Possible Mitochondria-Related Organelles in Poorly-Studied “Amitochondriate” Eukaryotes

Hampl, Vladimı́r; Simpson, Alastair G. B.

doi:10.1007/7171_2007_107

Cited by 16 publications

(9 citation statements)

References 62 publications

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“…In place of classical‐looking mitochondria, our new isolate has rounded organelles that lack cristae. This is similar to other Fornicata, but also to Preaxostyla and Parabasala, none of which have classical crista‐bearing mitochondrial organelles (Brugerolle and Patterson 1997; Carpenter, Waller, and Keeling 2008; Hampl and Simpson 2008; O'Kelly, Farmer, and Nerad 1999; Simpson and Patterson 1999; Yubuki et al 2007). In summary, both molecular phylogenies and easy‐to‐interpret morphological characters indicate that our new isolate belongs to the taxon Fornicata.…”

Section: Discussionsupporting

confidence: 73%

Light Microscopic Observations, Ultrastructure, and Molecular Phylogeny of Hicanonectes teleskopos n. g., n. sp., a Deep‐Branching Relative of Diplomonads

Park

Kolísko

Heiss

et al. 2009

J Eukaryotic Microbiology

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We describe Hicanonectes teleskopos n. g., n. sp., a heterotrophic flagellate isolated from low-oxygen marine sediment. Hicanonectes teleskopos has a ventral groove and two unequal flagella, and rapidly rotates during swimming. At the ultrastructural level H. teleskopos is a "typical excavate": it displays flagellar vanes, a split right microtubular root, "I,""B," and "C" fibres, a singlet microtubular root, and a possible composite fibre. Small subunit rRNA (SSU rRNA) gene phylogenies and an "arched" B fibre demonstrate that H. teleskopos belongs to Fornicata (i.e. diplomonads, retortamonads, and relatives). It forms a clade with the deep-branching fornicate Carpediemonas, with moderate-to-strong bootstrap support, although their SSU rRNA gene sequences are quite dissimilar. Hicanonectes differs from Carpediemonas in cell shape, swimming behaviour, number of basal bodies (i.e. 4 vs. 3), number of flagellar vanes (i.e. 2 vs. 3), anterior root organization, and by having a cytopharynx. Like Carpediemonas and Dysnectes, Hicanonectes has conspicuous mitochondrion-like organelles that lack cristae and superficially resemble the hydrogenosomes of parabasalids, rather than the mitosomes of their closer relatives the diplomonads (e.g. Giardia).

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Section: Discussionsupporting

confidence: 73%

Light Microscopic Observations, Ultrastructure, and Molecular Phylogeny of Hicanonectes teleskopos n. g., n. sp., a Deep‐Branching Relative of Diplomonads

Park

Kolísko

Heiss

et al. 2009

J Eukaryotic Microbiology

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“…6 This functional reduction can be linked to the loss of the mitochondrial genome [7][8][9][10] and is strongly correlated with structural simplification, making the most reduced MROs small and difficult to identify or recognize. 11,12 In only one known instance has the mitochondrion been lost altogether. 13 In apicomplexan parasites, such as the well-studied and medically important pathogens, Plasmodium spp.…”

Section: Resultsmentioning

confidence: 99%

“…Functional reduction in MROs is usually accompanied by structural reduction, including the loss of hallmark features of mitochondria, such as cristae. 6,12,48 But this does not appear to apply to gregarines, where those examined at the ultrastructural level are generally found to contain conspicuous mitochondria with distinctive apicomplexan tubular cristae (refer to Table S1 for a summary of transmission electron microscopy [TEM] studies). Although there is variability in these studies, it is limited and does not clearly correspond to functional reduction: indeed, the most structural variability is between species of Selenidium, which all contain a complete respiratory chain (Table S1).…”

Section: Cryptosporidium Hominis*mentioning

confidence: 99%

Parallel functional reduction in the mitochondria of apicomplexan parasites

2021

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“…[51]) to apparent intermediates between hydrogenosomes and mitosomes (e.g., Mastigamoeba [21] and Trimastix [25]). The potential functional diversity of MROs could even be greater since there are a myriad of additional poorly studied anaerobic protists that, in transmission electron microscopy studies (26), have been shown to contain MROlike structures that have yet to be intensively investigated. By studying their organelles, we can obtain important insights into their evolutionary origin, the range of their biochemical flexibility within the eukaryotic tree of life, and possibly even the origin of eukaryotes themselves (5).…”

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confidence: 99%

Sawyeria marylandensis (Heterolobosea) Has a Hydrogenosome with Novel Metabolic Properties

et al. 2010

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Protists that live under low-oxygen conditions often lack conventional mitochondria and instead possess mitochondrion-related organelles (MROs) with distinct biochemical functions. Studies of mostly parasitic organisms have suggested that these organelles could be classified into two general types: hydrogenosomes and mitosomes. Hydrogenosomes, found in parabasalids, anaerobic chytrid fungi, and ciliates, metabolize pyruvate anaerobically to generate ATP, acetate, CO 2 , and hydrogen gas, employing enzymes not typically associated with mitochondria. Mitosomes that have been studied have no apparent role in energy metabolism. Recent investigations of free-living anaerobic protists have revealed a diversity of MROs with a wider array of metabolic properties that defy a simple functional classification. Here we describe an expressed sequence tag (EST) survey and ultrastructural investigation of the anaerobic heteroloboseid amoeba Sawyeria marylandensis aimed at understanding the properties of its MROs. This organism expresses typical anaerobic energy metabolic enzymes, such as pyruvate:ferredoxin oxidoreductase, [FeFe]-hydrogenase, and associated hydrogenase maturases with apparent organelle-targeting peptides, indicating that its MRO likely functions as a hydrogenosome. We also identified 38 genes encoding canonical mitochondrial proteins in S. marylandensis, many of which possess putative targeting peptides and are phylogenetically related to putative mitochondrial proteins of its heteroloboseid relative Naegleria gruberi. Several of these proteins, such as a branched-chain alpha keto acid dehydrogenase, likely function in pathways that have not been previously associated with the well-studied hydrogenosomes of parabasalids. Finally, morphological reconstructions based on transmission electron microscopy indicate that the S. marylandensis MROs form novel cup-like structures within the cells. Overall, these data suggest that Sawyeria marylandensis possesses a hydrogenosome of mitochondrial origin with a novel combination of biochemical and structural properties.It is now widely accepted that the most recent common ancestor of extant eukaryotes possessed an endosymbiont-derived mitochondrial organelle of alphaproteobacterial ancestry (see reference 16 for a recent review). Although most wellknown eukaryotes contain mitochondria that aerobically respire to produce ATP, a vast diversity of anaerobic eukaryotic lineages have been discovered that lack classical mitochondrial structures. Instead of mitochondria, biochemically diverse double-membrane-bounded organelles have been found that function under low-oxygen conditions (for recent reviews, see references 5, 6, 17, 23, 54, and 57). The discovery and recent investigations of the functions of these mitochondrion-related organelles (MROs) has greatly expanded our understanding of both the conservation and diversity of functions that these organelles can perform.A number of protist lineages, including the parabasalids, several anaerobic ciliate groups, and anaerobic chy...

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Possible Mitochondria-Related Organelles in Poorly-Studied “Amitochondriate” Eukaryotes

Cited by 16 publications

References 62 publications

Light Microscopic Observations, Ultrastructure, and Molecular Phylogeny of Hicanonectes teleskopos n. g., n. sp., a Deep‐Branching Relative of Diplomonads

Light Microscopic Observations, Ultrastructure, and Molecular Phylogeny of Hicanonectes teleskopos n. g., n. sp., a Deep‐Branching Relative of Diplomonads

Parallel functional reduction in the mitochondria of apicomplexan parasites

Sawyeria marylandensis (Heterolobosea) Has a Hydrogenosome with Novel Metabolic Properties

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