Unser Haushund: Eine Spitzmaus im Wolfspelz? - Wolf-Ekkehard ...

165that confer and increase the ability to transport citrate in an atmosphere containing oxygen. They divide themutations conceptually into three categories: 1) potentiation; 2) actualization; and 3) refinement. "Actualization"is the name they give to the mutation that first confers a weak ability to transport citrate into the laboratory E.coli. (It turns out that the bacterium is lacking only a protein to transport citrate into the cell in the presence ofoxygen; all other enzymes needed to further metabolize citrate are already present.) The gene for the citratetransporter, citT, that works in the absence of oxygen is directly upstream from the genes for two other proteinsthat have promoters that are active in the presence of oxygen. A duplication of a segment of this regionserendipitously placed the citT gene next to one of these promoters, so the citT gene could then beexpressed in the presence of oxygen. Gene duplication is a type of mutation that is known to be fairly common,so this result, although requiring a great deal of careful research to pin down, is unsurprising.Over time the mutant got better at utilizing citrate, which the authors called "refinement." Further workshowed this was due to multiple duplications of the mutant gene region, up to 3-9 copies. Again, geneduplication is a fairly common process, so again it is unsurprising. In another experiment Lenski and coworkersshowed that increasing the concentration of the citrate transporter gene was sufficient in itself toaccount for the greater ability of E. coli to grow on citrate. No other mutations were needed.A more mysterious part of the whole process is what the group called "potentiation." It turns out that theoriginal E. coli they began with decades ago could not benefit from the gene duplication that broughttogether a citT gene with an oxygen-tolerant promoter. Before it could benefit, a preliminary mutationhad to occur in the bacterium somewhere other than the region containing the citrate-metabolismgenes. Exactly what that mutation was, Lenski and coworkers were not able to determine. However, theyexamined the bacterium for mutations that may contribute to potentiation, and speculated that "A mutationin arcB, which encodes a histidine kinase, is noteworthy because disabling that gene upregulates thetricarboxylic acid cycle." (They tried, but were unable to test this hypothesis.) In other words, the"potentiation" may involve degradation of an unrelated gene.D. h. auch in den Untersuchungen des Lenski-Labors mit Billionen von Bakterienüber mehr als 50.000 Generationen konnten keine (durch Zufallsmutationenentstandenen) neuen funktionalen DNA-Sequenzen (Gene) für die Bildung völligneuer Proteine nachgewiesen werden – wie viel geringer ist dann erst dieAussicht, dass sich durch diesen Mechanimus völlig neue Gene im Zuge derKurzzeit-Domestikation des Grauen Wolfs gebildet hätten!Abschließend stellt Behe in seinem Beitrag fest:"In my own view, in retrospect, the most surprising aspect of the oxygen-tolerant citT mutation was that itproved so difficult to achieve. If, before Lenski's work was done, someone had sketched for me a cartoon ofthe original duplication that produced the metabolic change, I would have assumed that would be sufficient-- that a single step could achieve it. The fact that it was considerably more difficult than that goes toshow that even skeptics like myself overestimate the power of the Darwinian mechanism."Aber immerhin: Durch diese Genduplikationen ist eine metabolische Veränderung(metabolic change) für ein neues environment induziert worden 290 . Das zeigt, dasseine Anpassung an veränderte Umweltbedingungen durch diesen (Zufalls-)Mechanismus möglich zu sein scheint (siehe Einschränkung in der Fußnote) – wennauch erst durch den Einsatz gewaltiger Zahlen von Individuen und Generationen 291 ,die bei Säugetieren sowie bei der Domestikation des Grauen Wolfs [“a few wolves gaveup their freedom in exchange for our garbage”] in wenigen tausend Jahren gar nichtgegeben sind und damit für diese entfällt.Unter der bisher unbewiesenen Voraussetzung, dass vielleicht einige wenigeCNVs mit Genduplikationen beim Hund (und zwar CNVs, die beim Grauen Wolf290 - Eine Umwelt zwar, die – soweit ich das bisher verstehen kann –, so in der Natur so überhaupt nicht existiert und durch einen Prozessüber mehrere Stufen, der ohne die ganz gezielt eingesetzte menschliche Hilfe nie zustande gekommen wäre. Mit anderen Worten: So theyprepared E. coli for a totally artificial environment in which the bacteria will never occur and - even if these surroundings existed in the wild -would never survive inasmuch as several steps with billions of bacteria over thousands of generation would be necessary to cope with that strangehabitat/milieu which would consist of extraordinary amounts of citrate and oxygen. (Auf die Frage "Is their any natural environment where theability to transport citrate in an atmosphere containing oxygen would be useful for E. coli?” Antwortete mir Michael J. Behe am 20. 11. 2012: "Ifthere is such an environment, I haven't heard of it and Lenski hasn't mentioned it. He has taken pains in his papers to say that the inability to usecitrate in the presence of oxygen is a species-defining trait for E. coli.”)291 Insbesondere auch die Zahl der Generationen extrapoliert für die letzten 3 Milliarden Jahre.