Mixoplankton

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A mixoplankton is a mixotrophic plankton. That is, it is a plankton 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 mixoplankton comprise more than half of all microscopic plankton. [1] There are two types of mixoplankton: those with their own chloroplasts, and those with endosymbionts—and others that acquire them through kleptoplasty or by enslaving the entire phototrophic cell. [2]

Contents

Overview

Plankton have traditionally been categorized as producer, consumer, and recycler groups, but some plankton are able to benefit from more than just one trophic level. In this mixed trophic strategy—known as mixotrophy—organisms act as both producers and consumers, either at the same time or switching between modes of nutrition in response to ambient conditions. This makes it possible to use photosynthesis for growth when nutrients and light are abundant, but switch to eating phytoplankton, zooplankton or each other when growing conditions are poor. Mixotrophs are divided into two groups; constitutive mixotrophs (CMs) which are able to perform photosynthesis on their own, and non-constitutive mixotrophs (NCMs) which use phagocytosis to engulf phototrophic prey that are either kept alive inside the host cell, which benefits from its photosynthesis, or they digested, except for the plastids, which continue to perform photosynthesis (kleptoplasty). [3] Recognition of the importance of mixotrophy as an ecological strategy is increasing, [4] as well as the wider role this may play in marine biogeochemistry. [5] Studies have shown that mixotrophs are much more important for marine ecology than previously assumed and comprise more than half of all microscopic plankton. [6] [7] Their presence acts as a buffer that prevents the collapse of ecosystems during times with little to no light. [8]

The distinction between plants and animals often breaks down in very small organisms. Possible combinations are photo- and chemotrophy, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic. [9] They can take advantage of different environmental conditions. [10]

Recent studies of marine microzooplankton found 30–45% of the ciliate abundance was mixotrophic, and up to 65% of the amoeboid, foram and radiolarian biomass was mixotrophic. [11]

Phaeocystis is an important algal genus found as part of the marine phytoplankton around the world. It has a polymorphic life cycle, ranging from free-living cells to large colonies. [12] It has the ability to form floating colonies, where hundreds of cells are embedded in a gel matrix, which can increase massively in size during blooms. [13] As a result, Phaeocystis is an important contributor to the marine carbon [14] and sulfur cycles. [15] Phaeocystis species are endosymbionts to acantharian radiolarians. [16] [17]

Mixotrophic radiolarians
Phaeocystis symbionts within an acantharian host.png
Acantharian radiolarian hosts Phaeocystis symbionts
Ecomare - schuimalg strand (7037-schuimalg-phaeocystis-ogb).jpg
White Phaeocystis algal foam washing up on a beach

Mixoplankton combining phototrophy and heterotrophy

Mixotrophic plankton that combine phototrophy and heterotrophy – table based on Stoecker et al., 2017 [18]
General typesDescriptionExampleFurther examples
Bacterioplankton Photoheterotrophic bacterioplankton Cholera bacteria SEM.jpg Vibrio cholerae Roseobacter spp.
Erythrobacter spp.
Gammaproteobacterial clade OM60
Widespread among bacteria and archaea
Phytoplankton Called constitutive mixotrophs by Mitra et al., 2016. [19] Phytoplankton that eat: photosynthetic protists with inherited plastids and the capacity to ingest prey. Ochromonas.png Ochromonas species Ochromonas spp.
Prymnesium parvum
Dinoflagellate examples: Fragilidium subglobosum, Heterocapsa triquetra, Karlodinium veneficum, Neoceratium furca, Prorocentrum minimum
Zooplankton Called nonconstitutive mixotrophs by Mitra et al., 2016. [19] Zooplankton that are photosynthetic: microzooplankton or metazoan zooplankton that acquire phototrophy through chloroplast retentiona or maintenance of algal endosymbionts.
GeneralistsProtists that retain chloroplasts and rarely other organelles from many algal taxa Halteria.jpg Most oligotrich ciliates that retain plastidsa
Specialists1. Protists that retain chloroplasts and sometimes other organelles from one algal species or very closely related algal species Dinophysis acuminata.jpg Dinophysis acuminata Dinophysis spp.
Myrionecta rubra
2. Protists or zooplankton with algal endosymbionts of only one algal species or very closely related algal species Noctiluca scintillans varias.jpg Noctiluca scintillans Metazooplankton with algal endosymbionts
Most mixotrophic Rhizaria (Acantharea, Polycystinea, and Foraminifera)
Green Noctiluca scintillans
aChloroplast (or plastid) retention = sequestration = enslavement. Some plastid-retaining species also retain other organelles and prey cytoplasm.

Mixotrophic dinoflagellates

Dinoflagellates are eukaryotic plankton, existing in marine and freshwater environments. Previously, dinoflagellates had been grouped into two categories, phagotrophs and phototrophs. [20] Mixotrophs, however include a combination of phagotrophy and phototrophy. [21] Mixotrophic dinoflagellates are a sub-type of planktonic dinoflagellates and are part of the phylum Dinoflagellata. [21] They are flagellated eukaryotes that combine photoautotrophy when light is available, and heterotrophy via phagocytosis. Dinoflagellates are one of the most diverse and numerous species of phytoplankton, second to diatoms.

Dinoflagellates have long whip-like structures called flagella that allow them to move freely throughout the water column. They are mainly marine but can also be found in freshwater environments. Combinations of phototrophy and phagotrophy allow organisms to supplement their inorganic nutrient uptake [22] This means an increased trophic transfer to higher levels in food web compared to the traditional food web. [22]

Mixotrophic dinoflagellates have the ability to thrive in changing ocean environments, resulting in shifts in red tide phenomenon and paralytic shellfish poisoning. [22] It is unknown as to how many species of dinoflagellates have mixotrophic capabilities, as this is a relatively new feeding-mechanism discovery.

References

  1. ↑ Richard Collins (14 November 2016). "Beware the mixotrophs – they can destroy entire ecosystems 'in a matter of hours'". Irish Examiner.
  2. ↑ "Microscopic body snatchers infest our oceans". Phys.org. 2 August 2017.
  3. ↑ Leles, Suzana Gonçalves (November 2018). "Modelling mixotrophic functional diversity and implications for ecosystem function - Oxford Journals" . Journal of Plankton Research. 40 (6): 627–642. doi:10.1093/plankt/fby044.
  4. ↑ Hartmann, M.; Grob, C.; Tarran, G.A.; Martin, A.P.; Burkill, P.H.; Scanlan, D.J.; Zubkov, M.V. (2012). "Mixotrophic basis of Atlantic oligotrophic ecosystems". Proc. Natl. Acad. Sci. USA. 109 (15): 5756–5760. Bibcode:2012PNAS..109.5756H. doi: 10.1073/pnas.1118179109 . PMC   3326507 . PMID   22451938.
  5. ↑ Ward, B.A.; Follows, M.J. (2016). "Marine mixotrophy increases trophic transfer efficiency, mean organism size, and vertical carbon flux". Proc. Natl. Acad. Sci. USA. 113 (11): 2958–2963. Bibcode:2016PNAS..113.2958W. doi: 10.1073/pnas.1517118113 . PMC   4801304 . PMID   26831076.
  6. ↑ "Mixing It Up in the Web of Life". The Scientist Magazine. Archived from the original on 21 January 2021.
  7. ↑ "Uncovered: the mysterious killer triffids that dominate life in our oceans". 3 November 2016.
  8. ↑ "Catastrophic Darkness". Astrobiology Magazine. Archived from the original on 26 September 2015. Retrieved 27 November 2019.
  9. ↑ 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. Bibcode:2006ApEnM..72.7431E. doi:10.1128/AEM.01559-06. PMC   1694265 . PMID   17028233.
  10. ↑ 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.
  11. ↑ Leles SG, Mitra A, Flynn KJ, Stoecker DK, Hansen PJ, Calbet A, McManus GB, Sanders RW, Caron DA, Not F, Hallegraeff GM (2017). "Oceanic protists with different forms of acquired phototrophy display contrasting biogeographies and abundance". Proceedings of the Royal Society B: Biological Sciences. 284 (1860): 20170664. doi:10.1098/rspb.2017.0664. PMC   5563798 . PMID   28768886.
  12. ↑ Schoemann, Véronique; Becquevort, Sylvie; Stefels, Jacqueline; Rousseau, Véronique; Lancelot, Christiane (1 January 2005). "Phaeocystis blooms in the global ocean and their controlling mechanisms: a review". Journal of Sea Research. Iron Resources and Oceanic Nutrients – Advancement of Global Environmental Simulations. 53 (1–2): 43–66. Bibcode:2005JSR....53...43S. CiteSeerX   10.1.1.319.9563 . doi:10.1016/j.seares.2004.01.008.
  13. ↑ "Welcome to the Phaeocystis antarctica genome sequencing project homepage".
  14. ↑ DiTullio, G. R.; Grebmeier, J. M.; Arrigo, K. R.; Lizotte, M. P.; Robinson, D. H.; Leventer, A.; Barry, J. P.; VanWoert, M. L.; Dunbar, R. B. (2000). "Rapid and early export of Phaeocystis antarctica blooms in the Ross Sea, Antarctica". Nature. 404 (6778): 595–598. Bibcode:2000Natur.404..595D. doi:10.1038/35007061. PMID   10766240. S2CID   4409009.
  15. ↑ J, Stefels; L, Dijkhuizen; WWC, Gieskes (20 July 1995). "DMSP-lyase activity in a spring phytoplankton bloom off the Dutch coast, related to Phaeocystis sp. abundance" (PDF). Marine Ecology Progress Series. 123: 235–243. Bibcode:1995MEPS..123..235S. doi: 10.3354/meps123235 .
  16. ↑ Decelle, Johan; Simó, Rafel; Galí, Martí; Vargas, Colomban de; Colin, Sébastien; Desdevises, Yves; Bittner, Lucie; Probert, Ian; Not, Fabrice (30 October 2012). "An original mode of symbiosis in open ocean plankton". Proceedings of the National Academy of Sciences. 109 (44): 18000–18005. Bibcode:2012PNAS..10918000D. doi: 10.1073/pnas.1212303109 . ISSN   0027-8424. PMC   3497740 . PMID   23071304.
  17. ↑ Mars Brisbin, Margaret; Grossmann, Mary M.; Mesrop, Lisa Y.; Mitarai, Satoshi (2018). "Intra-host Symbiont Diversity and Extended Symbiont Maintenance in Photosymbiotic Acantharea (Clade F)". Frontiers in Microbiology. 9: 1998. doi: 10.3389/fmicb.2018.01998 . ISSN   1664-302X. PMC   6120437 . PMID   30210473.
  18. ↑ Stoecker, D.K.; Hansen, P.J.; Caron, D.A.; Mitra, A. (2017). "Mixotrophy in the marine plankton". Annual Review of Marine Science. 9: 311–335. Bibcode:2017ARMS....9..311S. doi: 10.1146/annurev-marine-010816-060617 . PMID   27483121.
  19. 1 2 Mitra, A; Flynn, KJ; Tillmann, U; Raven, J; Caron, D; et al. (2016). "Defining planktonic protist functional groups on mechanisms for energy and nutrient acquisition; incorporation of diverse mixotrophic strategies". Protist. 167 (2): 106–20. doi: 10.1016/j.protis.2016.01.003 . hdl: 10261/131722 . PMID   26927496.
  20. ↑ Yoo, Yeong Du; Jeong, Hae Jin; Kang, Nam Seon; Song, Jae Yoon; Kim, Kwang Young; Lee, Gitack; Kim, Juhyoung (1 March 2010). "Feeding by the newly described mixotrophic dinoflagellate Paragymnodinium shiwhaense: feeding mechanism, prey species, and effect of prey concentration". The Journal of Eukaryotic Microbiology. 57 (2): 145–158. doi:10.1111/j.1550-7408.2009.00448.x. ISSN   1550-7408. PMID   20487129. S2CID   6312832.
  21. 1 2 Stoecker, Diane K. (1 July 1999). "Mixotrophy among Dinoflagellates1". Journal of Eukaryotic Microbiology. 46 (4): 397–401. doi:10.1111/j.1550-7408.1999.tb04619.x. ISSN   1550-7408. S2CID   83885629.
  22. 1 2 3 Mitra, A.; et al. (2014). "The role of mixotrophic protists in the biological carbon pump". Biogeosciences. 11 (4): 995–1005. Bibcode:2014BGeo...11..995M. doi: 10.5194/bg-11-995-2014 . hdl: 10453/117781 .
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