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Malawimonas

Malawimonas O'Kelly & Nerad, 1999 (ref. ID; 7492 original paper)

Family Malawimonadidae (ref. ID; 7492 original paper)

[ref. ID; 7492]
Diagnosis; Malawimonads without loricas or other morphologically distinctive covering on cell or flagellar surfaces. Flagellate cells bacterivorous, ingesting prey near the posterior end of the ventral groove; permanently differentiated cytostome lacking. (ref. ID; 7492)
Notes; O'Kelly (O'Kelly 1993) argued that the jakobid flagellates are more similar to the retortamonads, amitochondriate flagellates normally found as hindgut commensals in animals (Brugerolle and Mignot 1990; Kulda and Nohynkova 1978), that to any other taxon of eukaryotes, with or without mitochondria. This assessment was based on those ultrastructural features, especially those associated with the flagellar vanes and the kinetids, that could be ascertained from the existing ultrastructural studies on retortamonads (Brugerolle 1991; Brugerolle and Mignot 1990). New information on retortamonad kinetid architecture has since been obtained for the free-living species Chilomastix cuspidata (Bernard, Simpson and Patterson 1997). Also, the genus Trimastix has been rediscoverd and found to have many retortamonad-like features (Brugerolle and Patterson 1997; O'Kelly, Farmer and Nerad 1999). Comparisons of these features (O'Kelly, Farmer and Nerad 1999) further support the idea that retortamonads, Trimastix and jakobids are similar, and may be closely-related taxa. Of greatest interest is the observation of shared features between Malawimonas and Trimastix on the one hand, and the Jakobidae, Histionidae and retortamonads on the other. Malawimonas and Trimastix possesss a prominent anterior root, lacking or very reduced in the other jakobids and retortamonads. Also, in the left ventral root of Malawimonas and Trimastix, microtubules are added to the inside of the ventral groove instead of the outside as in Jakoba, Histiona, Reclinomonas, and the retortamonads. The multilayered structure associated with the left ventral root in jakobids, histionids, and retortamonads is absent in Malawimonas and Trimastix. These observations suggest that jakobid flagellates belong to two clades, each of which includes metamonad, or metamonad-like, flagellates as well as jakobids. (ref. ID; 7492)
Etymology; "Malawi flagellate" (Malawi-, the African nation from which the type species was isolated; monas, Gk. "wanderer"). Malawimonas is a third declension feminine Latin noun. (ref. ID; 7492)
Type species; Malawimonas jakobiformis (ref. ID; 7492)
  1. Malawimonas jakobiformis O'Kelly & Nerad, 1999 (ref. ID; 7492 original paper) reported author and year? (ref. ID; 4980)

Malawimonas jakobiformis O'Kelly & Nerad, 1999 (ref. ID; 7492 original paper) reported author and year? (ref. ID; 4980)

Diagnosis

Freshwater protists with characteristics of genus, associated with lake sediments. Cell shape plastic, typically elongate, tapered at both ends, ventral surface planar to concave, dorsal surface convex. Flagellate cells 4.0-8.5 um in length, 2.0-4.5 um in width. Cysts 3.5-4.9 um diameter, spherical, with smooth wall, attached to substrate by pad to adhesive material. (ref. ID; 7492)

Descriptions

Remarks

Malawimonas jakobiformis has many features in common with other described members of the jakobid grade (Flavin and Nerad 1993; Mylnikov 1989; O'Kelly 1993, 1997; Patterson 1990). These organisms are biflagellate, heterotrophic, bacterivorous nanoflagellates characterized by a prominent ventral groove, two heterodynamic flagella of which the posteriormost resides in the ventral groove and has a single flagellar vane, and the lack of a persistent cytostome/cytopharynx complex. The flagellar vane character serves to separate jakobids, including M. jakobiformis, from all other protists. Only Colponema loxodes Stein has a single vane similar to that of jakobids (Mignot and Brugerolle 1975). This latter species is a large flagellate that preys on other eukaryotes rather than bacteria, and has prominent cortical alveolae, large structured extrusomes, a perinuclear Golgi body with its cis face adjacent to the nuclear envelope, and secondary cytoskeletal microtubules associated with at least one of the ventral roots (Mignot and Brugerolle 1975). All of these features separate C. loxodes from the jakobids (O'Kelly 1993). Retortamonads (Bernard, Simpson and Patterson 1997; Brugerolle 1991; Brugerolle and Mignot 1990) and Trimastix (Brugerolle and Patterson 1997; O'Kelly, Farmer and Nerad 1999) have two or three vanes on the posterior flagellum. Kinetid comparisons further reinforce the identification of M. jakobiformis with the jakobids. In particular, the ventral root microtubule configuration (a bifurcating left root, a bifurcating right root, and an intermediate singlet root, all proceeding alone the ventral groove parallel to the long axis of the cell to a juxtaposition point at the cell posterior) occurs elsewhere only in the amitochondriate retortamonad flagellates and Trimastix (Bernard, Simpson and Patterson 1997; Brugerolle 1991; Brugerolle and Patterson 1997; O'Kelly, Farmer and Nerad 1999), as described in more detail below. The pattern of cell division conforms to what has been observed in Reclinomonas and Jakoba (O'Kelly 1993), and preservation of kinetid elements in the M. jakobiformis cyst is consistent with what has been observed in Reclinomonas americana (O'Kelly 1997). In terms of external morphology, M. jakobiformis most closely resembles Jakoba libera; both species lack cell coverings and sessile trophic stages, swim in a similar manner, and share the tendency for the anterior flagellum to form a "crook". However, M. jakobiformis cannot be assigned to Jakoba, nor to any other genus of jakobids. Malawimonas jakobiformis has discoidal mitochondiral cristae; in Reclinomonas and Histiona, mitochondrial cristae are tubular, and in Jakoba they are irregularly flattened (O'Kelly 1993). The organelles tentatively identified as extrosomes in M. jakobiformis lack the structured contents of extrusomes (discobolocysts) in Jakoba (Patterson 1990), Reclinomonas (O'Kelly 1993, 1997), and Histiona (Mylnikov 1989). The posterior flagellar vane arises from a clearly defined point on the ventral surface of the flagellum in M. jakobiformis; in other jakobids, the vane has a diffuse origin along the dorsal surface (O'Kelly 1997). In M. jakobiformis, the dorsal fan microtubules arise in the vicinity of a two-stranded root emanating from the anterior basal body; in other jakobids, this root is absent, and the dorsal fan microtubules arise from the vicinity of the basal body itself (O'Kelly 1993, 1997). In M. jakobiformis, microtubules from the right root tend to be predominant in the floor of the ventral groove; in other jakobids, microtubules from the left root predominate (O'Kelly 1997). In M. jakobiformis, a few microtubules are added to the inside of the left ventral root, and the associated C fiber is short and lacks a lamellar substructure; in other jakobids, numerous microtubules are added to the outside of the left ventral groove, and the associated C fiber is longer and lamellate, forming a multilayered structure (O'Kelly 1993, 1997). These differences are at least as significant as are those that separate the jakobid families Jakobidae and Histionidae. Therefore, Malawimonas is placed in the Malawimonadidae n. fam. (ref. ID; 7492)

Etymology

"Resembling Jakoba" (jakobi-, the jakobid genus Jakoba, from Jakoba Ruinen, who described the species now called J. liera; formis, Gk. "form of"). (ref. ID; 7492)

Type locality

Chirombo Bay, Lake Nyasa, Malawi (14 degrees 5'S, 34 degrees 5'W). (ref. ID; 7492)

Type material

Holotype: Cryopreserved living material, conserved at the American Type Culture Collection (ATCC) as strain 50310. Protargol-stained slides and resin-embedded cells derived from strain 50310 conserved at ATCC and the Natural History Museum, Smithsonian Institution, accession number USNM 51468. (ref. ID; 7492)

Internet data dissemination

Updated summaries of the morphology, taxonomy, and biology of M. jakobiformis appear on the Protist Image Data Web site (http://megasun.bch.umontreal.ca/protists/malawi/). (ref. ID; 7492)