Corallochytrium

Corallochytrium
Scientific classification
Domain:
Eukaryota
(unranked):
(unranked):
Phylum:
Class:
Cavalier-Smith 1995
Order:
Corallochytrida

Cavalier-Smith 1995
Family:
Corallochytridae
Genus:
Corallochytrium
Type species
Corallochytrium limacisporum[1]
Species

Corallochytrium confervae
Corallochytrium limacisporum

Introduction

Corallochytrium is a genus of choanoflagellates composed of a single aquatic species: C. limacisporum. The genus was first discovered and named in the Arabian sea’s coral lagoons by Kaghu-Kumar in 1987. It was first thought to be a member of the fungi-like thraustochytrids, however this was later disproven due to Corallochytriums lack of cilia and sagenogenetosome. Little research has been done on the life cycle or morphology. Most research concerning this genus has been done to uncover the evolution of animals and fungi, as Corallochytrium possess both animal and fungal enzymatic trademarks (C-14 reductase and α-AAR respectively).

Higher order taxa

KingdomOpisthokonta
PhylumChoanozoa
ClassCorallochytrea
OrderCorallochytrida
FamilyCorallochytridae
GenusCorallochytrium

Etymology

Corallochytrium limacisporum, the single species of the genus Corallochytrium. The genus name is derived from the habitat in which it was first found: coral reef lagoons (Raghu-kumar, 1987). The single species name is derived from the limax-shaped (slug-shaped) spores that are produced by the cell. Hence the name C. limacisporum (Raghu-kumar, 1987).

History of knowledge

C. limacisporum was first discovered and named in 1987 in coral reef lagoons of three Lakshadweep islands in the Arabian sea; Agatti, Kavartti and Bingaram (Raghu-kumar, 1987). The organism was initially thought to be a new thraustochytrid protist, a group of protists that closely resemble fungi and produce filaments from which they absorb nutrient (Raghu-kumar 1987). However, Cavalier-Smith & Allsopp (1996) explain that C. limancisporum had been wrongly classified as it lacks all defining characteristics of thraustochytrids. After phylogenetic analysis, Corallochytrium was determined not to be a thraustochytrid, but rather related to choanoflagellates. Cavalier-Smith assigned a new order and class for Corallochytrium under the phylum Choanozoa: Corallochytrida and Corallochytrea respectively (Cavelier-Smith 1995). Recently, Torruella et al. (2015) suggest that Corallochytrium has a sister group: Ichthyosporea, an early branching lineage leading to multi-cellular animals (Marshall, 2014) .

Habitat and ecology

Little research has been done considering Corallochytrium’s feeding and ecology, however its feeding regime has strong implications for the evolution of animals and fungi. Corallochytrium is a marine protist that inhabits coral reef lagoons in the Arabian sea (Raghu-kumar, 1987). C. limacisporum is predatory and feeds on large eukaryotic prey (Hehenberger et al. 2017). Corallochytrium has the fungal signature α-aminoadipate reductase (α-AAR) which is involved in the α-aminoadipate (AAA) pathway that synthesises amino acids from inorganic nitrogen in fungi (Sumathi et al. 2006). α-AAR is an evolutionarily conserved enzyme in the fungi (Sumathi at al., 2006).. The presence of α-AAR in Corallochytrium suggests it is a sister clade to fungi. Like fungi, Corallochytrium has also been found to be saprotrophic (Cavalier-Smith & Allsopp, 1996). Interestingly Coralochytrium also possess the sterol C-14 reductase gene involved in animal and fungi sterol pathways (Sumathi at al., 2006).

Description

Morphology

Corallochytrium is a small (around 5-20μm in diameter), round, non-photosynthetic choanoflagellate (Torruella et al. 2015, Cavalier-Smith & Allsopp, 1996). It possesses no cilia (despite being a choanoflagellate) and no sagenogenetosome (Cavalier-Smith, 2001). It has a thin wall of unknown composition, that does not resemble that of fungi (Cavalier-Smith,2001 ). Like fungi and choanoflagellates, Corallochytrium has flat mitochondrial cristae (Cavalier-Smith, 2001).

Life cycle

Little documentation of the Corallochytrium life cycle exists. However it is known that Corallochytrium produces colonies by binary, palintomic cell division (Raghu-kumar, 1987). Completion of the Corallochytrium life cycle involves the release of limax-shaped spores (Raghu-kumar, 1987).

Practical importance

Corallochytrium has become an important species in unraveling the diversification of animals from fungi and opisthokont evolution. Corallochytrium and Ichthyosporea are thought to be the earliest branches of the holozoans (animals and all their ancestors, excluding fungi) (Torruella et al. 2015). However new phylogenetic trees placing Corallochytrium closer to fungi are emerging (Sumanthi et al. 2006). Phylogenetic trees based on the α-AAR gene, put Corallochytrium as a sister group to fungi, however trees using other genes, such as C-14 reductase, have been inconclusive in their placement in relation to animals or fungi (Sumanthi et al. 2006).

Taxonomy

SpeciesAuthor
Corallochytrium limacisporumRaghu-Kumar (1987)

References

  1. Ruiz-Trillo, Iñaki; Donachie, Stuart; Sitjà-Bobadilla, Ariadna; Roger, Andrew J.; Paley, Richard; Nichols, Krista M.; Whipps, Christopher M.; Pérez-Cordón, Gregorio; Eme, Laura (2015-09-21). "Phylogenomics Reveals Convergent Evolution of Lifestyles in Close Relatives of Animals and Fungi". Current Biology. 25 (18): 2404–2410. doi:10.1016/j.cub.2015.07.053. ISSN 0960-9822. PMID 26365255.
  • Cavalier-Smith, T. 2001.“What are Fungi” in The Mycota VIII: 3-30.
  • Cavalier-Smith, T., Allsopp, P. 1996. Corallochytrium, an enigmatic non-flagellate protozoan related to choanoflagellates. Protistology. 32(3): 306-310. doi: 10.1016/S0932-4739(96)80053-8
  • Hehenberger et al. 2017. Novel predators reshape holozoan phylogeny and reveal the presence of a two-component signaling system in the ancestor of animals. Current Biol. 27: 2043-2050. doi: 10.1016/j.cub.2017.06.006
  • “Chytrium”. Merriam-Webster. retrieved from: https://www.merriam-webster.com/dictionary/Chytrium
  • Marshall, W. 2014. Ichythyosporea. Mesomycetozoa, Mesomycetozoa. Version 06 December 2014 (under construction). Retrieved from: http://tolweb.org/Ichthyosporea/121172/2014.12.06 in Tree of Life Web Project.
  • Raghu-kumar, S. 1987. Occurrence of the Thraustochytrid, Corallochytrium limacisporum gen. et sp. nov. in the coral reef lagoons of the Lakshadweep Islands in the Arabian Sea. Botanica Marina. 30: 83-89. doi: 10.1515/botm.1987.30.1.83
  • Sumathi, J.C., Raghukumar, S., Kasbekar, D.P., Raghukumar, C. 2006. Molecular evidence of fungal signatures in the marine protist Corallochytrium limacisporum and its implications in the evolution of animals and fungi. Protist. 157(4): 363-373. doi: 10.1016/j.protis.2006.05.003
  • Torruella et al. 2015. Phylogenomics reveal convergent evolution of lifestyles in close relatives of animals and fungi. Current Biology. 25(18): 2404-2410. doi: 10.1016/j.cub.2015.07.053
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