It seems the function is very forceful indeed! I've never heard of a species actually favoring some bases over others because of the incrementally higher metabolic cost:
The spareness of its genome is related to its frugal lifestyle. The shorter the length of DNA that needs to be copied each generation, the less work there is to do.(me to Pelagibacter: "Dude, that is extreme!"Pelagibacter has even gone one step further. It has chosen where possible to use genetic letters - or base pairs - which use less nitrogen in their construction: nitrogen is a difficult nutrient for living things to obtain.
Something occurs to me: In larger populations, natural selection plays a more significant role than in smaller populations. That's why biologists talk about genetic drift being more significant players in speciation, as the small breakaway population gets isolated from the bigger parent population.
So if these "estimated 20 billion billion billion" Pelagibacters are spread out all across the oceans, that's one huuuuuge population. Neutral mutations would have no chance at all to spread across the population, let alone even a minisculely harmful mutation. So any genetic innovation, which might survive in a small founder population long enough to develop into something positive, would never get the chance to start the experiment.
"So if these "estimated 20 billion billion billion" Pelagibacters are spread out all across the oceans, that's one huuuuuge population. Neutral mutations would have no chance at all to spread across the population, let alone even a minisculely harmful mutation. So any genetic innovation, which might survive in a small founder population long enough to develop into something positive, would never get the chance to start the experiment."
IOW it's setting itself up for extinction?