Lynn Margulis，gaea，symbiogenesis

傻傻笑(专注天体生物学的研究) 组长

2011-11-24 11:30:12

Lynn Margulis, Renowned Evolutionary Biologist and Author at UMass Amherst, Dead at 73 Nov. 23, 2011 AMHERST, Mass. - Internationally renowned evolutionary biologist and author Lynn Margulis, a Distinguished University Professor of Geosciences at the University of Massachusetts Amherst and a National Medal of Science recipient, died Nov. 22 at her home in Amherst. She was 73. Margulis was best known for her theory of symbiogenesis, which challenges central tenets of neo-Darwinism. She argued that inherited variation, significant in evolution, does not come mainly from random mutations. Rather, new tissues, organs, and even new species evolve primarily through the long-lasting intimacy of strangers. The fusion of genomes in symbioses followed by natural selection, she suggests, leads to increasingly complex levels of individuality. Margulis was also acknowledged for her contribution to James E. Lovelock’s Gaia concept. Gaia theory posits that the Earth’s surface interactions among living beings sediment, air, and water have created a vast self-regulating system. "She leaves us a legacy of academic accomplishment brought about by her original thought and tireless inquiry into multiple fields of science that look at how the world functions and how that magnificent world has developed over time," said UMass Amherst Chancellor Robert C. Holub. "Her passing is a great loss for the entire campus family." "She was an amazing scientist and a wonderful person," said Steve Goodwin, dean of the College of Natural Sciences at UMass Amherst. "Of course she was a different kind of scientist, one who does not come along very often. Her great gift was making connections, connections that others just couldn’t make. She provided a stimulation to the campus community and the scientific community that was uniquely her own." R. Mark Leckie, head of the geosciences department at UMass Amherst, said, "She will be dearly missed by her devoted students and her many friends and colleagues around the world." Margulis joined the faculty as a Distinguished University Professor in 1988 after teaching at Boston University for 22 years. Her publications span topics from cell biology to microbial evolution. Margulis authored and co-authored hundreds of research papers, reviews, non-technical articles and many books, including "Symbiotic Planet: A New Look at Evolution" and "Acquiring Genomes: A Theory of the Origin of the Species." Most recently, with UMass Amherst alumnus Michael J. Chapman, she wrote "Kingdoms & Domains: An Illustrated Guide to the Phyla of Life on Earth." Several of her books were co-authored by her son, Dorion Sagan. In 1998, the Library of Congress announced that it would permanently archive her papers. She was elected to the National Academy of Sciences in 1983 and received the National Medal of Science from President Bill Clinton in 1999. She was also a member of the American Academy of Arts and Sciences (AAAS) and the World Academy of Art and Science, an elected foreign member of the Russian Academy of Natural Sciences, and a fellow of the Massachusetts Academy of Sciences. Her numerous awards and honors included the 2009 Darwin-Wallace Medal, awarded at 50-year intervals by the London-based Linnean Society for significant advances in the study of natural history and evolution, according to the society. She also received the Nevada Medal, Sigma Xi’s William Proctor Prize, a NASA Public Service Award, the Miescher-Ishida Prize, the Commandeur de l’Ordre des Palmes Academiques de France, Guggenheim, Rockefeller Bellagio and Sherman Fairchild fellowships and many honorary degrees. On campus, she received the Chancellor’s Medal and the Award for Outstanding Accomplishments in Research and Creative Activity, given in 2009. Margulis was also the co-founder of two international societies, Evolutionary Protistology (ISEP) and Symbiosis (ISS). She served on committees for the National Academy of Sciences, NASA, AAAS and the National Science Resource Center. She lectured widely in the U.S. and abroad, including Europe, Cuba, Israel, Japan and Mexico. Born in Chicago, she was a 1957 graduate of the University of Chicago, where she enrolled at the age of 14. She went on to earn an M.S. in genetics and zoology at the University of Wisconsin in 1960 and a Ph.D. in genetics at the University of California, Berkeley, in 1965. She leaves her children Dorion Sagan, Jeremy Sagan, Zachary Margulis-Ohnuma and Jennifer Margulis di Properzio; daughters-in-law Robin Kolnicki and Mary Margulis-Ohnuma; son-in-law James di Properzio; grandchildren Tonio, Sarah, Hesperus, Athena, Etani, Leone, Miranda, Atticus and Madeline; her sisters Joan Glashow, Sharon Kleitman and Diane Alexander; her beloved dog Menina, and her wide circle of family and friends. http://www.umass.edu/newsoffice/newsreleases/articles/141605.php

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  傻傻笑 (专注天体生物学的研究) 组长 楼主 2011-11-24 11:32:09

  Symbiogenesis From Wikipedia, the free encyclopedia Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species, which proposed that chloroplasts originate from cyanobacteria captured by a protozoan.[1] Ivan Wallin also supported this concept in his book “Symbionticism and the Origins of Species." He suggested that bacteria might be the cause of the origin of species, and that species creation may occur through endosymbiosis. Today both chloroplasts and mitochondria are believed to have such an origin; this is the endosymbiotic theory. In Acquiring Genomes: A Theory of the Origins of Species, biologist Lynn Margulis argued later that symbiogenesis is a primary force in evolution. According to her theory, acquisition and accumulation of random mutations are not sufficient to explain how inherited variations occur; rather, new organelles, bodies, organs, and species arise from symbiogenesis.[2] Whereas the classical interpretation of evolution (the modern evolutionary synthesis) emphasizes competition as the main force behind evolution, Margulis emphasizes cooperation.[3] She argues that bacteria along with other microorganisms helped create the conditions that we require for life, such as oxygen. Margulis believes that these microorganisms make up a major component in Earth’s biomass and that they are the reason current conditions on earth are maintained. She also believes that the DNA in the cytoplasm of animal, plant, fungal and protist cells, rather than resulting from mutations, resulted from genes from bacteria that became organelles. She claimed that bacteria are able to exchange genes more quickly and more easily, and because of this, they are more versatile, which is why life was able to evolve so quickly.[4] A fundamental principle of modern evolutionary theory is that mutations arise one at a time and either spread through the population or not, depending on whether they offer an individual fitness advantage. Nevertheless, this general case may not apply to all examples of evolutionary change. Indeed, genome mapping techniques have revealed that family trees of the major taxa appear to be extensively cross-linked—possibly due to lateral gene transfer.[5] Contents [hide] 1 See also 2 Citations 3 References 4 Important publications [edit] See alsoViral eukaryogenesis [edit] Citations1.^ Sapp J, Carrapiço F, Zolotonosov M (2002). "Symbiogenesis: the hidden face of Constantin Merezhkowsky". History and philosophy of the life sciences 24 (3–4): 413–40. doi:10.1080/03919710210001714493. PMID 15045832. 2.^ Margulis L (1993). "Origins of species: acquired genomes and individuality". BioSystems 31 (2–3): 121–5. doi:10.1016/0303-2647(93)90039-F. PMID 8155844. 3.^ Margulis L, Bermudes D (1985). "Symbiosis as a mechanism of evolution: status of cell symbiosis theory". Symbiosis 1: 101–24. PMID 11543608. 4.^ "Acquiring Genomes". March 8. http://www.isepp.org/sj0506.html. Retrieved February 24, 2011 5.^ de la Cruz F, Davies J (2000). "Horizontal gene transfer and the origin of species: lessons from bacteria". Trends Microbiol. 8 (3): 128–33. doi:10.1016/S0966-842X(00)01703-0. PMID 10707066. [edit] ReferencesSapp J, Carrapiço F, Zolotonosov M (2002). "Symbiogenesis: the hidden face of Constantin Merezhkowsky". History and philosophy of the life sciences 24 (3–4): 413–40. doi:10.1080/03919710210001714493. PMID 15045832. Margulis L (1993). "Origins of species: acquired genomes and individuality". BioSystems 31 (2–3): 121–5. doi:10.1016/0303-2647(93)90039-F. PMID 8155844. Margulis L, Bermudes D (1985). "Symbiosis as a mechanism of evolution: status of cell symbiosis theory". Symbiosis 1: 101–24. PMID 11543608. "Acquiring Genomes". March 8. http://www.isepp.org/sj0506.html. Retrieved February 24, 2011 de la Cruz F, Davies J (2000). "Horizontal gene transfer and the origin of species: lessons from bacteria". Trends Microbiol. 8 (3): 128–33. doi:10.1016/S0966-842X(00)01703-0. PMID 10707066. [edit] Important publicationsKonstantin Mereschkowsky. Symbiogenesis and the Origin of Species. 1926. Lynn Margulis. Symbiotic Planet: A New Look at Evolution. Amherst, MA: Perseus Books Group, 1998. ISBN 0-456-07271-2. Lynn Margulis, Dorion Sagan. Acquiring Genomes: A Theory of the Origins of Species. Amherst, MA: Perseus Books Group, 2002. ISBN 0-465-04391-7. http://en.wikipedia.org/wiki/Symbiogenesis

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  傻傻笑 (专注天体生物学的研究) 组长 楼主 2011-11-24 15:21:21

  Endosymbiotic theory From Wikipedia, the free encyclopedia Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranesThe endosymbiotic theory concerns the mitochondria, plastids (e.g. chloroplasts), and possibly other organelles of eukaryotic cells. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts. Mitochondria developed from proteobacteria (in particular, Rickettsiales, the SAR11 clade,[1][2] or close relatives) and chloroplasts from cyanobacteria. Contents [hide] 1 History 2 Evidence 3 Secondary endosymbiosis 4 Problems 5 See also 6 Notes 7 References 8 External links [edit] History Endosymbiotic theoryThe endosymbiotic (from the Greek: endo- meaning inside and -symbiosis meaning cohabiting) theory was first articulated by the Russian botanist Konstantin Mereschkowski in 1905.[3] Mereschkowski was familiar with work by botanist Andreas Schimper, who had observed in 1883 that the division of chloroplasts in green plants closely resembled that of free-living cyanobacteria, and who had himself tentatively proposed (in a footnote) that green plants had arisen from a symbiotic union of two organisms.[4] Ivan Wallin extended the idea of an endosymbiotic origin to mitochondria in the 1920s.[5] These theories were initially dismissed or ignored. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example studies by Hans Ris[6]), combined with the discovery that plastids and mitochondria contain their own DNA[7] (which by that stage was recognized to be the hereditary material of organisms) led to a resurrection of the idea in the 1960s. The endosymbiotic theory was advanced and substantiated with microbiological evidence by Lynn Margulis in a 1967 paper, The Origin of Mitosing Eukaryotic Cells.[8] In her 1981 work Symbiosis in Cell Evolution she argued that eukaryotic cells originated as communities of interacting entities, including endosymbiotic spirochaetes that developed into eukaryotic flagella and cilia. This last idea has not received much acceptance, because flagella lack DNA and do not show ultrastructural similarities to bacteria or archaea. See also Evolution of flagella. According to Margulis and Dorion Sagan,[9] "Life did not take over the globe by combat, but by networking" (i.e., by cooperation). The possibility that peroxisomes may have an endosymbiotic origin has also been considered, although they lack DNA. Christian de Duve proposed that they may have been the first endosymbionts, allowing cells to withstand growing amounts of free molecular oxygen in the Earth's atmosphere. However, it now appears that they may be formed de novo, contradicting the idea that they have a symbiotic origin.[10] It is believed that over millennia these endosymbionts transferred some of their own DNA to the host cell's nucleus during the evolutionary transition from a symbiotic community to an instituted eukaryotic cell (called "serial endosymbiosis"). [edit] EvidenceEvidence that mitochondria and plastids arose from bacteria is as follows:[11][12][13] New mitochondria and plastids are formed only through a process similar to binary fission. In some algae, such as Euglena, the plastids can be destroyed by certain chemicals or prolonged absence of light without otherwise affecting the cell. In such a case, the plastids will not regenerate. This shows that the plastic regeneration relies on an extracellular source, such as from cell division or endosymbiosis. They are surrounded by two or more membranes, and the innermost of these shows differences in composition from the other membranes of the cell. They are composed of a peptidoglycan cell wall characteristic of a bacterial cell. Both mitochondria and plastids contain DNA that is different from that of the cell nucleus and that is similar to that of bacteria (in being circular in shape and in its size). DNA sequence analysis and phylogenetic estimates suggest that nuclear DNA contains genes that probably came from plastids. These organelles' ribosomes are like those found in bacteria (70S). Proteins of organelle origin, like those of bacteria, use N-formylmethionine as the initiating amino acid. Much of the internal structure and biochemistry of plastids, for instance the presence of thylakoids and particular chlorophylls, is very similar to that of cyanobacteria. Phylogenetic estimates constructed with bacteria, plastids, and eukaryotic genomes also suggest that plastids are most closely related to cyanobacteria. Mitochondria have several enzymes and transport systems similar to those of bacteria. Some proteins encoded in the nucleus are transported to the organelle, and both mitochondria and plastids have small genomes compared to bacteria. This is consistent with an increased dependence on the eukaryotic host after forming an endosymbiosis. Most genes on the organellar genomes have been lost or moved to the nucleus. Most genes needed for mitochondrial and plastid function are located in the nucleus. Many originate from the bacterial endosymbiont. Plastids are present in very different groups of protists, some of which are closely related to forms lacking plastids. This suggests that if chloroplasts originated de novo, they did so multiple times, in which case their close similarity to each other is difficult to explain. Many of these protists contain "primary" plastids that have not yet been acquired from other plastid-containing eukaryotes. Among eukaryotes that acquired their plastids directly from bacteria (known as Archaeplastida), the glaucophyte algae have chloroplasts that strongly resemble cyanobacteria. In particular, they have a peptidoglycan cell wall between the two membranes. Mitochondria and plastids are similar in size to bacteria. [edit] Secondary endosymbiosisPrimary endosymbiosis involves the engulfment of a bacterium by another free living organism. Secondary endosymbiosis occurs when the product of primary endosymbiosis is itself engulfed and retained by another free living eukaryote. Secondary endosymbiosis has occurred several times and has given rise to extremely diverse groups of algae and other eukaryotes. Some organisms can take opportunistic advantage of a similar process, where they engulf an alga and use the products of its photosynthesis, but once the prey item dies (or is lost) the host returns to a free living state. Obligate secondary endosymbionts become dependent on their organelles and are unable to survive in their absence (for a review see McFadden 2001[14]). RedToL, the Red Algal Tree of Life Initiative funded by the National Science Foundation highlights the role red algae or Rhodophyta played in the evolution of our planet through secondary endosymbiosis. One possible secondary endosymbiosis in process has been observed by Okamoto & Inouye (2005). The heterotrophic protist Hatena behaves like a predator until it ingests a green alga, which loses its flagella and cytoskeleton, while Hatena, now a host, switches to photosynthetic nutrition, gains the ability to move towards light and loses its feeding apparatus. The process of secondary endosymbiosis left its evolutionary signature within the unique topography of plastid membranes. Secondary plastids are surrounded by three (in euglenophytes and some dinoflagellates) or four membranes (in haptophytes, heterokonts, cryptophytes, and chlorarachniophytes). The two additional membranes are thought to correspond to the plasma membrane of the engulfed alga and the phagosomal membrane of the host cell. The endosymbiotic acquisition of a eukaryote cell is represented in the cryptophytes; where the remnant nucleus of the red algal symbiont (the nucleomorph) is present between the two inner and two outer plastid membranes.[citation needed] Despite the diversity of organisms containing plastids, the morphology, biochemistry, genomic organisation, and molecular phylogeny of plastid RNAs and proteins suggest a single origin of all extant plastids – although this theory is still debated.[15][16] Some species including Pediculus humanus have multiple chromosomes in the mitochondrion. This and the pylogenetics of the genes encoded within the mitochondrion suggests that the ancestors of mitochondria may have been acquired on several occasions rather than just once.[17] [edit] Problems This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2009) Neither mitochondria nor plastids can survive in oxygen or outside the cell, having lost many essential hormones required for survival. The standard counterargument points to the large timespan that the mitochondria/plastids have co-existed with their hosts. In this view, genes and systems that were no longer necessary were simply deleted, or in many cases, transferred into the host genome instead. (In fact these transfers constitute an important way for the host cell to regulate plastid or mitochondrial activity.) For example, most plastids are not able to produce respiratory proteins necessary for respiration. Like many living cells, plastids would die if energy is not provided to them by respiration. A large cell, especially one equipped for phagocytosis, has vast energetic requirements, which cannot be achieved without the internalisation of energy production (due to the decrease in the surface area to volume ratio as size increases). This implies that, for the cell to gain mitochondria, it could not have been a eukaryote, and must have been a bacterium. This in turn implies that the emergence of the eukaryotes and the formation of mitochondria were achieved simultaneously. This may be explained by possibly a very close symbiotic relationship between two types of bacteria which eventually led to gene exchange and engulfing of the mitochondria precursors through partial fusion or engulfing by the host bacteria. Genetic analysis of small eukaryotes that lack mitochondria shows that they all still retain genes for mitochondrial proteins. This implies that all these eukaryotes once had mitochondria. This objection can be answered if, as suggested above, the origin of the eukaryotes coincided with the formation of mitochondria. Alternatively, we may postulate extinction of all other descendants of a mitochondrion-free ancestral eukaryote, perhaps due to competition from the symbiotic clade, or oxygen poisoning as levels continued to rise. These last two problems are accounted for in the Hydrogen hypothesis. [edit] See also Hatena Lichen Symbiogenesis Transfer of mitochondrial and chloroplast DNA to the nucleus Viral Eukaryogenesis (hypothesis that the cell nucleus originated from endosymbiosis). Protobiont Numt Hydrogen hypothesis James A. Lake [edit] Notes1.^ "Mitochondria Share an Ancestor With SAR11, a Globally Significant Marine Microbe". ScienceDaily. July 25, 2011. http://www.sciencedaily.com/releases/2011/07/110725190046.htm. Retrieved 2011-07-26. 2.^ J. Cameron Thrash et al. (2011). "Phylogenomic evidence for a common ancestor of mitochondria and the SAR11 clade". Scientific Reports. doi:10.1038/srep00013. 3.^ Mereschkowski C (1905). "Über Natur und Ursprung der Chromatophoren im Pflanzenreiche". Biol Centralbl 25: 593–604. 4.^ Schimper AFW (1883). "Über die Entwicklung der Chlorophyllkörner und Farbkörper". Bot. Zeitung 41: 105–14, 121–31, 137–46, 153–62. 5.^ Wallin IE (1923). "The Mitochondria Problem". The American Naturalist 57 (650): 255–61. doi:10.1086/279919. 6.^ Ris H, Singh RN (January 1961). "Electron microscope studies on blue-green algae". J Biophys Biochem Cytol 9 (1): 63–80. doi:10.1083/jcb.9.1.63. PMC 2224983. PMID 13741827. http://www.jcb.org/cgi/pmidlookup?view=long&pmid=13741827. 7.^ Stocking C and Gifford E (1959). "Incorporation of thymidine into chloroplasts of Spirogyra". Biochem. Biophys. Res. Comm. 1 (3): 159–64. doi:10.1016/0006-291X(59)90010-5. 8.^ Lynn Sagan (1967). "On the origin of mitosing cells". J Theor Bio. 14 (3): 255–274. doi:10.1016/0022-5193(67)90079-3. PMID 11541392. 9.^ Margulis, Lynn; Sagan, Dorion (2001). "Marvellous microbes". Resurgence 206: 10–12. 10.^ Gabaldón T, Snel B, van Zimmeren F, Hemrika W, Tabak H, Huynen MA (2006). "Origin and evolution of the peroxisomal proteome". Biol. Direct 1 (1): 8. doi:10.1186/1745-6150-1-8. PMC 1472686. PMID 16556314. http://www.biology-direct.com/content/1//8. (Provides evidence that contradicts an endosymbiotic origin of peroxisomes. Instead it is suggested that they evolutionarily originate from the Endoplasmic Reticulum) 11.^ [1] Kimball, J. 2010. Kimball's Biology Pages. Accessed October 13, 2010. An online open source biology text by Harvard professor, and author of a general biology text, John W. Kimball. 12.^ Reece, J., Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson, 2010. Campbell Biology. 9th Edition Benjamin Cummings; 9th Ed. (October 7, 2010) 13.^ Raven, P., George Johnson, Kenneth Mason, Jonathan Losos, Susan Singer, 2010. Biology. McGraw-Hill 9th Ed. (January 14, 2010) 14.^ McFadden GI (2001). "Primary and secondary endosymbiosis and the origin of plastids". J Phycology 37 (6): 951–9. doi:10.1046/j.1529-8817.2001.01126.x. 15.^ McFadden GI, van Dooren GG (July 2004). "Evolution: red algal genome affirms a common origin of all plastids". Curr. Biol. 14 (13): R514–6. doi:10.1016/j.cub.2004.06.041. PMID 15242632. http://linkinghub.elsevier.com/retrieve/pii/S0960982204004464. 16.^ Gould SB, Waller RF, McFadden GI (2008). "Plastid evolution". Annu Rev Plant Biol 59 (1): 491–517. doi:10.1146/annurev.arplant.59.032607.092915. PMID 18315522. http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.arplant.59.032607.092915?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dncbi.nlm.nih.gov. 17.^ Georgiades K, Raoult D (2011) The rhizome of Reclinomonas americana, Homo sapiens, Pediculus humanus and Saccharomyces cerevisiae mitochondria. Biol Direct 6(1):55 [edit] ReferencesAlberts, Bruce (2002). Molecular biology of the cell. New York: Garland Science. ISBN 0-8153-3218-1. (General textbook) Blanchard JL, Lynch M (July 2000). "Organellar genes: why do they end up in the nucleus?". Trends Genet. 16 (7): 315–20. doi:10.1016/S0168-9525(00)02053-9. PMID 10858662. http://linkinghub.elsevier.com/retrieve/pii/S0168-9525(00)02053-9. (Discusses theories on how mitochondria and chloroplast genes are transferred into the nucleus, and also what steps a gene needs to go through in order to complete this process.) Jarvis P (April 2001). "Intracellular signalling: the chloroplast talks!". Curr. Biol. 11 (8): R307–10. doi:10.1016/S0960-9822(01)00171-3. PMID 11369220. http://linkinghub.elsevier.com/retrieve/pii/S0960-9822(01)00171-3. (Recounts evidence that chloroplast-encoded proteins affect transcription of nuclear genes, as opposed to the more well-documented cases of nuclear-encoded proteins that affect mitochondria or chloroplasts.) Brinkman FS, Blanchard JL, Cherkasov A, et al. (August 2002). "Evidence that plant-like genes in Chlamydia species reflect an ancestral relationship between Chlamydiaceae, cyanobacteria, and the chloroplast". Genome Res. 12 (8): 1159–67. doi:10.1101/gr.341802. PMC 186644. PMID 12176923. http://www.genome.org/cgi/content/full/12/8/1159. Okamoto N, Inouye I (October 2005). "A secondary symbiosis in progress?". Science 310 (5746): 287. doi:10.1126/science.1116125. PMID 16224014. http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=16224014. Cohen WD, Gardner RS (1959). "Viral Theory and Endosymbiosis". http://www.psychoneuroendocrinology.com/symbiosis.pdf. (Discusses theory of origin of eukaryotic cells by incorporating mitochondria and chloroplasts into anaerobic cells with emphasis on 'phage bacterial and putative viral mitochondrial/chloroplast interactions.) http://en.wikipedia.org/wiki/Endosymbiotic_theory

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  傻傻笑 (专注天体生物学的研究) 组长 楼主 2011-11-24 18:16:12

  Hydrogen hypothesis From Wikipedia, the free encyclopedia The hydrogen hypothesis is a model proposed by William F. Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion arose as an endosymbiont within a prokaryote (an archaea), giving rise to a symbiotic association of two cells from which the first eukaryotic cell could have arisen. According to the hydrogen hypothesis: The host that acquired the mitochondrion was a prokaryote, a hydrogen-dependent archaea, possibly similar in physiology to a modern methanogenic archaea which uses hydrogen and carbon dioxide to produce methane; The future mitochondrion was a facultatively anaerobic eubacterium which produced hydrogen and carbon dioxide as byproducts of anaerobic respiration; A symbiotic relationship between the two started, based on the host's hydrogen dependence (anaerobic syntrophy). The hypothesis differs from many alternative views within the endosymbiotic theory framework, which suggest that the first eukaryotic cells evolved a nucleus but lacked mitochondria, the latter arising as a eukaryote engulfed a primitive bacterium that eventually became the mitochondrion. The hypothesis attaches evolutionary significance to hydrogenosomes and provides a rationale for their common ancestry with mitochondria. Hydrogenosomes are anaerobic mitochondria that produce ATP by, as a rule, converting pyruvate into hydrogen, carbon dioxide and acetate. Examples from modern biology are known where methanogens cluster around hydrogenosomes within eukaryotic cells. Most theories within the endosymbiotic theory framework do not address the common ancestry of mitochondria and hydrogenosomes. The hypothesis provides a straightforward explanation for the observation that eukaryotes are genetic chimeras with genes of archaeal and eubacterial ancestry. Furthermore, it would imply that archaea and eukarya split after the modern groups of archaea appeared. Most theories within the endosymbiotic theory framework predict that some eukaryotes never possessed mitochondria. The hydrogen hypothesis predicts that no primitively mitochondrion-lacking eukaryotes ever existed. In the 10 years following the publication of the hydrogen hypothesis, this specific prediction has been tested many times and found to be in agreement with observation. [edit] References López-Garćia P and Moreira D (1999). "Metabolic symbiosis at the origin of eukaryotes". Trends Biochem Sci. 24 (3): 88–93. doi:10.1016/S0968-0004(98)01342-5. PMID 10203753. Martin W and Müller M (1998). "The hydrogen hypothesis for the first eukaryote". Nature 392 (6671): 37–41. doi:10.1038/32096. PMID 9510246. Poole AM and Penny D (2007). "Evaluating hypotheses for the origin of eukaryotes". Bioessays 29 (1): 74–84. doi:10.1002/bies.20516. PMID 17187354. Embley TM and Martin W (2006). "Eukaryotic evolution, changes and challenges". Nature 440 (7084): 623–630. doi:10.1038/nature04546. PMID 16572163. http://en.wikipedia.org/wiki/Hydrogen_hypothesis

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  傻傻笑 (专注天体生物学的研究) 组长 楼主 2011-11-24 20:25:58

  “氢化酶体”与线粒体的关系 作者：佚名 来源：科学时报 2004-12-4 0:40:00

  真核细胞中的线粒体被认为是和细菌一样的内共生体，数百万年前进入细胞系。一些非常原始的单细胞生物（包括几种有重要医学价值的生物，如Ｇｉａｒｄｉａ 和Ｔｒｉｃｈｏｍｏｎａｓ）似乎缺少线粒体，这种“无线粒体”状态被认为代表着来自在生物获得线粒体之前的一个时期的一种遗迹。这一共识受到最新研究结果的挑战。最新研究结果表明，这些生物有细胞器，被称为“氢化酶体”，它们与线粒体有一些相像之处。但关于“氢化酶体”是否在演化上与线粒体类似、或它们是否代表着一种不同的演化品系有很多不同意见。Ｎａｔｕｒｅ 杂志上最近发表的一篇论文（１０月２８号一期Ｎａｔｕｒｅ上的１１０３页）认为，Ｔｒｉｃｈｏｍｏｎａｓ细胞器的生化性质表明，它们与线粒体是不同的。但在本期Ｎａｔｕｒｅ上，研究人员却以类似的数据为依据认为，二者之间关系密切。这一争论还在继续。

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  傻傻笑 (专注天体生物学的研究) 组长 楼主 2011-11-24 20:26:31

  作者：群芳 来源：科学时报 发布时间：2010-4-8 20:49:29 地中海首次发现可终生无氧生活的多细胞动物 在没有氧的环境中生活一向被认为是细菌、病毒和单细胞生物的“专利”，然而科学家日前发现了第一批显然在完全没有氧的环境中生存的多细胞动物。这些神秘的生物栖息在地球上一个最荒芜的环境中：地中海的L’Atalante盆地，这里的盐水密度是如此之大，以至于无法与上层的含氧水层混合。之前在该盆地采集的水样以及沉积物表明，这里存在单细胞生物，然而一项新的研究发现，有一些多细胞动物显然在盐水下的沉积层中生存并繁殖。 意大利和丹麦科学家在地中海海底探寻未知生物时发现，在无氧和高盐度的海底沉积物中，生活着3种属于铠甲动物门（Loricifera）的多细胞动物。它们只有1毫米长，在被发现时保持着活跃的新陈代谢。当它们被采集时，这些动物能够吸收一种经过放射性标记的亮氨酸（一种氨基酸），以及能够标记活体细胞的一个荧光探针——这些证据的存在表明其是活体动物。研究人员同时发现了包含有卵子的生物个体样本——显示出这些动物在无氧环境中具有繁殖能力，以及这些动物蜕皮的证据，研究人员由此而推断，这些小动物在严酷的环境中度过了自己的一生。 这项研究还显示，上述几种生物具有适应无氧环境的生理机制。研究人员发现，这些生物的细胞显然缺乏线粒体，这是一种利用氧为细胞提供能量的细胞器官。取而代之的是，它们似乎含有丰富的氢化酶体，后者是一种能够在无氧或厌氧的环境中完成与线粒体类似工作的细胞器官。这一发现将帮助科学家更好地理解在地球早期海洋中生活的生物到底是什么样子——当时的海洋也几乎没有氧的存在。 研究人员说，以前在海底无氧环境中只发现过多细胞动物的尸体，一般认为它们是沉到海底的，但这次却有证据证明一些多细胞动物可以一直在海底无氧环境中生存。这一发现拓宽了人们对动物生存能力的认识，揭示了自然界中奇特的生物多样性。 研究人员在本周出版的《BMC生物学》杂志上报告了这一研究成果。 （群芳 译自www.science.com，4月8日） 《科学时报》 (2010-4-9 A4 国际) http://news.sciencenet.cn/sbhtmlnews/2010/4/230844.html

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  傻傻笑 (专注天体生物学的研究) 组长 楼主 2011-11-24 20:28:40

  氢化酶体与线粒体的关系 Nature 434 (7374) | doi:10.1038/nature03343 发表日期：05年3月3日

  氢化酶体是厌氧原生生物和真菌中的简单细胞器，它们是双膜的，产生ATP和氢，于是有人提出，它们是线粒体的厌氧衍生物。另一种观点认为，线粒体和氢化酶体起源于同一祖先，即一种兼性厌氧细菌。在纤毛虫Nyctotherus ovalis（生活在蟑螂内脏中）体内发现的一种新型氢化酶体，为氢化酶体起源于一种“善意的”厌氧线粒体的观点提供了新的支持。这一“缺少的环节”（对氢化酶体是独特的，但正像线粒体一样）保持其自己的基因组。它还有需氧生活方式特有的一种电子运输链的残留部分。

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