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Comment by tlow | Hacker News Reader

This is all very preliminary, a couple of quotes from the article stood out to me:

> Roberts wondered whether bacteria from the gut could have leaked from blood vessels into the brain in the hours between a person’s death and the brain’s removal.

> Roberts acknowledges that her team still needs to rule out contamination. For example, could microbes from the air or from surgical instruments make it into the tissue during brain extraction?

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But you left off supporting evidence from mouse models: "So she looked at healthy mouse brains, which were preserved immediately after the mice were killed. More bacteria. Then she looked at the brains of germ-free mice, which are carefully raised to be devoid of microbial life. They were uniformly clean."

I had no idea we could sustain germ-free life. That's so cool. The obvious evidence that seems to be missing, however, would just be to extract brain tissue from a living animal, no?

that very much contradicts my model of organisms as well.

I thought we ARE 95% germs, DNA wise.

Prokaryotes are thousands of times smaller in mass/volume, so most cells (and maybe even most DNA) can be bacteria while these are nonetheless minor players.

A side note to passing readers: thousands of times smaller in mass or volume means of course only tens of times smaller in diameter, which agrees with the pictures shown in the article and elsewhere.

Yea. The comparison of humans to cockroaches is a useful intuition. Or blue whales to cats.

This is definitely part of it, the estimates claiming 90% bacteria by cell count end up suggesting perhaps a half gallon of actual bacterial volume. As far as DNA, I think the parent stat can't hold for base pairs. Not as a volume issue, but because mammalian genomes are ~3 orders of magnitude larger than bacterial ones. Even at a 10:1 cell count, our base pairs would be 99% human.

Most importantly, though, the 10:1 stat is just outdated. Newer estimates put the number around 1.3:1 instead.

https://journals.plos.org/plosbiology/article?id=10.1371/jou...

This comment was super interesting, thank you.

That does nothing to rule out contamination from a different tissue.

Different methods. Same result. But sure, you can't prove a negative.

How could one possibly rule out contamination by this logic?

By using some procedure that controls for contamination from a different tissue, instead of having no relation to it.

The truth is that it will probably be hard to find conclusive evidence unless we look for this in a living brain.

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