Trichomonadea and Hypermastigea phylum Trichozoa

The trichomonads and hypermastigotes belong to the parabasalian protozoa, which are primarily endozoic symbionts or parasites. About half of the genera occur in wood-eating insects, such as the roach Crypotcercus, but two free-living species are known from water solutions rich in dissolved organic matter. Their internal structure has an elaborate fibrous cytoskeleton supporting the basal bodies, the nucleus and the anterior of the cell. They are amitochondriate anaerobes that feed by amoeboid phagocytosis on microdetritus in the digestive tract of host organisms. Their metabolism is enhanced by hydrogenosomes which carry out respiration of pyruvate to acetyl-Co A, CO2 and H2, producing ATE The storage material is glycogen. Mitosis is closed, with the chromosomes attached to the nuclear membrane, and an extranuclear spindle. The Earabasala derive their name from an elaborate system of fibrous cytoskeleton, that emanates from basal bodies to support the nucleus and the anterior of the cell, and hold in place long Golgi bodies adjacent to the basal bodies. These species are therefore capable of extensive protein synthesis and secretion through the endomembrane network. Many parabasalian species, particularly the Hypermastigea, are important to decomposition for their role in the digestion of wood microdetritus in the digestive tract of wood-eating cockroaches and the lower termites. Different species of Trichozoa are found in different populations and species of wood-eating insects.

The basic structure of a Trichozoa can be described from a typical Trichomonadea such as Trichomonas (Fig. 1.4). There are four basal bodies, with one trailing and three anterior cilia. The recurrent cilium is intracellular and held by an extension of the cell membrane (it appears

Fig. 1.4. The Trichozoa Trichmonas, showing a recurrent cilium (CR) held by a membranelle, an axostyle (Ax), pelta (P), anterior nucleus (N) and three anterior cilia. Scale bar 10 ^m.

as an undulating membrane). The costa is a contractile rod supporting the trailing cilium. It extends from the basal body and contributes to motility. The anterior of the cell is reinforced by a pelta, and an axostyle wraps at least partially around the nucleus and extends the length of the cell. It appears as a central cone that extends out of the cell in some species. A fibrous rootlet (rhizoplast) from a basal body extends to the nucleus. From the anterior-most basal body, cytoskeletal elements (the parabasal fibres) extend to the nucleus and support two elongated Golgi bodies. There is no cytostome and no supporting microtubules under the cell membrane. The cell is therefore very flexible, and phagocytosis occurs along the cell membrane, ingesting bacteria and larger microde-tritus. Most species of trichomonads are 5-25 ^m intestinal parasites in animals. Some such as Dientamoeba and Histomonas do not have emerging cilia and are amoeboid. Others are symbionts in termites, such as Mixotricha paradoxa.

The Hypermastigea are larger cells, of approximately 100 ^m, that resemble Trichomonas or Monocercomonas but with the cytoskeletal structures replicated many times across the cell, i.e. there are multiple pairs of basal bodies at the anterior with cilia spiralling along the body towards the posterior, or emerging as tufts at the anterior. The axostyle and other cytoskeletal elements from the basal bodies merge into a single large unit with complex modifications. Typical genera are Barbulanympha, Joenia, Lophomonas and Spirotrichonympha (Fig. 1.5). The Polymonadea are similar to other hypermastigote Parabasala, but with multiple nuclei, axostyle and parabasal bodies. They resemble hyper-mastigotes without the merged organelles (e.g. Calonympha, Coronympha and Snyderella). Species of hypermastigotes are found exclusively in

Fig. 1.5. The hypermastigote Barbulanympha with many axostyles, extensive anterior cytoskeleton and numerous anterior cilia. Cilia (C), parabasal bodies (PB), nucleus (N), axostyle (Ax), food vacuoles (FV). Scale bar 25 ^m.

wood-eating cockroaches and lower termites, where sometimes they are accommodated in specialized termite gut chambers. As with other termite symbionts, they are associated with extracellular surface spirochetes (bacteria) which contribute to motility, as well as intracellular symbiotic bacteria. These species cooperate together in the digestion of woody microdetritus ingested by the insect.

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