DESCRIPTION OF THE PHYLUM KINETOPLASTEA (HONIBERG 1963)

EUKARYA> EXCAVATA> DISCICRISTATAE> KINETOPLASTA

Kinetoplasta (ki-ne-to-PLAS-ta) is made of two greek roots that mean movement (kines-e -κίνηση) and molded (plastos -πλαστοσ). The reference is to a specialized granular structure at the base of the flagellum called a kinetoplast, which is a modified mitochondrion.

INTRODUCTION TO THE KINETOPLASTA Taxa in this phylum are unicellular (Figures 1-3), and most have a single mitochondrion with a large amount of DNA (known as k-DNA; formerly it was called a kinetoplastid (text with tooltip) A kinetoplast is a modified mitochondrion that is associated with the basal body (kinetosome) of kinetoplastids. Their mitochondrion had a very large amount of DNA (called k-DNA) and stains almost as a second nucleus in the cell. ) associated with 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. . Though some taxa like Bodo (Figure 1) are free-living, this phylum is particularly notorious because of its parasitic taxa. Species of Trypanosoma (Figure 2) and Leishmania have been a scourge on humankind with lethal, debilitating, and disfiguring effects. Very likely, the chronic illness that Darwin suffered throughout his life after he returned from the voyage of the H.M.S. Beagle was a consequence of Chagas’ Disease caused by Trypanosoma cruzi, a disease of South America. This organism is transmitted by triatomid bugs (also called bed bugs) which usually acquire the parasites by taking a blood meal from an infected mammal like an armadillo, guinea pig, or dog. In the bug, the trypanosomes (see Figure 2) change into a form that resembles Euglena (called an epimastigote). The epimastigote can divide and then concentrate in the rectal area of the bug, and when the triatomid takes a blood meal, the bug defecates, which releases the epimastigotes near the wound. Those that get into the wound can enter the peripheral blood and infect certain cells where they lose their flagellum and divide in the amastigote stage. When the cell dies, they are released into the circulatory system where they change into the trypanosome stage. An infected person, if untreated, will have a chronic illness that can manifest itself as heart disease or disease of the bowels. The African counterpart is African Sleeping Sickness caused by another Trypanosoma species, T. brucei. In this case the protist is transmitted by Tse-tse flies in which it goes into the epimastigote stage and concentrates in the salivary glands of the fly. When the fly takes a blood meal, it injects the epimastigotes into the peripheral blood and the protist completes its life cycle very much like T. cruzi. However, sleeping sickness usually begins to affect the nervous system and the brain in which lesions develop, leading to death. The life cycles of T. cruzi and T. brucei are very similar and can be seen in the CDC illustration. Leishmania has a similar life cycle, but it usually remains in the amastigote stage when in the vertebrate host. All of the morphological changes that occur in the kinetoplastids do so in the absence of sexual reproduction. That is, they have a morphological life history, not a sexual life history. Margulis and Schwartz (1988 and 1998), Margulis et al. (1990), Sleigh et al. (1984), Lee and Hunter (1985), and Taylor (1976) consider the kinetoplastids to be a somewhat coherent group, unified by the presence of a modified mitochondrion called a kinetoplast. Margulis and Schwartz (1988) and Vickerman (1990b) consider this group to be a class with 2 suborders within a large, heterogeneous collection of flagellated organisms called the “Zoomastigina” (Pr-8). We have raised the classes of the kinetoplastids to the phylum level as have Sleigh et al. (1984). Consequently, we have raised the suborders of Vickerman (1990b) to class status. Taylor (1976) proposes a close association between the euglenophytes and the kinetoplastids. Similarly, Margulis and Schwartz (1998) group the amoeboflagellates, kinetoplastids, euglenoids, and Stephanopogon together in their phylum, Discomitochondria (Pr-12). The 16S-like rRNA analysis of Pace et al. (1986) shows that Trypanosoma is very different from the other eukaryotes studied [including Oxymonas, a member of the Margulis and Schwartz (1998) phylum, Archaeprotista Pr-1]. Patterson (1999) in his summary article unites them into a group with the euglenoids which we interpret as a kingdom. Likewise, Baldauf (2003) unites the euglenoids and kinetoplastids along with the amoeboflagellates and cellular slime molds into a clade called “Discicrtistae”. The treatment of Cavalier-Smith (2003a) is similar to that of Baldauf (2003a), but he adds the enigmatic Postgaardia (Figure 3) to the group. The system used below is a modification of Cavalier-Smith (2003a, see Figure 4), but we have raised his subphylum Saccostoma to phylum-level and called it Kinetoplastea.

FIGURE 1. Bodo, a small free-living kinetoplastid, showing both emergent flagella. Image from http://www.biol.tsukuba.ac.jp/~inouye/ino/e/bodo.gif	FIGURE 2. Trypanosoma, a blood parasite of vertebrates, uses blood-feeding insects as its intermediate hosts. Image from http://www.med.uni-marburg.de/stpg/ukm/lt/hygiene/schwarz/projects.html	FIGURE 3. Illustration of Postgaardia, an unusual free-living unicell, which has a mitochondrion without cristae. The outside of the cell is covered with bacteria which may aid in respiration. Image from http://microscope.mbl.edu/baypaul/microscope/thebiologyof/euglenozoa/eugzoahtmls/eugzoa_postgard.htm

FIGURE 4. Cladogram that shows the relationships between taxa of the Kinetoplastea (taxa in shaded box) according to Cavalier-Smith (2003). The topology of the cladogram follows the analyses of Von der Heyden et al. (2004) and Marin et al. (2003). EZ = Euglenozoa clade.

LITERATURE CITED Baldauf, S. L. 2003a. The deep roots of eukaryotes. Science. 300 (5626): 1701-1703. Cavalier-Smith, T. 2003a. Protist phylogeny and the high-level classification of Protozoa. European Journal of Protistology. 39:338-348. Lee, J. J. and S.H. Hunter. 1985. Kinetoplastida. In: Lee, J.J., S.H. Hunter, and E.C. Bovee, eds. An Illustrated Guide to the Protozoa. Allen Press. Lawrence, Kansas. pp. 141-155. 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. Pace, N.R., G.J. Olsen,and C.R. Woese. 1986. Ribosomal RNA phylogeny and the primary lines of evolutionary descent. Cell.45: 325-326. Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist. 154 (Suppl.): S96–S124. 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. Vickerman, K. 1990b. Kinetoplastida. 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. 218-238.

By Jack R. Holt. Last revised: 02/17/2015