Helkesida (formerly known as Sainouroidea)[1] is a group of microscopic protists belonging to the supergroup Rhizaria, both discovered through molecular phylogenetic analyses. It contains amoeboid flagellates with two flagella. They are either free-living, mostly on fecal matter, or live inside the gut of animals. Among these amoebae, one lineage has independently evolved aggregative multicellularity similarly to slime moulds.[3]
| Helkesida | |
|---|---|
Scientific classification 
| |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Phylum: | Cercozoa |
| Superclass: | Eoglissa |
| Class: | Helkesea Cavalier-Smith 2018 |
| Order: | Helkesida Cavalier-Smith 2018[1] |
| Families[1][2] | |
| Diversity | |
| 24 species | |
Biology
editThe organisms classified as Helkesida commonly have a gliding motility in which the cells glide on their posterior flagellum. They are ancestrally amoeboid bi-flagellates without scales or theca.[2] Unlike most Cercozoa which have tubular mitochondrial cristae, they can also present flat cristae or discoid cristae. They are the only group within Rhizaria that present discoid mitochondrial cristae.[4]
These organisms have an amorphous apical centrosome attached to the nucleus by a rhizoplast. The kinetid arises from 2–4 very short centrioles with dense fibrous roots that attach them to each other and to the nucleus. Their anterior flagellum is reduced to a stub without its 9+2 axoneme. The centrosome also generates numerous microtubules in larger cells. The Golgi apparatus is seen attached to the nuclear envelope and the anterior rhizoplast. They have a microbody attached to the posterior end of the nucleus.[5]
One helkesid genus, Guttulinopsis, represents an independent lineage in which aggregative multicellularity has evolved to generate "fungi-like" fruiting bodies called sorocarps, similarly to slime moulds such as Dictyostelium.[4]
Ecology
editThe helkesid amoebae are bacterivores that can be free-living, mostly associated to fecal environments, or endozoic, associated to animals.[6] They thrive in aerobic conditions and the microaerophilic gut environment of animals. Rosculus can thrive in anaerobic culture. It is unknown if their preferred habitat is free-living or endozoic.[3]
Some host species can harbor different helkesid genera and species. One animal can be infected by multiple species simultaneously, and one species can also infect different animal hosts. More sampling of hosts, amoebae and molecular data is needed to better understand the life history and ecology of these protists.[3]
Evolution and systematics
editHistory
editHelkesida is a group initially named Sainouroidea. It was discovered in 2009 as a highly divergent clade within Cercozoa through phylogenetic analyses that used the sequencing of 18S ribosomal RNA from Cholamonas cytrodiopsidis, Sainouron acronematica and Helkesimastix marina. It is a molecularly diverse clade that branches within a group of ancestrally amoeboid bi-flagellates that usually lack an outer cell coat, known as Monadofilosa.[5] A 2016 study revealed a previously unknown wide diversity of Sainouroidea in fecal environments. Previous environmental samplings excluded sequences from Sainouroidea due to their highly divergent 18S rDNA sequences.[6] A 2018 study described several new genera and species.[3]
The initial name for this group, Sainouroidea, had the -oidea suffix for superfamilies, but it was not assigned to any existing classes or orders due to the uncertainty of its phylogenetic position.[5] In a 2018 revision, the class Helkesea and order Helkesida were created as a substitute for this name. Sainouroidea was then modified to only include one of the three helkesid families, Sainouridae. A second superfamily, Helkesimastigoidea, was created to host the remaining two families, Helkesimastigidae and Guttulinopsidae.[1]
Classification
edit| Phylogeny of Helkesida | ||||||||||||||||||||||||||||||||||||||||||||||||
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| Cladogram of Helkesida, based on a 18S rDNA phylogenetic analysis within a 2018 study.[3] The study names this group "Sainouroidea" due to being published prior to the taxonomic change to Helkesida.[1] |
Currently, Helkesida contains 24 species distributed in 9 genera, 3 families[2] and 2 superfamilies.[1] Additionally, many OTUs found through environmental sequencing may represent undescribed clades.[4][6]
- Superfamily Sainouroidea Cavalier-Smith et al. 2009 emend. 2018
- Family Sainouridae Cavalier-Smith 2008
- Acantholus Schuler & Brown 2018[3]
- Acantholus ambigus Schuler & Brown 2018
- Cholamonas Flavin, O'Kelly, Nerad & Wilkinson 2000[7]
- Homocognata Schuler, Silberman & Brown 2018[3]
- Homocognata vulgaris Schuler, Silberman & Brown 2018
- Sainouron Sandon 1924[8]
- Sainouron acronematica Cavalier-Smith et al. 2008[9]
- Sainouron mikroteron Sandon 1924
- Acantholus Schuler & Brown 2018[3]
- Family Sainouridae Cavalier-Smith 2008
- Superfamily Helkesimastigoidea Cavalier-Smith 2018
- Family Helkesimastigidae Cavalier-Smith 2008
- Helkesimastix Woodcock & Lapage 1915[10]
- Helkesimastix faecicola Woodcock & Lapage 1915
- Helkesimastix major Woodcock 1921
- Helkesimastix marina Cavalier-Smith 2009[5]
- Helkesimastix Woodcock & Lapage 1915[10]
- Family Guttulinopsidae Olive 1970
- Guttulinopsis Olive 1901[11]
- Guttulinopsis clavata Olive 1901
- Guttulinopsis erdosi Schuler, Silberman & Brown 2018
- Guttulinopsis rogosa Schuler, Tice, Silberman & Brown 2018
- Guttulinopsis stipitata Olive 1901
- Guttulinopsis vulgaris Olive 1901
- Olivorum Schuler, Tice, Silberman & Brown 2018[3]
- Olivorum cimiterus Schuler, Tice, Silberman & Brown 2018
- Puppisaman Schuler & Brown 2018[3]
- Puppisaman gallanis Schuler & Brown 2018
- Rosculus Hawes 1963[12]
- Rosculus hawesi Schuler, Tice & Brown 2018
- Rosculus incognitus Schuler & Brown 2018
- Rosculus ithacus Hawes 1963
- Rosculus liberus Schuler & Brown 2018
- Rosculus macrobrachii Aravindan, Kalavati & Sheeja 2002
- Rosculus philanguis Schuler, Silberman & Brown 2018
- Rosculus piscicus Schuler, Silberman & Brown 2018
- Rosculus terrestris Jousset, Bass & Geisen 2016
- Rosculus vulgaris Schuler, Silberman & Brown 2018
- Guttulinopsis Olive 1901[11]
- Family Helkesimastigidae Cavalier-Smith 2008
References
edit- ^ a b c d e f Thomas Cavalier-Smith; Ema E-Yung Chao; Rhodri Lewis (17 April 2018). "Multigene phylogeny and cell evolution of chromist infrakingdom Rhizaria: contrasting cel organisation of sister phyla Cercozoa and Retaria". Protoplasma. doi:10.1007/S00709-018-1241-1. ISSN 0033-183X. PMC 6133090. PMID 29666938. Wikidata Q53073157.
- ^ a b c Adl SM, Bass D, Lane CE, Lukeš J, Schoch CL, Smirnov A, Agatha S, Berney C, Brown MW, Burki F, Cárdenas P, Čepička I, Chistyakova L, del Campo J, Dunthorn M, Edvardsen B, Eglit Y, Guillou L, Hampl V, Heiss AA, Hoppenrath M, James TY, Karnkowska A, Karpov S, Kim E, Kolisko M, Kudryavtsev A, Lahr DJG, Lara E, Le Gall L, Lynn DH, Mann DG, Massana R, Mitchell EAD, Morrow C, Park JS, Pawlowski JW, Powell MJ, Richter DJ, Rueckert S, Shadwick L, Shimano S, Spiegel FW, Torruella G, Youssef N, Zlatogursky V, Zhang Q (2019). "Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes". Journal of Eukaryotic Microbiology. 66 (1): 4–119. doi:10.1111/jeu.12691. PMC 6492006. PMID 30257078.
- ^ a b c d e f g h i Schuler GA, Tice AK, Pearce RA, Foreman E, Stone J, Gammill S, Willson JD, Reading C, Silberman JD, Brown MW (2018). "Phylogeny and Classification of Novel Diversity in Sainouroidea (Cercozoa, Rhizaria) Sheds Light on a Highly Diverse and Divergent Clade" (PDF). Protist. 169 (6): 853–874. doi:10.1016/j.protis.2018.08.002. PMID 30415103. S2CID 53289638.
- ^ a b c Brown MW, Kolisko M, Silberman JD, Roger AJ (2012). "Aggregative Multicellularity Evolved Independently in the Eukaryotic Supergroup Rhizaria". Current Biology. 22 (12): 1123–1127. doi:10.1016/j.cub.2012.04.021. PMID 22608512. S2CID 17510471.
- ^ a b c d Cavalier-Smith T, Lewis R, Chao EE, Oates B, Bass D (2009). "Helkesimastix marina n. sp. (Cercozoa: Sainouroidea superfam. n.) a Gliding Zooflagellate of Novel Ultrastructure and Unusual Ciliary Behaviour". Protist. 160 (3): 452–479. doi:10.1016/j.protis.2009.03.003. PMID 19523874.
- ^ a b c Bass D, Silberman JD, Brown MW, Pearce RA, Tice AK, Jousset A, Geisen S, Hartikainen H (2016). "Coprophilic amoebae and flagellates, including Guttulinopsis, Rosculus and Helkesimastix, characterise a divergent and diverse rhizarian radiation and contribute to a large diversity of faecal-associated protists". Environ Microbiol. 18 (5): 1604–1619. doi:10.1111/1462-2920.13235. PMID 26914587.
- ^ Flavin M, O'Kelly CJ, Nerad TA, Wilkinson G (2000). "Cholamonas cyrtodiopsidis gen. n., sp. n.(Cercomonadida), an endocommensal, mycophagous heterotrophic flagellate with doubled kinetid". Acta Protozoologica. 39 (1): 51–60.
- ^ Sandon H (1924). "Some Protozoa from the Soils and Mosses of Spitsbergen. Results of the Oxford University Expedition to Spitsbergen, No. 27". Zoological Journal of the Linnean Society. 35 (237): 449–475. doi:10.1111/j.1096-3642.1924.tb00051.x.
- ^ Cavalier-Smith T, Lewis R, Chao EE, Oates B, Bass D (2008). "Morphology and Phylogeny of Sainouron acronematica sp. n. and the Ultrastructural Unity of Cercozoa". Protist. 159 (4): 591–620. doi:10.1016/j.protis.2008.04.002. PMID 18583188.
- ^ Woodcock HM, Lapage G (1915). "Observations on the life-cycle of a new flagellate, Helkesimastix fæcicola, n. g., n. sp.: Together remarks on the question of syngamy in the trypanosomes". Proc. R. Soc. Lond. B. 88 (604): 353–370. doi:10.1098/rspb.1915.0001.
- ^ Olive EW (1901). "A Preliminary Enumeration of the Sorophoreæ". Proceedings of the American Academy of Arts and Sciences. 37 (12): 333–344. doi:10.2307/20021671. JSTOR 20021671.
- ^ Hawes RS (1963). "On Rosculus ithacus gen. n., sp. n. (Protozoa, Amoebina), with special reference to its mitosis and phylogenetic relations". Journal of Morphology. 113 (2): 139–149. doi:10.1002/jmor.1051130202. PMID 14061990. S2CID 40212732.