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A Microbial Biorealm page on the Parabasalia
Higher order taxa:
Description and Significance
Parabasalids (phylum Parabasalia) are anaerobic flagellated protists which contain at least one parabasal apparatus consisting of a parabasal body (Golgi complex) and a parabasal filament. Parabasalids can be distinguished by the presence of the microtubular axostyle-pelta complex, composed of a sheet of cross-linked microtubules that are the longitudinal axis of the cell. Trichomonas vaginalis is a parabasalid that causes a sexually transmitted disease in humans. Other parabasalid species live in the intestines of some cockroaches and termites, enabling them to break down the cellulose in the dead plant material they eat. These symbiotic parabasalids in turn have symbiotic bacteria that aid in locomotion and cellulose breakdown. The relationships of the parabasalids with their hosts and with other symbionts are complex and in most cases not well understood.
Parabasalids are the only eukaryotic lineage from which a sizeable number of genes have been examined without the detection of introns.
Cell Structure and Metabolism
Parabasalids are single-celled. All parabasalid genera studied to date lack mitochondria and peroxisomes, but have specialized organelles, called hydrogenosomes, in which anaerobic metabolism takes place. These microorganisms carry out a special type of closed mitosis called cryptopleuromitosis, characterized by the persistence of the nuclear envelope and the presence of an extra-nuclear spindle.
Parabasalids live as parasites or symbionts in animals, though a few are regarded as commensals (such as Trichomonas hominis and T. tenax).
| T. Vaginalis on the upper left, Termite gut symbionts on the upper right
Central and below is micrographs of parabasalid symbionts identified in the hindgut of Calotermes flavicollis (species of termite). A: Foaina dogieli; B: Hexamastix termitis; C: Tricercomitus divergens; D: Joenia annectens. Abbreviations: rf = recurrent flagellum; af = anterior flagella. Scale bars each represent 20 µm
Edgcomb, Virginia P., Delphine Gerbod, Christophe Noël, Eric Viscogliosi, and Pilar Delgado-Viscogliosi. "Phylogenetic position of parabasalid symbionts from the termite Calotermes flavicollis based on small subunit rRNA sequences." INTERNAT'L MICROBIOL (2000) 3:165–172 © Springer-Verlag Ibérica 2000.