http://www.nature.com/news/2006/061009/full/061009-10.html Rather riveting stuff! It also leads back to the orginal question of abiogenesis. How simple can an organism be? A bacterium seems rather rudimentary to us, but it is already quite a sophisticated piece of biological machinery. And it seems they can be simplified to the extreme. This leads to speculation of course since we are not doing science here. The original simple independent organism could have been a symbiosis of many parts that used to be operating independently. They were one by one incorporated into a single organism which increased its complexity accordingly. It never needed to do all functions. It could leech off the environment for certain functions, at one point mastering the function by incorporating it into its structure and genetic system.
well smallest genome sure is interesting aspect to look to. On contrast did you ever hear of a self repairing genome? In humans the telomerases get cut everytime the cell replicates...so were doomed...but in extremophiles (extremophilic bacteria) they got some really neat stuff, what they do is copy their dna as much as 30 times and when it gets damaged by radiation say they use the undamaged dna as the code to make cells. So when an organism has a small dna...a simple organism has less chances of survival, cause if its dna gets damaged it is doomed. Thats why humans have got not just the exons for coding but also introns.
Oh and here is the article on the self-repairing extremophiles: http://www.libertypost.org/cgi-bin/readart.cgi?ArtNum=160256 Perhaps we can apply the same to humans... immortality Hint* Hint*
the more parasitic(??) one lifeform is, the less it needs to synthesise products essential for its life. evolution is very keen to lose organisms ability to make stuff by themself if one doesent really need to.
well im part of evolution, and I am an organism, and I quite feel an urge to make stuff by-myself that is to live longer and that means I want to repair my DNA so it never gets short. I dont know how about you?
virus of E-coli Phi-X 174: 5,386 base pairs and 10 genes in its genome. A virus, though not a living organism, can still be classified by genome size. Human mitochondrian has 37 genes. Also, look into bacterium SAR11 and hyperthermophiles - not sure. Also, the U.S. Dept. of energy has a program involved with finding the smallest genome: http://www.er.doe.gov/ 182 is indeed profound for a bacterium.
Spurious: this is a very informative post and I know for sure that one of my profs and a colleague will be interested in this, as well as I am too! If I remember correctly, the USDOE had a project going where they were trying to create an "artificial" bacterium - whatever that means? - with 300 or less genes. Also, this is the first time that I linked over to Sciforum without logging on - deleted all my cookies - and saw your avatar. I'm jealous! It would've been one that I would have loved to have chosen myself. Do you have a dog?
Hepatitis B only has 4 genes? And to think 4 genes has caused so much pain and suffering to so many people worldwide. Wow! Biology is the most fascinating subject!
Yeah. Sure. That's an interesting subject too, but I like Spurious's post because he is relaying info on "How small can a genome get and still run a living organism." Viruses are so close to being a living organism that that's why I thought this would be relevant to the subject of evolution of a living organism. So would horizontal/lateral gene transfer. One hypothesis for the origin of meiosis is that it originated as a DNA repair mechanism and that genetic variation was only an accidental by-product. But this is a little beyond the subject of the thread. At least in terms as to where I was hoping that it might go, i.e., more towards the origins of life from simple cells. On the above hypothesis see: Berstein, H., F.A. Hopf, and R.E. Michod. 1988. "Is meiotic recombination an adaptation for repairing DNA, producing genetic variation, or both?" In "The Evolution of Sex" by R.E. Michod and B.R. Levin, eds.
A query: With this demonstrated down-sizing of bacteria by endosymbiosis, with presumptively some of the gene functions no longer with the bacterium but with the host (by direct transfer of the DNA from the bacterium to the host?), is it possible that viruses originated by such mechanism - i.e. could a virus be the end-result of extreme loss of DNA functions from a simple bacterium?
What are you talking about? "down-sizing of bacterium"? Shouldn't we be considering the evolution of, and the "up-sizing" of bacterium first??? And then the downsizing of only some species? We have viruses with only 3 genes. Also prions. As I said, I hoped that this thread would focus more on small genome size, and thus the origins of life, not the transgressions that may or may not have occurred afterwards. Walter, You are proving yourself to be a real deviant "Off-the-Wall" radical."
Valich: Your 'insight' into my post is actually informative of your state of mind. What I was suggesting is that possibly some viruses have 'evolved' from bacteria by continuous loss of genes and other functions to the host, which were shed to the host over time, along the lines of the symbiotic bacterium Carsonella ruddii, discussed in the first post above. After all, viruses are entirely dependent upon the host cell's genetic mechanisms for their reproduction. What is so "off the wall" about that suggestion? It might be true, after all. Or, do you have a better suggestion for the origin of viruses? Do you believe they are the precursors of the simplest bacteria, and that the simplest bacteria evolved from a primitive virus? That really doesn't make sense, since a virus cannot survive on its own without a host cell, and seem to require a host eukaryote. While my post does not go to the origins of the simplest bacteria, that was not the nature of the thread. Rather, the thread is about the simplest genome that can still be considered 'alive'. Are viruses 'alive', or do they meet the criteria used to establish what is alive? For that matter, does Carsonella ruddii meet that criteria with so few genes, and inability to survive/reproduce without a host? It is much more like a virus in that regard, in that it cannot live on its own, and relies upon the host cell's genetic mechanism for its own 'survival', just as do viruses. So, take that back to your think-tank, and share with your professors, and tell me how what I have suggested in any way deviates from known biology, so that all may see who is the deviant. Your apology would be appreciated.
I know the precurser of a cell as we know them was a protein bubble with a half dozen bases of rna and small protiens, and we've progressed from there.
Excellent hypothesis! I never thought about it that way, but your idea is credible! Unfortunately my profs here don't seem to be as excited as I am about searching into the origins of live. I was just naturally assuming that you have to start with the basic building blocks and work your way up. And I still do think this way. But I do see how a more advanced genome (a simple bacterium) could have lost genes and then reverted back into perhaps a virus, as you suggest. Yes. This is a very good thought. So please forgive my ignorance in the tone of my reply. Still, however, this doesn't solve how life emerged. I just reread a paper I had read last year that seems much more insightful to me now: "The Ring of Life Provides Evidence for a Genome Fusion Origin of Eukaryotes," by Marcia C. Rivera and James A. Lake, Nature, Vol. 431, Sept. 9, 2004. There's no doubt in my mind that there was never such a thing called a Universal Common Ancestor due to the prevalence of horizontal/lateral gene transfers in early genomes. This is how life emerged! The authors argue very convincingly that the eukaryotic nuclear genome was formed by the fussion of a protobacterium (that they call P lambda: X. fastidiosa 9a5c) and a relative of an archael eocyte (E. S. tokodai). The scientific classifications and phylum names are not what is important in this analyses. The fact is that all basic simple genomes - whether you want to call them organisms or not; viruses or life, or a simple "proto-bacterium" - are much more susceptible to the initial horizontal/lateral gene transfer transduction process. So, working backwards from this assumption, where do we go? I don't know. Any input?
Walter: Read http://www.msnbc.msn.com/id/15300192/ "The earthquake was created when a 36-square-mile plate near the west coast of the "Big Island" slipped about one yard at a depth of about 20 miles below the ocean floor." This suggests that there are multiple small plates where the Pacific Plate deviates in angle under the Hawaiian Islands. I think you should post a new thread about this under Earth Sciences.
Apology accepted. I agree, the evidence is quite strong that eukaryotes (and indeed, likely prokaryotes as well) are derived from horizontal gene transfers from multiple prokaryotes. As to the origins of the simplest bacteria, the conditions likely no longer exist in nature, but at one time the earth's oceans were a soup of amino acids and other molecules, and presumptively a simple replicating molecule of RNA would form from a protein bath, templated by those proteins. Eventually, organization of the protein bath into an 'encapsulated' system that admitted amino acids would allow for such RNA to replicate and the 'encapsulated' system to grow larger, eventually 'budding' (binary fission) into duplicate systems. Such would be the first type of life, I would imagine. As to the recent quake in Hawaii, I happened to be in California at the time, so I missed it, though my family got a bit of a thrill. 30 years ago, a 7.2 quake struck several miles below where I live (Honomu area), causing some damage. I wasn't living there then. We usually feel small quakes from the continuous volcanic activity (every year or two), typically in the 3-4 magnitude range. There is some evidence that Mauna Loa is nearing an eruptive phase once again (averages every ten years for the past 150 years; last erupted 20 years ago). Hopefully, it will miss downslope structures. I live on the flanks of Mauna Kea, which is extinct (we hope), or at least hasn't erupted in 20,000 years, with the last eruptions being the cinder-cone type, as well as some magmatic extrusions under the ice-cap that then covered the top (during the height of the ice-ages, when the top was some 130 meters further above sea-level, as well, and thus even colder).
The origin for the abrupt kink in the Pacific Plate that in part created the Hawaiian Island chain has always been under a lot of debate. I think you participated in a long forum that we had going last year on this. If the hot spot were stationary, then I believe we said that the active volcanic margin should be 19° South of where it is today. This suggests to many that the magma plume is not stationary. However this is the first time I heard anything about a separate plate(s) [36-square-mile plate near the west coast of the "Big Island"]. This throws another wrench into the factors. Yes, I have always agreed with a hypothesis explaining the origin of life as you also briefly describe above: Pre-RNA > RNA World > DNA World. The hypothesis for the much later origin of meiosis as originating as an incidental byproduct of a DNA repair mechanism is basically the origin of sex.
