Heterolobosea

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Heterolobosea
Naegleria (formes) en.png
The three different stages of N. fowleri
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Discoba
Clade: Discicristata
Phylum: Heterolobosea
Page & Blanton, 1985 [1]
Classes
Diversity
~170 species [1]
Synonyms
  • Percolozoa Cavalier-Smith, 1991
  • Acrasiomycota Whittaker 1969
  • Amoeboflagellates
  • Pseudociliata Cavalier-Smith 1993
  • Schizopyrenia
  • Tetramitozoa Dillon 1963
  • Stephanopogonophyta Doweld 2001
  • Stephanopogonomorpha Sleigh et al. 1984

Heterolobosea or Percolozoa, commonly known as amoebomastigotes, [2] is a phylum of protists including many amoeboflagellates. Naegleria fowleri , the causative agent of the often fatal disease amoebic meningitis, is the only member of this phylum infectious to humans. Typically, their life cycle alternates between flagellate and amoeboid stages.

Contents

Characteristics

Cellular features of the amoeboid stage 2023 Heterolobosean-cropped.svg
Cellular features of the amoeboid stage

Most Percolozoa are found as bacterivores in soil, fresh water and occasionally in the ocean. [3] The only member of this group that is infectious to humans is Naegleria fowleri , the causative agent of the often fatal disease amoebic meningitis. [4] The group is closely related to the Euglenozoa, and share with them the unusual characteristic of having mitochondria with discoid cristae. [5] The presence of a ventral feeding groove in the flagellate stage, as well as other features, suggests that they are part of the Excavata group. [6]

The amoeboid stage is roughly cylindrical, typically around 20–40 μm in length. They are traditionally considered lobose amoebae, but are not related to the others, and unlike them, do not form true lobose pseudopods. Instead, they advance by eruptive waves, where hemispherical bulges appear from the front margin of the cell, which is clear. The flagellate stage is slightly smaller, with two or four anterior flagella anterior to the feeding groove. [4]

Usually, the amoeboid form is taken when food is plentiful, and the flagellate form is used for rapid locomotion. However, not all members are able to assume both forms. The genera Percolomonas , Lyromonas , and Psalteriomonas are known only as flagellates, while Vahlkampfia , Pseudovahlkampfia , and most acrasids do not have flagellate stages. As mentioned above, under unfavourable conditions, the acrasids aggregate to form sporangia. These are superficially similar to the sporangia of the dictyostelids, but the amoebae only aggregate as individuals or in small groups and do not die to form the stalk. [4]

Phylogeny

The first broadly sampled comprehensive phylogenomic (phylotranscriptomic) analysis of the group (from 2025) confirmed the monophyly of Heterolobosea and provided a robustly supported backbone of the phylogeny resulting in the revision of the classification of Heterolobosea to the family level. [1]

The basal split of the cladogram has been confirmed between the subphyla Pharyngomonada (monotypic, with a sole family Pharyngomonadidae) and Tetramitia. In Tetramitia, two main clades (new classes) were identified: Selenaionea, consisting of two orders Neovahlkampfiida and Selenaionida in previously unsuspected but fully supported sister relationship, and Eutetramitea, consisting of orders Creneida, Lyromonadida, Naegleriida (new, including acrasid slime molds), Percolomonadida and Pseudociliatida (represented by the single genus Stephanopogon ; not included in the new analysis but analyses based on 18S rRNA gene sequences have repeatedly shown its close relationship to Percolomonadida with high statistical support): [1]

Heterolobosea

Taxonomy

These are collectively referred to as schizopyrenids, amoeboflagellates, or vahlkampfids. They also include the acrasids, a group of social amoebae that aggregate to form sporangia. The entire group is usually called the Heterolobosea, but this may be restricted to members with amoeboid stages.

One Heterolobosea classification system is: [7]

Pleurostomum flabellatum has recently been added to Heterolobosea. [8]

Phylum Percolozoa Cavalier-Smith 1991 [9]

History

The Heterolobosea were first defined by Page and Blanton in 1985 [11] as a class of amoebae, and so only included those forms with amoeboid stages. Cavalier-Smith created the phylum Percolozoa for the extended group, together with the enigmatic flagellate Stephanopogon . [12]

Cavalier-Smith maintained the Heterolobosea as a class for amoeboid forms. He has defined Percolozoa as "Heterolobosea plus Percolatea classis nov." [5]

References

  1. 1 2 3 4 Pánek, Tomáš; Tice, Alexander K.; Corre, Pia; Hrubá, Pavla; Žihala, David; Kamikawa, Ryoma; Yazaki, Euki; Shiratori, Takashi; Kume, Keitaro; Hashimoto, Tetsuo; Ishida, Ken-ichiro; Hradilová, Miluše; Silberman, Jeffrey D.; Roger, Andrew; Inagaki, Yuji; Eliáš, Marek; Brown, Matthew W.; Čepička, Ivan (16 January 2025). "An expanded phylogenomic analysis of Heterolobosea reveals the deep relationships, non-canonical genetic codes, and cryptic flagellate stages in the group". Molecular Phylogenetics and Evolution. 204. Academic Press in Elsevier: 108289. Bibcode:2025MolPE.20408289P. doi:10.1016/j.ympev.2025.108289. ISSN   1095-9513. PMID   39826589.{{cite journal}}: CS1 maint: article number as page number (link)
  2. ↑ Margulis, Lynn; Chapman, Michael J. (2009). Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth (4th corrected ed.). London: Academic Press. ISBN   9780123736215.
  3. ↑ Esteban, Genoveva F.; Finlay, Bland J.; Warren, Alan (2015), "Free-Living Protozoa" , Thorp and Covich's Freshwater Invertebrates, Elsevier, p. 122, doi:10.1016/b978-0-12-385026-3.00007-3, ISBN   978-0-12-385026-3 , retrieved 2024-12-14
  4. 1 2 3 Pánek, Tomáš; Simpson, Alastair G. B.; Brown, Matthew W.; Dexter Dyer, Betsey (2016), Archibald, John M.; Simpson, Alastair G.B.; Slamovits, Claudio H.; Margulis, Lynn (eds.), "Heterolobosea" , Handbook of the Protists, Cham: Springer International Publishing, pp. 1–42, doi:10.1007/978-3-319-32669-6_10-1, ISBN   978-3-319-32669-6 , retrieved 2024-12-14
  5. 1 2 Cavalier-Smith T (November 2003). "The excavate protozoan phyla Metamonada Grassé emend. (Anaeromonadea, Parabasalia, Carpediemonas, Eopharyngia) and Loukozoa emend. (Jakobea, Malawimonas): their evolutionary affinities and new higher taxa". Int. J. Syst. Evol. Microbiol. 53 (Pt 6): 1741–58. doi: 10.1099/ijs.0.02548-0 . PMID   14657102.
  6. ↑
  7. ↑ "Heterolobosea" . Retrieved 2009-03-25.
  8. ↑ Park JS, Simpson AG, Lee WJ, Cho BC (July 2007). "Ultrastructure and phylogenetic placement within Heterolobosea of the previously unclassified, extremely halophilic heterotrophic flagellate Pleurostomum flabellatum (Ruinen 1938)". Protist. 158 (3): 397–413. doi:10.1016/j.protis.2007.03.004. PMID   17576098.
  9. ↑ "Part 1- Virae, Prokarya, Protists, Fungi". Collection of genus-group names in a systematic arrangement. Archived from the original on 14 August 2016. Retrieved 30 June 2016.
  10. 1 2 Hohlfeld, Manon; Meyer, Claudia; Schoenle, Alexandra; Nitsche, Frank; Arndt, Hartmut (January 2023). "Biogeography, autecology, and phylogeny of Percolomonads based on newly described species". Journal of Eukaryotic Microbiology. 70 (1): e12930. doi: 10.1111/jeu.12930 . PMID   35712988.{{cite journal}}: CS1 maint: article number as page number (link)
  11. ↑ Page, F.C.; R.L. Blanton (1985). "The Heterolobosea (Sarcodina: Rhizopoda), a new class uniting the Schizopyrenida and Acrasidae (Acrasida)". Protistologica. 21: 121–132.
  12. ↑ Cavalier-Smith, T. (1991). "Cell diversification in heterotrophic flagellates". In D.J. Patterson & J. Larsen (ed.). The Biology of Free-living Heterotrophic Flagellates. Oxford University Press. pp. 113–131. ISBN   9780198577478.
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