The class includes many human parasitic species that cause Chagas disease, leishmaniasis, and African sleeping sickness, others that are animal blood trypanosomes, fish tissue parasites and the Phytomonas which are parasites in plant latex vessels. The kinetoplastid name comes from a large clump of mitochondrial DNA, the kinetoplast, located anteriorly near the basal bodies. The kinetoplast DNA consists mostly of DNA minicircles (0.2-0.8 ^m long) or longer circles more typical of mitochondrial DNA (8-11 ^m). There are about 600 species of kinetoplastids. Most are parasitic such as the Trypanosoma and Leishmania, or commensal and parasitic bodonids, but many are free-living Bodonea found in soil and freshwater habitats. These bodonids are small species (3-15 ^m) with two heterodynamic anterior cilia emerging from an invagination (e.g. Bodo, Dimastigella and Rhynchomonas) (Fig. 1.8). Both cilia have a supporting proteinaceous rod that extends to the basal bodies. Supporting cytoskeletal elements extend from the basal bodies as ventral and dorsal fibres, along the length of the cell. The cell membrane is supported by a layer of longitudinal microtubules. A cytostome region, usually a well-developed invagination, is reinforced on one side with microtubules from the basal bodies. Certain genera, such as Bodo, have non-tubular mastigonemes in tufts on the anterior cilium. Cells have a contractile
Fig. 1.8. Rhynchomonas, a free-living bodonid. Scale bar 5 ^m.
vacuole which empties into the invagination that holds the cilia, a Golgi-dictyosome and a single mitochondrion with flat cristae constricted at the base. Mitosis is closed, with an internal spindle, and sexual stages are not known for free-living bodonids. Soil species are bacterivorous by phagocytosis at the cytostome, but osmotrophy should not be excluded.
Was this article helpful?