Evidence for endosymbiosis

Discussion in 'Creation vs. Evolution' started by Administrator2, Jan 18, 2002.

  1. Administrator2

    Administrator2
    Expand Collapse
    Administrator
    Administrator

    Joined:
    Jun 30, 2000
    Messages:
    1,254
    Likes Received:
    0
    SUMAC
    John Paul, are you looking for evidence that mitochondria and chloroplasts originated as endosymbionts or evidence that endosymbiosis can be observed today? Doesn't matter, here's evidence for both (actually, I didn't include evidence for the origins of chloroplasts...I can if you want, though).

    Andersson SG, Zomorodipour A, Andersson JO, Sicheritz-Ponten T, Alsmark UC, Podowski RM, Naslund AK, Eriksson AS, Winkler HH, Kurland CG. (1998) The genome sequence of Rickettsia prowazekii and the origin of mitochondria. Nature 396:109-10
    We describe here the complete genome sequence (1,111,523 base pairs) of the obligate intracellular parasite Rickettsia prowazekii, the causative agent of epidemic typhus. This genome contains 834 protein-coding genes. The functional profiles of these genes show similarities to those of mitochondrial genes: no genes required for anaerobic glycolysis are found in either R. prowazekii or mitochondrial genomes, but a complete set of genes encoding components of the tricarboxylic acid cycle and the respiratory-chain complex is found in R. prowazekii. In effect, ATP production in Rickettsia is the same as that in mitochondria. Many genes involved in the biosynthesis and regulation of biosynthesis of amino acids and nucleosides in free-living bacteria are absent from R. prowazekii and mitochondria. Such genes seem to have been replaced by homologues in the nuclear (host) genome. The R. prowazekii genome contains the highest proportion of non-coding DNA (24%) detected so far in a microbial genome. Such non-coding sequences may be degraded remnants of 'neutralized' genes that await elimination from the genome. Phylogenetic analyses indicate that R. prowazekii is more closely related to mitochondria than is any other microbe studied so far.

    Emelyanov VV. (2001) Evolutionary relationship of Rickettsiae and mitochondria. FEBS Lett 501:11-8
    Phylogenetic data support an origin of mitochondria from the alpha-proteobacterial order Rickettsiales. This high-rank taxon comprises exceptionally obligate intracellular endosymbionts of eukaryotic cells, and includes family Rickettsiaceae and a group of microorganisms termed Rickettsia-like endosymbionts (RLEs). Most detailed phylogenetic analyses of small subunit rRNA and chaperonin 60 sequences consistently show the RLEs to have emerged before Rickettsiaceae and mitochondria sister clades. These data suggest that the origin of mitochondria and Rickettsiae has been preceded by the long-term mutualistic relationship of an intracellular bacterium with a pro-eukaryote, in which an invader has lost many dispensable genes, yet evolved carrier proteins to exchange respiration-derived ATP for host metabolites as envisaged in classic endosymbiont theory.

    Emelyanov VV. (2001) Rickettsiaceae, rickettsia-like endosymbionts, and the origin of mitochondria. Biosci Rep 21: 1-17
    Accumulating evolutionary data point to a monophyletic origin of mitochondria from the order Rickettsiales.
    This large group of obligate intracellular alpha-Proteobacteria includes the family Rickettsiaceae and several rickettsia-like endosymbionts (RLEs). Detailed phylogenetic analysis of small subunit (SSU) rRNA and chaperonin 60 (Cpn60) sequences testify to polyphyly of the Rickettsiales, and consistently indicate a sisterhood of Rickettsiaceae and mitochondria that excludes RLEs. Thus RLEs are considered as the nearest extant relatives of an extinct last common ancestor of mitochondria and rickettsiae. Phylogenetic inferences prompt the following assumptions. (1) Mitochondrial origin has been predisposed by the long-term endosymbiotic relationship between rickettsia-like bacteria and proto-eukaryotes, in which many endosymbiont genes have been lost while some indispensable genes have been transferred to the host genome. (2) The obligate dependence of rickettsiae upon a eukaryotic host rests on the import of proteins encoded by these transferred genes. The nature of a proto-eukaryotic cell still remains elusive. The divergence of Rickettsiaceae and mitochondria based on Cpn60, and the evolutionary history of two aminoacyl-tRNA synthetases favor the hypothesis that it was a chimera created by fusion of an archaebacterium and a eubacterium not long before an endosymbiotic event. These and other, mostly biochemical data suggest that all the mitochondrion-related organelles, i.e., both aerobically and anaerobically respiring mitochondria and hydrogenosomes, have originated from the same RLE, while hydrogenosomal energy metabolism may have a separate origin resulting from a eubacterial fusion partner.


    de Souza W, Motta MC. (1999) Endosymbiosis in protozoa of the Trypanosomatidae family. FEMS Microbiol Lett 173:1-8
    A small number of trypanosomatids present bacterium endosymbionts in the cytoplasm, which divide synchronously with the host cell. Crithidia oncopleti, Crithidia deanei. Crithidia desouzai, Blastocrithidia culicis and Herpetomonas roitmani are the best characterized species. The endosymbiont is surrounded by two membranes separated from each other by an electron-lucent space. The presence of the endosymbiont led to the appearance of morphological changes which include the lack of the paraflagellar rod associated to the axoneme, the morphology of the kinetoplast and the association of the sub-pellicular microtubules with portions of the protozoan plasma membrane. Aposymbiotic strains could be obtained by antibiotic treatment, opening the possibility to make comparative analysis of endosymbiont-containing an endosymbiont-free populations of the same species. It is clear that metabolic cycles are established between the prokaryiont and the host cell. The results obtained show that endosymbiont-containing species of trypanosomatids constitute an excellent model to study basic processes on the endosymbiont-host cell relationship and the origin of new organelles.

    Jeon KW, Jeon MS. (1976) Endosymbiosis in amoebae: recently established endosymbionts have become required cytoplasmic components. J Cell Physiol 89:337-44
    A strain of large, free-living amoeba that became dependent on bacterial endosymbionts which had infected the amoebae initially as intracellular parasites, was studied by micrurgy and electron microscopy. The results show that the infected host cells require the presence of live endosymbionts for their survival. Thus, the nucleus of an infected amoeba can form a viable cell with the cytoplasm of a noninfected amoeba only when live endosymbionts are present. The endosymbiotic bacteria are not digested by the host amoebae and are not themselves used as nutritional supplement. While the host amoebae are dependent specifically on the endosymbionts, the latter can live inside amoebae of different strains, indicating that their dependence on the host cells is not yet strain specific.

    Ahn TI, Jeon KW. (1979) Growth and electron microscopic studies on an experimentally established bacterial endosymbiosis in amoebae. J Cell Physiol 98:49-57
    A strain of nonsymbiotic A. proteus was infected with endosymbiotic bacteria isolated from another strain of amoeba which had become dependent on the symbionts after a few years of spontaneously established symbiosis. In the newly infected amoebae, the bacteria avoided digestion and multiplied at a faster rate than the hosts, reaching the maximum carrying number (about 42,000 per amoeba) in fewer than ten cell generations of the hosts. The experimentally infected amoebae were also examined under the electron microscope, and the development of bacteria-containing vesicles was followed. The results show that the infective bacteria that were initially harmful to host amoebae have become harmless and that they have changed in their mode of multiplication during the course of establishing a stable symbiosis with their hosts.


    JOHN PAUL
    Thanks Sumac.

    Endosymbiosis has been touted as the method that gave rise to eucaryotic organisms. That is the evidence I am looking for. From what I have read the only way to infer that is to assume the ToE is indicative of reality.

    Endosymbiosis and The Origin of Eukaryotes http://www.ultranet.com/~jkimball/BiologyPages/E/Endosymbiosis.html


    MILAN
    Well, the homology between the genome of Rickettsia and the mitochondrial genome is remarkable.
    See for instance: Nature 396, 133 (1998)


    JOHN PAUL
    True, but homology is NOT exclusive to common descent. Homology is also evidence for a Common Creator.

    Homology in Biology- A Problem for Naturalistic Science http://www.trueorigin.org/homology.asp


    MILAN
    I fail to see how this imaginative story of the "common creator" can be proposed with a straight face.


    JOHN PAUL
    I say the same thing about the ToE.


    HRG/ALTER EGO
    True, but homology is NOT exclusive to common descent. Homology is also evidence for a Common Creator.

    No, it is not. A creator could have created homologous or non-homologous structures; he could have constructed the bird wing from completely different bones than the mole leg. Therefore the creator hypothesis predicts nothing. Common descent, OTOH, predicts homologous structures.


    JOHN2001
    The main problem that creationists have is that they have no way of testing the "common Creator" hypothesis.
    There are no rules that predict what the Creator was supposed to, and supposed not to have done.

    In the case of homology at the genetic level, we can say that such homology is strongly consistent with common descent. In the case of homology at the level of macrostructures of organisms, it may be a case of common descent combined with convergent evolution. In the past, this was a problem because biologists could rely only on comparative morphology and possibly comparative biochemistry. Today we have comparative genetics to decide issues of relatedness.

    Indeed, it would be possible to disprove common descent if we could show "separate descent" at some level. Yet, the fact that creationists expend effort in attacking the endosymbiosis hypothesis is that prokaryote-eukaryote-archaea are the only remaining candidates for lines of separate descent of any variety which remain.


    JOHN PAUL
    And how do you test the common descent hypothesis?
    According to Dennett during the Evolution series on PBS- there is no way to predict what would be selected for at any point in time.


    In the case of homology at the genetic level, we can say that such homology is strongly consistent with common descent.

    A Creationists say the same about the Common Creator.


    In the case of homology at the level of macrostructures of organisms, it may be a case of common descent combined with convergent evolution.

    Or it may be the case of a Common Creator's Creation reacting to similar environmental pressures.


    In the past, this was a problem because biologists could rely only on comparative morphology and possibly comparative biochemistry. Today we have comparative genetics to decide issues of relatedness.

    Related how? Common Creator or common descent? What is the deciding factor?


    JOHN2001
    And how do you test the common descent hypothesis?

    The first tests of common descent were through comparative morphology. The fact that we can order all organisms in an order of "relatedness", through taxonomy, is the first general piece of information pointing to common descent.

    When comparative genetics was discovered it became possible to test to see if "relatedness" was merely an illusion, or whether this actually penetrates to the genetic level. Indeed, the latter was discovered.

    In particular, the fact that both functioning and nonfunctioning DNA sequences are shared among organisms that appear morphologically to be related, shows strong consistency with the idea of common descent. Furthermore, in eukaryotes, mitochondria have their own DNA which permits a second set of genetic information to test.

    In short, everytime a gene is sequenced, common descent is tested. So far, there have not been seen lines of "separate descent".


    According to Dennett during the Evolution series on PBS- there is no way to predict what would be selected for at any point in time.

    Irrelevant. We can predict what genetics cannot be produced by common descent. For example, we do not see a large amount of horizontal transfer of genes between species, except that which can be accounted for by viral infections.

    The Creator can do anything you want Him to do in this sort of discussion. This is scientifically ad hoc and theologically blasphemeous.

    Unfortunately John Paul does not seem to realize that the very existence of the common cellular structures present in eukaryotes is _extremely_ powerful evidence of the descent of all eukaryotes from a single common ancestor.

    Lacking any alternate scientific theory, we have no choice to accept common descent as a fact.


    SUMAC
    A review of some of the evidence:

    1. Some intracellular organelles contain their own genomes
    2. The genomes of these intracellular organelles resemble the genomes of bacteria
    3. The bacteria with the most similar genomes to these organelles are obligate intracellular parasites that are occasionally endosymbiotic.
    4. The genes that are missing from endosymbiotic bacterial genomes are a subset of genes that are missing from mitochondrial genomes
    5. All of the necessary steps that would be required to transform an intracellular parasite to a mitochondrion have been observed to occur (i.e. gene transfer, morphological transformation, etc).
    6. There's more, but that's enough for now

    If I have this right, the argument against this being evidence for an endosymbiotic origin of mitochondria is that evolution is presumed to occur. Is that right? The argument isn't really that this isn't evidence. The argument is that the presumptions used to interpret the evidence are flawed.

    Okay, let's run with that. If one were to presume Biblical Special Creation, what would this be evidence for? What would be the significance of these observations and could we learn anything about the Creation by studying them?
     

Share This Page

Loading...