Malawimonas O'Kelly & Nerad 1999

Introduction

Characteristics

Malawimonads are free-swimming heterotrophic flagellates.  They are small, typically about 5 μm long (Malawimonas jakobiformis is 4-8.5 μm - O'Kelly and Nerad, 1999).  Cells are bean-shaped, with two flagella and a ventral groove (O’Kelly and Nerad, 1999; Simpson unpublished).  Like other small free-living excavates, malawimonads use the groove to collect and phagocytose small food particles (prokaryotes) that are transported on a current generated by the posterior flagellum.  Malawimonads have been cultured from freshwater sediments and soil (O’Kelly and Nerad 1999; Ekelund 2002, under the name Carpediemonas sp. – Simpson, unpublished).   Malawimonas jakobiformis forms cysts (O’Kelly and Nerad, 1999).

Malawimonads closely resemble other small excavate free-living excavates when viewed under the light microscope, in particular deep-branching members of Fornicata, namely Carpediemonas and Dynectes (from which they are almost indistinguishable), and non-loricate jakobids such as Jakoba and Andalucia.  Ultrastructural examination indicates that malawimonads differ from these other small excavates by having discoidal mitochondrial cristae (O’Kelly, 1993; O’Kelly and Nerad, 1999; Simpson, unpublished).  By contrast, jakobids have tubular or flat cristae (O’Kelly, 1993; Lara et al., 2006) while the mitochondrion-like organelles of Carpediemonas and Dysnectes lack cristae (Simpson and Patterson, 1999; Yubuki et al. 2007).  Malawimonas jakobiformis has a single vane on its posterior flagellum that is located on the ventral side of the axoneme, rather than the dorsal side of the axoneme, as is characteristic for jakobids (O’Kelly and Nerad, 1999).  Malawimonads lack the other synapomorphies of jakobids, and also lack the diagnostic arched fibre synapomorphy for Fornicata (O’Kelly and Nerad, 1999; Simpson, unpublished – see Simpson and Patterson, 1999, 2001; Yubuki et al. 2007; Simpson, 2003).  

The mitochondrial genomes of Malawimonas jakobiformis and ‘Malawimonas californiana’ have been sequenced (Lang et al., 1999; Gray et al., 2004).  The Malawimonas mitochondrial genomes are relatively gene-rich, with ~70 total unique genes and ORFs (Lang et al., 1999).  Three ORFs are unique to Malawimonas, while three of the genes for ribosomal proteins are otherwise only known from jakobid mitochondrial genomes (Gray et al., 2004).  Other than these three genes, Malawimonas lacks most of the unusual ‘bacterial-like’ features of jakobid mitochondrial genomes, including genes for eubacterial-type RNA polymerase subunits (Gray et al., 2004).

Other Names for Malawimonas O'Kelly & Nerad 1999

• Malawimonads
• Malawimonadidae O'Kelly & Nerad 1999

References

Ekelund F. (2002) Tolerance of soil flagellates to increased NaCl levels. J. Eukaryot. Microbiol. 49: 324-328.

Gray, M. W., Lang, B. F. & Burger, G. (2004) Mitochondria of protists. Annu. Rev. Genet. 38: 477-525.

Lang, B. F., Gray, M.W., & Burger, G. (1999) Mitochondrial genome evolution and the origin of eukaryotes. Annu. Rev. Genet. 33: 351-397.

Lara, E., Chatzinotas, A., Simpson, A.G.B. (2006) Andalucia (gen. nov,): a new taxon for the deepest branch within jakobids (Jakobida; Excavata), based on morphological and molecular study of a new flagellate from soil. J. Eukaryot. Microbiol. 53: 112-120.

O’Kelly, C. J. (1993) The jakobid flagellates: structural features of Jakoba, Reclinomonas and Histiona and implications for the early diversification of eukaryotes. J. Eukaryot. Microbiol. 40: 627--636.

O’Kelly, C.J. & Nerad, T.A. (1999) Malawimonas jakobiformis n. gen., n. sp. (Malawimonadidae n. fam.): A jakoba-like heterotrophic nanoflagellate with discoidal mitochondrial cristae. J. Eukaryot. Microbiol. 46: 522-531.

Simpson, A.G.B. (2003) Cytoskeletal organisation phylogenetic affinities and systematics in the contentious taxon Excavata (Eukaryota). Int. J. Syst. Evol. Microbiol. 53: 1759-1777.

Simpson, A.G.B. & Patterson, D.J. (1999) The ultrastructure of Carpediemonas membranifera (Eukaryota) with reference to the “excavate hypothesis”. Europ. J. Protistol. 35: 353-370.

Simpson, A.G.B. & Patterson, D.J. (2001) On core jakobids and excavate taxa: the ultrastructure of Jakoba incarcerata. J. Eukaryot. Microbiol. 48: 480-492.

Yubuki, N., Inagaki, Y., Nakayama, T., Inouye, I., (2007) Ultrastructure and ribosomal RNA phylogeny of the free-living heterotrophic flagellate Dysnectes brevis n. gen., n. sp., a new member of the Fornicata. J. Eukaryot. Microbiol. 54: 191-200.

Information on the Internet

• Protist Image Database page for Malawimonas.
• OGMP Malawimonas mitochondrial genome page.