Mixotroph

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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.

Possible combinations are photo- and chemotrophy, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic.[1] They can take advantage of different environmental conditions.[2]

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.[1] Some organisms have incomplete Calvin cycles, so they are incapable of fixing carbon dioxide and must use organic carbon sources.

Types of Mixotrophy[edit]

Organisms may employ mixotrophy obligately or facultatively.

  • Obligate mixotrophy: in order to support growth and maintenance, an organism must utilize both heterotrophic and autotrophic means.
  • Obligate autotrophy with facultative heterotrophy: Autotrophy alone is sufficient for growth and maintenance, but heterotrophy may be used as a supplementary strategy when autotrophic energy is not enough, for example, when light intensity is low.
  • Facultative autotrophy with obligate heterotrophy: Heterotrophy is sufficient for growth and maintenance, but autotrophy may be used to supplement, for example, when prey availability is very low.
  • Facultative mixotrophy: Maintenance and growth may be obtained by heterotrophic or autotrophic means alone, and mixotrophy is used only when necessary.[3]

In order 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,[4] there are four mixotrophic groups based on relative roles of phagotrophy and phototrophy.

  • A: Heterotrophy (phagotrophy) is the norm, and phototrophy is only used when prey concentrations are limiting.
  • B: Phototrophy is the dominant strategy, and phagotrophy is employed as a supplement when light is limiting.
  • C: Phototrophy results in substances for both growth and ingestion, phagotrophy is employed when light is limiting.
  • D: Phototrophy is most common nutrition type, phagotrophy only used during prolonged dark periods, when light is extremely limiting.

An alternative scheme by Stoeker[5] also takes into account the role of nutrients and growth factors, and includes mixotrophs who have a photosynthetic symbiont or who retain chloroplasts from their prey. This scheme characterizes mixotrophs by their efficiency.

  • Type 1: "Ideal Mixotrophs" who utilize prey and sunlight equally well
  • Type 2: Supplement phototrophic activity with food consumption
  • Type 3: Primarily heterotrophic, use phototrophic activity during times of very low prey abundance.[6]

Examples[edit]

Plants[edit]

Amongst plants, mixotrophy classically applies to carnivorous, hemi-parasitic and partially hetero-mycotrophic species. However, this could be extended to a higher number of clades as research proves that organic forms of nitrogen and phosphorus such as DNA, proteins, amino-acids or carbohydrates also are part of a number of plants' nutrient supplies.[13]

See also[edit]

Notes[edit]

  1. ^ 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. 
  2. ^ 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. doi:10.1007/s00442-006-0413-4. PMID 16568278. 
  3. ^ Schoonhoven, Erwin (January 19, 2000). "Ecophysiology of Mixotrophs" (PDF). Thesis. 
  4. ^ Jones, H.J.L. (1997). "A classification of mixotrophic protists based on their behaviour". Freshwater Biology 37: 35–43. 
  5. ^ Stoecker, D.K. (1998). "Conceptual models of mixotrophy in planktonic protists and some ecological and evolutionary implications". European Journal of Protistology 34: 281–290. 
  6. ^ Tarangkoon, Woraporn (29 April 2010). "Mixtrophic Protists among Marine Ciliates and Dinoflagellates: Distribution, Physiology and Ecology" (PDF). Thesis. 
  7. ^ Libes, Susan M. (2009). Introduction to marine biogeochemistry (2 ed.). Academic Press. p. 192. ISBN 978-0-7637-5345-0. 
  8. ^ Dworkin, Martin (2006). The Prokaryotes: Ecophysiology and biochemistry 2 (3rd ed.). Springer. p. 988. ISBN 978-0-387-25492-0. 
  9. ^ Lengeler, Joseph W.; Drews, Gerhart; Schlegel, Hans Günter (1999). Biology of the Prokaryotes. Georg Thieme Verlag. p. 238. ISBN 978-3-13-108411-8. 
  10. ^ 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. 
  11. ^ Friedrich, Cornelius G.; et al. (2007). "Redox Control of Chemotrophic Sulfur Oxidation of Paracoccus pantotrophus". Microbial Sulfur Metabolism. Springer. pp. 139–150.  PDF
  12. ^ Fabricius, Katharina (2015). "Mixotrophy in soft corals of the Great Barrier Reef". http://data.aims.gov.au/. Australian Institute of Marine Science. Retrieved 11 November 2015.  External link in |website= (help)
  13. ^ Schmidt, Susanne; John A. Raven; Chanyarat Paungfoo-Lonhienne (2013). "The mixotrophic nature of photosynthetic plants". Functional Plant Biology 40 (5): 425. doi:10.1071/FP13061. ISSN 1445-4408. Retrieved 2013-11-26. 

External links[edit]