DESCRIPTION OF THE PHYLUM PARABASALA (HONIGBERG 1973)

EUKARYA> EXCAVATA> EUEXCAVATAE> PARABASALA

Parabasala (pa-ra-BA-sa-la) comes from two Greek roots that mean beside (para -παρα) and base (bas-e -βάση). The reference is to a specialized organelle that is intimately associated with the basal bodies in this phylum.

INTRODUCTION TO THE PARABASALA The parabasalids are large multiflagellated unicells that inhabit the guts of insects. They seem to be united by the synapomorphy of a large modified golgi (text with tooltip) Golgi apparatus (also called dictyosome) is an internal membrane system of stacked flattened sacs. They occur in nearly all eukaryotes and are involved in storing and secreting cellular products. called a parabasal body (text with tooltip) Parabasal bodies are large modified golgi bodies that lie in association with the basal bodies and flagellar roots of the Parabasalotista. , a structure that gives the group its name. Some taxa are associated with mammals and birds. Trichomonas vaginalis is an agent of human disease. Others are important as commensals that allow termites and wood-eating cockroaches to digest the cellulose of wood. The flagella seem to be in clusters of 4, often with 3 anterior (text with tooltip) An anteriorly-directed flagellum extends in the direction of the motion of the motile cell. The interpretation is that the flagellum functions by pulling the cell. and one posterior ( recurrent (text with tooltip) Recurrent flagella bend to the posterior end of the cell. Typically, they are identified as recurrent when anteriorly-directed flagella are present. ) flagellum. At least some of the basal bodies (text with tooltip) Basal bodies (also called kinetosomes) are organelles that are not membrane-bound. All eukaryotic flagella (also called undulipodia) are underlain or attached to the cell by the basal body. The basal body is a microtubular structure with the general formula 9(3)+0. They are indistinguishable from centrioles. are associated with parabasal (text with tooltip) Parabasal bodies are large modified golgi bodies that lie in association with the basal bodies and flagellar roots of the Parabasalotista. structures composed of striated filamentous fibers with closely allied golgi complexes. The striated or parabasal root very often is associated with a nucleus (e.g. Trichomonas, Figure 1). Some taxa are multinucleate and the flagella-nuclear units, called karyomastigonts are numerous (as in Spirotrichonympha, Figure 2), or many sets of flagella whose roots encapsulate a large nucleus (Lophomonas, Figure 3). Often the flagellar roots extend through the cell as an axostyle (Figures 1 and 3), which holds the cell rigidly, despite it having a somewhat naked cell covering. They have specialized cytostomes through which they take in food items (see the cytostome of Trychonympha, Figure 4). During mitosis, the nuclear membrane remains intact ( closed (text with tooltip) Mitosis is closed when the segregation of daughter chromosomes occurs within the bounds of the nuclear membrane (the nuclear membrane does not break down). ). The spindle is extranuclear (text with tooltip) Extra-nuclear spindles elaborate outside of a nucleus whose membrane does not break down. The spindle fibers attach to the nuclear envelope and, presumably, to a chromosome attached to the envelope. and extends across one side of the nucleus with chromosomes connected to microtubules at kinetochores (text with tooltip) A kinetochore is also called a centromere, the point on a chromosome to which the spindle fibers attach. situated in the nuclear envelope. The spindle poles are associated with “atractophores” (fibrous extensions from certain basal bodies). Meiosis (and therefore sexual reproduction) have never been observed. Margulis and Schwartz (1988) and Sleigh et al. (1984) considered the parabasalids to be a somewhat coherent group, unified by the presence of a modified golgi body called a parabasal body. Grell (1973) and Lee et al. (1985) lumped these organisms together with the metamonads (and other flagellated unicells). Likewise, Margulis and Schwartz (1988) and Margulis et al. (1990) treated this group as part of a large, heterogeneous collection of flagellated organisms called the “Zoomastigina” (Pr-8). Later, Margulis and Schwartz (1998) grouped these with other amitochondriates in a phylum called Archaeprotista (Pr-1), greatly divergent in form and presumably primitive in the eukaryotic tree. Earlier, Sleigh et al. (1984) raised the classes of the “Zoomastigina” to the phylum level in recognition of their disparity in structure. Prior to that, Taylor (1976) suggested that the Hypermastigid-Trichomonad-Diplomonad-Retortamonad complex was not primitive and had affinities with the chrysophytes. More recently, Taylor (1999) and Tudge (2000) by using both molecular and ultrastructural evidences supported the assumption that these were primitive taxa and a natural grouping. Thus their chaotic history seemed to be resolved by the Roger (1999) modification of the Archezoa Hypothesis. Then, revelations since 2000 (summarized in Cavalier-Smith 2003b) showed that the excavates were not primitive, and their apparent primitive state was due to the loss of mitochondria and an artifact of phylogenies based on single gene sequences. Baldauf (2003a) presents a consensus view based on molecular and ultrastructural characters in which this group is no longer considered primitive. In this system, the parabasalids are considered part of a natural group called the excavates which includes the diplomonads, retortomonads, and oxymonads. Figure 5 illustrates the two major clades of the Euexcavatae, in which the Parabasala occur in the symbiotic taxa clade together with Eopharyngia and Metamonadea.

FIGURE 1. Trichomonas cells stained to show nuclei. Recurrent flagellum forms an undulating membrane (text with tooltip) An undulating membrane is an upraised portion of the cell membrane that is underlain by a flagellum to form a waving fin-like structure. which is evident on the lower cell. Image from http://www.medicine.mcgill.ca/tropmed/	FIGURE 2. A DIC micrograph of Spirotrichonympha showing the spiral of karyomastigonts (text with tooltip) A karyomastigont is a 'unit' that includes basal bodies, flagellar roots, and a nucleus. down the cell. Image from http://microscope.mbl.edu/	FIGURE 3. A drawing of Lophomonas to show the nucleus encapsulated by flagellar roots (text with tooltip) Flagellar roots are microtubular structures that arise from the basal bodies and elaborate to the inside of the cell. They may connect to the nucleus (as part of a karyomastigont) or course their way into the cell such that they form other structures like axostyles. , which then form an elongate axostyle (text with tooltip) An axostyle is rod-like microtubular structure that occurs in certain Metamonadotista and Parabasalotista. The axostyle runs through the axis of the cell from the anterior (usually anchored around the nucleus) to the posterior end, often forming an extended point at the posterior end. . Image from http://microscope.mbl.edu/	FIGURE 4. A DIC micrograph of Trichonympha. Note the tube-like cytostome extending from the top of the cell. Image from the Systematics Biodiversity Image Archive

FIGURE 5. A cladogram showing the relationships between the phyla of the Euexcavatae (taxa in bold). The parabasalids (in the shaded box) are part of the symbiotic clade. The relationships given here have been inferred from Lara et al. (2006), Kolisko et al. (2008), and Malik et al. (2011).

LITERATURE CITED Baldauf, S. L. 2003a. The deep roots of eukaryotes. Science. 300 (5626): 1701-1703. Brugerolle, G., and J. P. Mignot. 1990. Retortamonadida. In: Margulis, L., J. O. Corliss, M. Melkonian, and D. J. Chapman, eds. 1990. Handbook of the Protoctista; the Structure, Cultivation, Habits and Life Histories of the Eukaryotic Microorganisms and Their Descendants Exclusive of Animals, Plants and Fungi. Jones and Bartlett Publishers. Boston. pp. 259-265. Cavalier-Smith, T. 2003a. Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology. 39:338-348. Cavalier-Smith, T. 2003b. The excavate protozoan phyla Metamonada Grasse emend. (Anaeromonadea, Parabasalia, Carpediemonas, Eopharyngia) and Loukozoa emend. (Jakobea, Malawimonas): their evolutionary affinities and new higher taxa. International Journal of Systematic and Evolutionary Microbiology. 53:1741-1758. Dyer, B. D. 1990c. Parabasalia. In: Margulis, L., J. O. Corliss, M. Melkonian, and D. J. Chapman, eds. 1990. Handbook of the Protoctista; the Structure, Cultivation, Habits and Life Histories of the Eukaryotic Microorganisms and Their Descendants Exclusive of Animals, Plants and Fungi. Jones and Bartlett Publishers. Boston . pp. 252-258. Grell, K. G. 1973. Protozoology. Springer-Verlag. New York. Honigberg, B. M. 1973. Remarks upon trichomonad affinities of certain parasitic protozoa. In Progress in Protozoology: Abstracts of Papers Read at the 4th International Congress of Protozoology, Clermont-Ferrand, 2–10 September 1973, p. 187. Edited by P. De Puytorac & J. Grain. Clermont-Ferrand: Universite´ de Clermont. Kolisko, M., I. Cepicka, V. Hampl, J. Leigh, A. J. Roger, J. Kulda, A. G. B. Simpson, and J. Flegr. 2008. Molecular phylogeny of diplomonads and enteromonads based on SSU rRNA, alpha-tubulin and HSP990 genes: implications for the evolutionary history of the double karyomastigont of diplomonads. BMC Evolutionary Biology. 8: 205 doi: 10.1186/1471-2148-8-205 Kudo, R.R. 1966. Protozoology. 5th ed. Charles C. Thomas Publisher. Springfield. Lara, E., A. Chatzinotas, and A. G. B. Simpson. 2006. Andalucia (n. gen.) – the deepest branch within jacobids (Jacobida: Excavata), based on morphological and molecular study of a new flagellate from soil. Journal of Eukayotic Microbiology. (53(2): 112-120. Lee, J. J. 1985. Order Retortamonadida. In: Lee, J.J., S.H. Hunter, and E.C. Bovee, eds. An Illustrated Guide to the Protozoa. Allen Press. Lawrence , Kansas. pp. 118-119. Malik, S-B., C. D. Brochu, I. Bilic, J. Yuan, M. Hess, J. M. Logsdon, and J. M. Carlton. 2011. Phylogeny of parasitic Parabasalia and free-living relatives inferred from conventional markers vs. Rpb1, a single-copy gene. PLoS ONE. 6(6): e20774. doi:10.1371/journal.pone.0020774 Margulis, L. and K. Schwartz. 1988. Five kingdoms, an illustrated guide to the phyla of life on earth. 2nd Edition. W.H. Freeman and Co. New York. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York. Margulis, L., J. O. Corliss, M. Melkonian, and D. J. Chapman, eds. 1990. Handbook of the Protoctista; the structure, cultivation, habits and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. Jones and Bartlett Publishers. Boston. Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist. 154 (Suppl.): S96–S124., Simpson, A. G. B. 2003. Cytoskeletal organization, phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota). International Journal of Systematic and Evolutionary Microbiology. 53: 1759-1777. Sleigh, M.A., J.D. Dodge and D.J. Patterson. 1984. Kingdom Protista. In: Barnes, R.K.S., ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc. Sunderland, Mass. Taylor, F.J.R. 1976. Flagellate Phylogeny: A Study in Conflicts. J. Protozool. 23: 28-40. [C,L] Taylor, F. J. R. 1999. Ultrastructure as a control for protistan molecular phylogeny. The American Naturalist. 154(supplement): S125-S136. Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York. [C,L] Vickerman, K. 1990a. Diplomonadida. In: Margulis, L., J. O. Corliss, M. Melkonian, and D. J. Chapman, eds. 1990. Handbook of the Protoctista; the structure, cultivation, habits and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. Jones and Bartlett Publishers. Boston. pp. 200-210.

By Jack R. Holt. Last revised: 02/17/2014