Variation and Evolution in Plants and Microorganisms Toward a New Synthesis 50 Years After Stebbins (2000) / Chapter Skim
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3 The Chimeric Eukaryote: Origin of the Nucleus from the Karyomastigont in Amitochondriate Protists
3 The Chimeric Eukaryote: Origin of the Nucleus from the Karyomastigont in Amitochondriate Protists
Pages 21-34
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From page 21... ...
Selection pressure for speed swimming and oxygen avoidance led to an ancient analogue of the extant cosmopolitan bacterial consortium "Thiodendron latens." By eubacterial-archaebacterial genetic integration, the chimera, an amitochondriate heterotroph, evolved. This "earliest branching protist" that formed by permanent DNA recombination generated the nucleus as a component of the karyomastigont, an intracellular complex that assured genetic continuity of the former symbionts.
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From page 22... ...
An advantage of our model includes its simultaneous consistency in the evolutionary scenario across fields of science: cell biology, developmental biology, ecology, genetics, microbiology, molecular evolution, paleontology, protistology. Environmentally plausible habitats and modern taxa are easily comprehensible as legacies of the fusion event.
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From page 23... ...
The tubulin-actin motility systems of feeding and sexual cell fusion facilitate frequent viable incorporation of heterologous nucleic acid. Many eukaryotes, but no prokaryotes, regularly ingest entire cells, including, of course, their genomes, in a single phagocytotic event.
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From page 24... ...
and oxidation of the sulfide to elemental sulfur by the eubacterium generated carbon-rich fermentation products and electron acceptors for the archaebacterium. When swimming eubacteria attached to the archaebacterium, the likelihood that the consortium efficiently reached its carbon sources was enhanced.
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25 .a ~ ~ o o s t o E ~ ao o ~ r— ~ o ao o ~ Q _ _ ~ ~ \ 4, f .f ~ f ~ ~ .0 ~ E E ~ ~ ° ~ ao ao ~ ~ s E o E o cn ~ ~ .m cn rs Q .
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Isolations from Staraya Russa mineral spring 8, mineral spring Serebryani, Lake Nizhnee, mudbaths; littoral zone at the White Sea strait near Veliky Island, Gulf of Nilma; Pacific Ocean hydrothermal habitats at the Kurile Islands and Kraternaya Bay; Matupi Harbor Bay, Papua New Guinea, etc. (Dubinina et al., 1993a)
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From page 27... ...
435) , reported that "the pattern of bacterial growth changes drastically when the redox potential of the medium is brought down by addition of 500 mg/1 of sodium sulfide." The differential growth of the two tightly associated partners in the consortium imitates the purported Thiodendron bacterial developmental patterns.
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From page 28... ...
, many interactions inside the chimera generated protists in which mitosis and eventually meiotic sexuality evolved. The key concept here is that the karyomastigont, retained by amitochondriate protists and later by their mitochondriate descendants, is the morphological manifestation of the original archaebacterial-eubacterial fused genetic system.
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From page 29... ...
That mitochondria were never acquired in the ancestors we consider more likely than that they were lost in every species of these anaerobic protists. Eubacterial genes in the nucleus that are not from the original spirochete probably were acquired in amitochondriate protists from proteobacterial symbionts other than those of the mitochondrial lineage.
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From page 30... ...
In trophic forms of protists that lack mastigote stages, the Karyomastigont is generally absent. An exception is Histomonas, an amoeboid trichomonad cell that lacks an axoneme but bears enough of the remnant Karyomastigont structure to permit its classification with parabasalids rather than with rhizopod amoebae (Dyer, 1990~.
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From page 31... ...
, Ugo d'Ambrosio, Donna Reppard, Dennis Searcy, and Andrew Wier. We acknowledge research assistance from the University of Massachusetts Graduate School via Linda Slakey, Dean of Natural Science and Mathematics, from the Richard Lounsbery Foundation, and from the American Museum of Natural History Department of Invertebrates (New York)
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From page 32... ...
32 Q o S s At A o CD o ~n A ~n Q Aria O ~ .' V, -\i -5 .~ o C)
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(2000) Molecular phylogeny of Parabasalids based on small subunit rRNA sequences, with emphasis on the Trichomonadinae subfamily.
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From page 34... ...
(1980) Thermoplasma acidophilum histone-like protein: partial amino acid sequence suggestive of homology to eukaryotic histones.
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