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Trimastix Kent 1880

Alastair Simpson and Vladimir Hampl
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Containing group: Preaxostyla

Introduction

Trimastix is a group of free-living heterotrophic flagellates.  There are only a tiny handful of species, and their ecological role is essentially unstudied.  Trimastix however is in an interesting evolutionary position as the sister group to oxymonads, a moderately diverse and well-known group of animal commensals/symbionts (see Dacks et al., 2001; Hampl et al., 2009).  Like oxymonads they are anaerobes/microaerophiles that lack classical mitochondria, and much of the current interest in Trimastix concerns the evolution of mitochondrial organelles in anaerobic eukaryotes (see Hampl et al., 2008).

Characteristics

General appearance, and apomorphies

Trimastix cells are roughly pyriform (teardrop-shaped), and about 10-25 micrometres long, depending on the species (Kent, 1880-2, Klebs, 1893, Bernard et al., 2000; See title illustrations and Fig. 1).  Cells are usually observed swimming freely, not attached to a surface.  The flagella insert near the anterior end of the cell.  Despite the name, Trimastix cells have four flagella, not three.  One flagellum is directed posteriorly, another anteriorly (more or less), and two others are directed laterally – one left and one right (Last title illustration, and Fig. 1b).  As a consequence it is difficult to see all four flagella at the same time, and when the genus was first described by Kent (1880-2) one flagellum was overlooked.  

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Figure 1. Light microscopy (DIC) images of Trimastix pyriformis (A,B) and Trimastix marina (C,D). ©

The posterior flagellum bears two very broad vanes with thickened margins, which can be seen most clearly by electron microscopy (Fig. 2, 3b), but can also sometimes be distinguished by light microscopy as well (Brugerolle and Patterson, 1997; O’Kelly et al., 1999; Simpson et al., 2000).  In one species, Trimastix marina, the anterior flagellum is thickened as well (Simpson et al., 2000; see Fig. 1c, 2, 3a).

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Figure 2. Trimastix marina. Transmission electron micrograph showing transverse section of all four flagella from one cell. Note the broad vanes on the posterior flagellum, with thickened margins, and the thickening of the anterior flagellum © Alastair Simpson

As with many other excavates (see jakobids, for example), one side of the cell is shaped in the form of a broad groove, which is used as a feeding device (See Title illustrations, Fig. 1c, 3a, 3b).  Suspended particles such as bacteria are moved into the feeding groove in a current generated by the beating action of the posterior flagellum.  In Trimastix there is a discrete pocket-like structure which is directed laterally from the posterior end of the groove (Fig. 3a).  This functions as a cytostome – it is the site where food particles are phagocytosed (Brugerolle and Patterson, 1997; Simpson et al., 2000).  Though small it is descernable by light microscopy (Fig. 1a, 1c, 1d).  The cytoskeleton supporting the groove is similar to that of other excavate taxa (see jakobids), though with some differences in detail (O’Kelly et al., 1999; Simpson et al., 2000).
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Figure 3. Trimastix marina, Scanning Electron Micrographs. A. Whole cell portrait, highlighting the ventral feeding groove.  The very posterior end of the groove, deflected laterally is the opening of the cytostome - the site of ingestion.  B. Mid-portion of the groove and the broad vanes on the posterior flagellum . ©

Simpson et al. (2000) identified the following as distinct features of Trimastix spp., when compared to other excavate taxa, and these represent possible apomorphies.  They are all features of the cytoskeleton that may only be observed by electron microscopy:

Mitochondrial organelles

In place of classical mitochondria Trimastix spp. have organelles that are bounded by two membranes, but that lack mitochondrial cristae (Brugerolle and Patterson, 1997; O’Kelly et al., 1999; Simpson et al., 2000).  The organelles of Trimastix also tend to be smaller than typical mitochondria, especially in Trimastix marina (Brugerolle and Patterson, 1997; O’Kelly et al., 1999; Simpson et al., 2000).  Nuclear transcripts from Trimastix pyriformis include a dozen ‘mitochondrial proteins’ that are normally involved in protein import and folding, or metabolic functions (Hampl et al., 2008). This indicates that these organelles share an evolutionary history with typical mitochondria (Hampl et al., 2008).  These mitochondrial proteins include all the major proteins of the glycine cleavage system, a mitochondrial pathway which is not present in toto in the mitochondrion-like organelles of well studied anaerobic eukaryotes such as Giardia, Trichomonas and Entamoeba,  It is suspected that the mitochondrion-like organelles of Trimastix might function as hydrogenosomes (as in parabasalids), but this has not been demonstrated – although Trimastix does produce transcripts for signature hydrogenosomal enzymes (hydrogenase, pyruvate:ferredoxin oxidoreductase), it is not known whether these enzymes are active in the mitochondrial organelle (Hampl et al., 2008).

Interestingly, the Trimastix [FeFe] hydrogenase is the same bacterial-like version of the enzyme found in Entamoeba, an organism that is not at all closely related to Trimastix (Hampl et al., 2008).  This enzyme was likely acquired by lateral gene transfer into an ancestor of Trimastix, or perhaps all Preaxostyla.

Discussion of Phylogenetic Relationships

There are only three recognized species of TrimastixTrimastix marina, Trimastix pyriformis, and Trimastix inequalisTrimastix convexa Grasse is regarded as a junior synonym of Trimastix pyriformis Klebs (see Bernard et al., 2000).  Molecular phylogenies consistently group Trimastix marina and Trimastix pyriformis as a clade (Dacks et al., 2001; Simpson et al., 2006), supporting the monophyly of Trimastix, but there are no molecular data for Trimastix inequalis with which to test the internal phylogenetic relationships.

Other Names for Trimastix Kent 1880

References

Bernard, C., Simpson, A.G.B. and Patterson, D.J. (2000) Some free-living flagellates (Protista) from anoxic habitats. Ophelia 52: 113-142.

Brugerolle, G and Patterson, D.J. (1997) Ultrastructure of Trimastix convexa Hollande, an amitochondriate anaerobic flagellate with a previously undescribed organization. Europ. J. Protistol. 33: 121-130.

Dacks, J.B., Silberman, J.D., Simpson, A.G.B., Moriya, S., Kudo, T., Ohkuma, M. and Redfield, R.J. (2001) Oxymonads are closely related to the excavate taxon Trimastix. Mol Biol Evol, 18, 1034-1044.

Hampl, V., Hug, L., Leigh, J.W., Dacks, J.B., Lang, B.F., Simpson, A.G.B. and Roger, A.J. (2009) Phylogenomic analyses support the monophyly of Excavata and resolve relationships among eukaryotic "supergroups". Proc Natl Acad Sci U S A, 106, 3859-3864.

Hampl, V., Silberman, J.D., Stechmann, A., Diaz-Trivino, S., Johnson, P.J. and Roger, A.J. (2008) Genetic evidence for a mitochondriate ancestry in the 'amitochondriate' flagellate Trimastix pyriformis. PLoS One, 3, e1383.

Kent, W.S. (1880-1882). A manual of the Infusoria. (3 vols) London.

Klebs, G., (1893) Über die Organisation einiger Flagellatengruppen und ihre Beziehungen zu anderen Infusorien. - Unters. Bot. Inst. Tübingen. 1: 233-262.

O'Kelly C.J., Farmer M.A. and Nerad T.A. (1999) Ultrastructure of Trimastix pyriformis (Klebs) and similarities of Trimastix species with retortamonads and jakobids. Protist 150, 149-162.

Simpson, A.G.B., Bernard, C. and Patterson, D.J. (2000) The ultrastructure of Trimastix marina Kent, 1880 (Eukaryota), an excavate flagellate. Europ. J. Protistol. 36, 229-252.

Simpson, A.G.B., Inagaki, Y. and Roger, A.J., (2006) Comprehensive multigene phylogenies of excavate protists reveal the evolutionary positions of “primitive” eukaryotes. Mol. Biol. Evol. 23: 615-625.

Information on the Internet

Title Illustrations
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Scientific Name Trimastix marina
Comments Monoprotistan culture, strain WL
Specimen Condition Live Specimen
Identified By Alastair Simpson
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2009 Alastair Simpson
Scientific Name Trimastix marina
Comments Scanning electron micrograph of Trimastix marina trophozoite
Specimen Condition Dead Specimen
Life Cycle Stage Trophozoite
Copyright ©
Scientific Name Trimastix pyriformis
Comments From monoprotiston culture, strain RCP / RCP-MX
Specimen Condition Live Specimen
Identified By Alastair Simpson
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2009 Alastair Simpson
Scientific Name Trimastix pyriformis
Comments From monoprotistan culture, strain RCP / RCP-MX
Specimen Condition Live Specimen
Identified By Alastair Simpson
Image Use creative commons This media file is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0.
Copyright © 2009 Alastair Simpson
About This Page

This page is being developed as part of the Tree of Life Web Project Protist Diversity Workshop, co-sponsored by the Canadian Institute for Advanced Research (CIFAR) program in Integrated Microbial Biodiversity and the Tula Foundation.

Alastair Simpson
Dalhousie University, Halifax, Nova Scotia, Canada


Dalhousie University, Halifax, Nova Scotia, Canada

Correspondence regarding this page should be directed to Alastair Simpson at and Vladimir Hampl at

Page: Tree of Life Trimastix Kent 1880. Authored by Alastair Simpson and Vladimir Hampl. The TEXT of this page is licensed under the Creative Commons Attribution-NonCommercial License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

Citing this page:

Simpson, Alastair and Vladimir Hampl. 2009. Trimastix Kent 1880. Version 16 November 2009. http://tolweb.org/Trimastix/97437/2009.11.16 in The Tree of Life Web Project, http://tolweb.org/

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