthetic plants". Functional Plant Biology. 40 (5): 425–438. doi:10.1071/FP13061. ISSN 1445-4408. PMID 32481119.
  7. ^ Petherick, Anna (2010-07-30). "A solar salamander". Nature: news.2010.384. doi:10.1038/news.2010.384. ISSN 0028-0836.
  8. ^ Frazer, Jennifer (May 18, 2018). "Algae Living inside Salamanders Aren't Happy about the Situation". Scientific American Blog Network.
  9. ^ Burns, John A; Zhang, Huanjia; Hill, Elizabeth; Kim, Eunsoo; Kerney, Ryan (2 May 2017). "Transcriptome analysis illuminates the nature of the intracellular interaction in a vertebrate-algal symbiosis". eLife. 6. doi:10.7554/eLife.22054. PMC 5413350. PMID 28462779.
  10. ^ Compère, Pierre (November 1999). "Report of the Committee for Algae: 6". Taxon. 48 (1): 135–136. JSTOR 1224630.
  11. ^ Plotkin, Hod, Zaban; et al. (2010). "Solar energy harvesting in the epicuticle of the oriental hornet (Vespa orientalis)". Naturwissenschaften. 97 (12): 1067–1076. Bibcode:2010NW.....97.1067P. doi:10.1007/s00114-010-0728-1. PMID 21052618. S2CID 14022197.((cite journal)): CS1 maint: multiple names: authors list (link)
  12. ^ Djeghri, Nicolas; Pondaven, Philippe; Stibor, Herwig; Dawson, Michael N. (2019). "Review of the diversity, traits, and ecology of zooxanthellate jellyfishes" (PDF). Marine Biology. 166 (11). doi:10.1007/s00227-019-3581-6. S2CID 208553146.
  13. ^ Libes, Susan M. (2009). Introduction to marine biogeochemistry (2 ed.). Academic Press. p. 192. ISBN 978-0-7637-5345-0.
  14. ^ Dworkin, Martin (2006). The Prokaryotes: Ecophysiology and biochemistry. Vol. 2 (3rd ed.). Springer. p. 988. ISBN 978-0-387-25492-0.
  15. ^ Lengeler, Joseph W.; Drews, Gerhart; Schlegel, Hans Günter (1999). Biology of the Prokaryotes. Georg Thieme Verlag. p. 238. ISBN 978-3-13-108411-8.
  16. ^ Bartosik D, Sochacka M, Baj J (July 2003). "Identification and Characterization of Transposable Elements of Paracoccus pantotrophus". J Bacteriol. 185 (13): 3753–63. doi:10.1128/JB.185.13.3753-3763.2003. PMC 161580. PMID 12813068.
  17. ^ Friedrich, Cornelius G.; et al. (2007). "Redox Control of Chemotrophic Sulfur Oxidation of Paracoccus pantotrophus". Microbial Sulfur Metabolism. Springer. pp. 139–150.[permanent dead link] PDF[dead link]
  18. ^ a b Stoecker, Diane K. (1998). "Conceptual models of mixotrophy in planktonic protists and some ecological and evolutionary implications". European Journal of Protistology. 34 (3): 281–290. doi:10.1016/S0932-4739(98)80055-2.
  19. ^ a b Jones, Harriet (1997). "A classification of mixotrophic protists based on their behaviour". Freshwater Biology. 37: 35–43. doi:10.1046/j.1365-2427.1997.00138.x.
  20. ^ a b c d Mitra, Aditee; Flynn, Kevin J.; Tillmann, Urban; Raven, John A.; Caron, David; Stoecker, Diane K.; Not, Fabrice; Hansen, Per J.; Hallegraeff, Gustaaf; Sanders, Robert; Wilken, Susanne; McManus, George; Johnson, Mathew; Pitta, Paraskevi; Våge, Selina; Berge, Terje; Calbet, Albert; Thingstad, Frede; Jeong, Hae Jin; Burkholder, Joann; Glibert, Patricia M.; Granéli, Edna; Lundgren, Veronica (2016). "Defining Planktonic Protist Functional Groups on Mechanisms for Energy and Nutrient Acquisition: Incorporation of Diverse Mixotrophic Strategies". Protist. 167 (2): 106–120. doi:10.1016/j.protis.2016.01.003. PMID 26927496.
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  21. ^ Tarangkoon, Woraporn (29 April 2010). "Mixtrophic Protists among Marine Ciliates and Dinoflagellates: Distribution, Physiology and Ecology" (PDF). Thesis.[permanent dead link]