I was with you until the end, tc, but I don’t see how the need for nourishment, the ability to grow, and the ability (though not the need) to have plasmidic “sex” are necessary preconditions for agelessness. As I stated in the OP, my question of immortality presupposed that unicelled creatures can be killed by disease, environmental deprivation, and Lysol. I even asked what is the correct term for something that can be killed, but will not otherwise die. My question was to unicellular creatures live forever through asexual reproduction unless killed.
The discussion of plasmids does bring up an interesting point - are we being too narrow by defining identity by DNA. After all, plasmids are not truly sexual reproduction - bacteria simply swap portions of their DNA, which is then incorporated into each bacterium’s original DNA. I don’t think anyone claims that the bacterium is a “new” creature after receiving this new DNA. Since a lot of the arguments that the asexually reproduced bacterium are new creatures is based on the semiconservative nature of the DNA, does the plasmid argument change any minds about the definitions of “new” versus “old” bacterium?
What do the last two paragraphs of your quote have to do with this discussion, tc?
There’s nothing in that quote that really disputes the idea that bacteria are essentially immortal.
What do you mean “this step”? Having sex? But bacterial sex (known as conjugation) isn’t necessary. There are other ways bacteria can exchange DNA (trandsuction and transformation) and these exchanges can increase the fitness of the bacteria by making them resistant to antibiotics, for example. But AFAIK none of these methods are required for replication or for survival.
Bacteia don’t have a limit to their replication like eukaryotes do. They can be killed, but they don’t have an inherent aging factor. If you want evidence, read the journals referneced at the link I provided in my second post. That site also says:
Bacteria being able to have “sex” shouldn’t add any confusion here, because there are plenty of bacterial species that aren’t able to have sex. It’s not a universal thing.
SuaSponte, I think if anything, swapping plasmids around reinforces my point about how quickly an “original” cell would disappear. Swapping a plasmid is merely another way to change a cell, making it that much harder for a cell to hang around in its original form.
Did anyone ever find out if an amoebic chromosome is linear or circular? I know tcburnett’s quote said “eukaryote DNA is organized into linear pieces”, but that’s a rather sweeping statement, and I’d like to see something that addresses amoebas directly.