[HN Gopher] Fish have a brain microbiome - could humans have one...
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Fish have a brain microbiome - could humans have one too?
Author : rbanffy
Score : 138 points
Date : 2024-12-02 18:20 UTC (4 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| cbsmith wrote:
| Short answer: yes.
|
| https://www.theguardian.com/lifeandstyle/2024/dec/01/the-bra...
| ch4s3 wrote:
| Let's not jump to conclusions. That guardian article is about a
| pre-print study that used frozen brain samples from a single
| tissue bank, and RNA sequencing was done on a single machine.
|
| There's a lot of controversy around this[1], because
| contamination is possible and it's known that the blood brain
| barrier weakens with age. The sample are all from older
| individuals.
|
| [1] https://www.news-medical.net/health/Is-there-a-brain-
| microbi...
| outworlder wrote:
| That doesn't seem to be that clear cut.
|
| Evidence is scarce and the article is talking about brains with
| active illnesses. It could be that there isn't any microbiome
| normally but if the safety mechanisms fail and bacteria
| colonize the brain, that would cause the illnesses described.
| Aloisius wrote:
| From the article:
|
| _> When microbes have been found in the human brain, they are
| associated with active infections or typically linked to a
| breakdown in the barrier due to diseases such as Alzheimer's._
|
| I think the question is whether there is a brain microbiome in
| _healthy_ people, which seems to still be an open question.
| _tom_ wrote:
| Wow. If true, that would be fascinating.
|
| We know that non-brain microbiomes can influence behavior. What
| might something in brain tissue itself do?
| debacle wrote:
| Influence behavior.
| ertgbnm wrote:
| Somehow the brain microbiome is only able to influence the
| gut.
| krackers wrote:
| You can look at toxoplasmosis as an example, synthesizes
| dopamine and is somehow able to selectively modulate
| attraction to predators.
| londons_explore wrote:
| Pretty sure all parts of our bodies are riddled with viruses and
| fungi, and maybe bacteria too if we look hard enough.
|
| They'll just be in low concentrations so they're hard to detect.
| devops99 wrote:
| Look up "Cosmic Death Fungus", there is some (but only some..)
| truth there.
| XorNot wrote:
| That rather speaks against it being a microbiome - it could
| just be incidental contamination the body is in the process of
| cleaning up. To be a microbiome I would expect to a diverse,
| well-adapted quorum of species that find some type of
| symbioses.
|
| Absent that evidence, well biology is probability - something
| is always happening somewhere just by chance and statistics,
| but it doesn't make it a feature.
| devops99 wrote:
| Some do and it has a huge impact on human behavior.
| https://en.wikipedia.org/wiki/Toxoplasmosis
| velcrovan wrote:
| In case it helps others: to find out what the above comment's
| "huge impact on human behavior" is supposed to refer to, you'll
| need to dig into references/footnotes #23, #25, #27, #28 and
| #29 on the linked Wikipedia entry.
| lolinder wrote:
| > Matthew Olm (opens a new tab), a physiologist who studies the
| human microbiome at the University of Colorado, Boulder and was
| not involved with the study, is "inherently skeptical" of the
| idea that populations of microbes could live in the brain, he
| said. But he found the new research convincing. "This is concrete
| evidence that brain microbiomes do exist in vertebrates," he
| said. "And so the idea that humans have a brain microbiome is not
| outlandish."
|
| It's interesting to me that it would ever have been considered
| outlandish. In light of everything we now know about microbiomes
| and microbiology in general, it seems to me as a layman that the
| more radical proposition would be that the blood-brain barrier
| would be 100% effective at keeping out all bacteria, rather than
| the proposition that it probably isn't but that the bacteria it
| does let in tend to be symbiotic.
| outworlder wrote:
| > it seems to me as a layman that the more radical proposition
| would be that the blood-brain barrier would be 100% effective
| at keeping out all bacteria,
|
| Bacteria is not usually found in most organs in the body
| though. Even more so in an organ as important as the brain that
| even our own immune system doesn't have access. The brain has
| its own cells to do that job. In order for bacteria to cross
| the blood brain barrier you need bacteria in the blood first,
| where they aren't normally found without getting under fire.
|
| Having bacteria in the gut is more obvious and makes more
| sense.
| lolinder wrote:
| The lungs, mammary glands, uterus, ovaries, vagina, placenta,
| semen, eyes, skin, and nasal cavity all have their own
| documented microbiome so far, and we've been finding out
| about new microbiomes about once a year. They are not a thing
| that is reserved for the digestive tract.
| outworlder wrote:
| The brain is _unusually_ protected though. There's nothing
| like the blood brain barrier basically anywhere else. Most
| the the tissues you mentioned are exposed to the
| environment in some way. There aren't many ways to reach
| the brain without getting inside the body first(sensory
| organs being the obvious pathway, but even that is a
| stretch).
|
| Not saying it's impossible, just that the skepticism is
| warranted.
| __MatrixMan__ wrote:
| If you were to simplify the human body to a sphere (or
| torus... or whatever corresponds with the number of
| orifices that a human has), then all of the microbiomes
| you've listed would be on the exterior. The brain (and
| heart and kidneys and liver and bones and...) would not be.
|
| The microflora would need to have gotten there somehow,
| something analogous to endosymbiosis. But unless they're
| somehow getting from brain-to-egg-to-brain that's hard to
| explain. As for the others, they're easier, all being along
| the surfaces. Even the gut is on the "outside" in that
| membranes need not be crossed in order to access it.
|
| Although counterpoint: the same argument would apply to a
| fish so I guess it's not impossible. Just more surprising.
| Wilsoniumite wrote:
| I think it depends a bit on how you count but I've heard
| it is an 8 holed donut
| __MatrixMan__ wrote:
| It also differs between individuals (e.g. one can develop
| a fistula).
| BurningFrog wrote:
| Those are all organs that are directly exposed to outside
| materials.
|
| For the more internal organs, bacteria would have to travel
| across a skin of digestive tract barrier.
|
| Unless they're present in the womb as the fetus starts
| growing, I guess.
| askvictor wrote:
| Indeed, those organs expose to the outside world have
| reason to cultivate friendly bacteria for no other reason
| than to take up space, to stop hostile bacteria having a
| place to take hold.
| __MatrixMan__ wrote:
| Agreed. Additionally, one of the mechanisms keeping the gut
| bacteria from taking over the rest of the body is an oxygen
| gradient: anaerobic bacteria in the gut are unlikely to be
| interested in an exploration of the aerobic environment of
| the body. Oxygen diffuses freely across the blood brain
| barrier, so it would not serve as an analogous containment
| mechanism.
| njtransit wrote:
| Is it the blood brain barrier that keeps out bacteria or your
| immune system? Admittedly I know little about biology, but I
| thought bacteria growing inside your body was generally
| considered a "bad thing" (topologically speaking, your
| digestive system is outside your body).
| outworlder wrote:
| Indeed. In order to even try to cross the blood brain
| barrier, an organism would have to be in the blood already.
| If that's unexpected, the immune system certainly won't like
| it. Large compounds and even immune cells aren't supposed to
| cross it. Usually brain infections are from tiny viruses
| because of that, unless they found another way (like ear,
| nose or eye infections, all of them effectively brain
| 'appendages').
|
| Now, it could be the case that in a person with a compromised
| immune system AND a compromised blood brain barrier, that
| organisms would be able to live long enough to reach the
| brain. Once there, they would be mostly shielded from the
| immune system, except for brain glial cells (and I guess
| antibodies; usually the blood brain barrier stops most of
| them)
| dekhn wrote:
| From what I understand about the BBB, it's practically
| impermeable to anything the size of a bacteria (mainly intended
| for gating small molecules like fats and drugs), until an
| individual has some sort of disease or other health problem
| that effects the BBB's integrity. But I can easily imagine that
| some bacteria (harmful, or helpful) could have exactly the
| right surface proteins to indicate it's permitted.
|
| I guess this review/writeup
| https://asm.org/articles/2020/april/how-pathogens-penetrate-...
| covers most of the known mechanisms for traveral of the BBB by
| pathogens.
| j6m8 wrote:
| A few years ago my team mounted what I think was the largest-(to-
| date) scale search for this in electron microscopy brain tissue
| volumes [1].
|
| I STRONGLY believe there is a substantial central nervous system
| microbiome, but (spoiler alert) no evidence found in that search
| :)
|
| If you're excited about this work, the datasets are all freely
| available from BossDB [2] -- well over a dozen petavoxels of it!
| I'd be so curious if models these days could pick up on something
| we missed!
|
| [1]: https://www.biorxiv.org/content/10.1101/2022.07.12.499807v1
| [2]: https://bossdb.org
| outworlder wrote:
| Since I don't have enough information on the topic... how would
| one distinguish a microbiome that was present while the
| organism was alive, from contamination after death?
| j6m8 wrote:
| That's a question more suited to a microbiologist or
| bacteriologist than to me, but my educated guess, at least in
| the electron microscopy case, is that you'll see the bacteria
| inside the depth of the slices, rather than sitting "atop"
| the slices. i.e., if you cut open an apple and find half a
| worm, the worm was in the apple. If you cut open an apple and
| then see a worm on top of the slice, it's possible it arrived
| post-cut.
| lovich wrote:
| > I STRONGLY believe there is a substantial central nervous
| system microbiome, but (spoiler alert) no evidence found in
| that search :)
|
| What gave you reason to believe this if you found no evidence
| of it in your own search?
| attemptone wrote:
| This might be too nitpicky, but isn't believe exactly what
| one has in absence of evidence?
| SamBam wrote:
| They're is no evidence that Russell's Teapot is floating
| out in space in orbit around the sun, AND I don't believe
| that it's there.
|
| If I said "I STRONGLY believe that a teapot is out there,"
| it would be reasonable to ask me why.
| pessimizer wrote:
| Also (and this is a pet peeve of mine), we're talking
| about _evidence_ not _proof_. They 're not the same
| thing. Just because there's evidence that something
| happened, it doesn't mean that it happened.
|
| Evidence is a thing that you _claim_ could be part of an
| valid argument that something happened ( "is consistent
| with"). This isn't a universal definition, but there's
| got to be some separation between proof and evidence.
| When there's evidence admitted into a court case, it
| doesn't necessarily mean that someone is guilty. When
| there's a lot of evidence and still no proof, you can and
| should (and will) still make a probabilistic case that
| something did happen.
|
| So I'd agree with and disagree with you. There's no
| evidence (that you know of) that Russell's Teapot is
| there, which is why you do not believe it is there. If
| somebody does believe it is there, but admits that they
| have no proof that it is there, it would be reasonable to
| ask what _evidence_ makes them believe that it is there.
|
| Where I obviously agree with is that "belief" can't mean
| just something you want to think for no particular
| reason. Or if it does, it's certainly not worth talking
| about.
| vlovich123 wrote:
| Absence of proof is not proof of absence. I would imagine
| that it would take a lot of negative searches by many people
| trying different approaches to rule it out. The searches are
| likely to be carried out by people who believe in the idea
| rather than those that are skeptical they will find something
| (the skeptics will work on reproducing any positive results).
| tsimionescu wrote:
| It should be noted that absence of proof _is_ evidence for
| absence. And since in the physical sciences, unlike
| mathematics, actual proof of absence is impossible, absence
| of evidence (after thorough searches) is the best we 've
| got to form a belief for absence of the phenomenon.
|
| That is, we believe, very strongly, that it's impossible
| for two masses to repel each other gravitationally, for
| example, but we will never have actual proof it's
| impossible.
|
| None of this to say that it's irrational to believe in a
| brain microbiome despite this search seeming fruitless, as
| there are good a priori arguments for expecting one to
| exist.
| KineticLensman wrote:
| > It should be noted that absence of proof is evidence
| for absence.
|
| Exactly. Like the apocryphal small chocolate teapot
| orbiting the Earth
| j6m8 wrote:
| Microbes are CRAZY. They're everywhere. Thermal vent-friendly
| microbes. Space-friendly microbes. Vacuum-resilient, heat-
| resilient, acid-resilient. Microbe-free-environment-friendly
| microbes [1]. It seems hard to imagine that a blood-brain
| barrier could really keep the brain sterile.
|
| We're lucky to live in a scientific era during which a "gut
| microbiome" is taken for granted (heck, even FDA-approved
| treatments depend on it! Google FMT, but don't click "images"
| from your work laptop), but it wasn't so long ago that we
| felt microbes were unlikely to live endogenously and
| harmlessly anywhere in the body.
|
| There were also some hypotheses (untested, if memory serves)
| that COVID-19 influenced olfactory neurons through direct
| infection. Don't tell the blood-brain barrier, but if I were
| a bacterium, the nasal palate would be my ingress strategy.
| Or maybe the gums or gut -- one of the cranial nerves,
| certainly. [edit] I should clarify -- covid is viral, not
| bacterial, but it does show that this is a potential entry
| vector.
|
| The central nervous system is incredibly complicated, and our
| symbiotic relationship with microbes is extraordinary. I
| think it does a disservice to bacteria to suppose they DON'T
| get involved in an organ :)
|
| [1] https://www.space.com/ryugu-asteroid-sample-earth-life-
| colon...
| flir wrote:
| I know nothing about this, so I guess I'm asking "why can't we
| do this?": take some brain, throw it in a blender, and look for
| DNA the same way the ancient environmental DNA people do?
| j6m8 wrote:
| Very hard to clean a blender!
|
| More nitpickfully, one of the big things we care about is if
| the bacteria are living _harmlessly_ in the brain. i.e., site
| of microbes, and a lack of inflammation, will answer more
| than just "are there microbes around".
| dhosek wrote:
| You'd have to get that brain cleanly from the creature to the
| blender.
| bagels wrote:
| You can't find out this way. Removing brains exposes it to an
| outside environment where there are microbes. You can't tell
| if they arrived before or after you removed the material.
|
| Related recent story about earth microbes colonizing what was
| hoped to be a pristine sample of astroid captured in space:
| https://www.space.com/ryugu-asteroid-sample-earth-life-
| colon...
| stenl wrote:
| Cool! Has anything similar been attempted in tumor tissue,
| given the many claims of microbes in tumors? Especially tumors
| not in contact with the exterior.
| mbreese wrote:
| As far as I know, most of the tumor microbiome claims haven't
| held up very well. For example, the 2020 Nature paper
| "Microbiome analyses of blood and tissues suggest cancer
| diagnostic approach" was retracted this past year [1].
|
| Given the ease of contamination of tissues (and databases), I
| tend to be pretty skeptical of tumor microbiome claims --
| especially the wide-ranging claims of microbes being present
| in all tumors.
|
| [1] https://www.nature.com/articles/s41586-024-07656-x
| vasan wrote:
| Gut microbes affect brain too
| andai wrote:
| I recall reading about this 1 or 2 years ago! But I don't
| remember details. Has there perhaps been tentative evidence?
| b800h wrote:
| If this were to be the case in humans, I wonder what effect
| antibiotics would be having on behaviour.
| sethammons wrote:
| I was very surprised that just last year, 2023, we discovered a
| whole ass thin membrane covering the brain we didn't know was
| there.
|
| The thin membrane discovered, again, just last year, is called
| the Subarachnoid Lymphatic-like Membrane (SLYM), and apparently
| acts as a protective barrier separating "clean" and "dirty"
| cerebrospinal fluid among potentially other things.
|
| We don't know a lot.
| hirenj wrote:
| On this topic, you might be interested in this article and the
| related discussion regarding novel anatomy.
|
| https://news.ycombinator.com/item?id=41517059
| AvAn12 wrote:
| Aren't there some kinds of amoeba that can cross the BBB and take
| up residence in the brain? And fungal infections? (Or am I just
| thinking of horror movie plots?)
| lamename wrote:
| The one I know of is terrifying and usually lethal. It gets in
| through the nose/cribriform plate
| https://en.wikipedia.org/wiki/Naegleria_fowleri
| codethief wrote:
| Two months ago we had almost the same topic here on HN and I
| posted a question that no one seemed to be able to answer:
|
| > I mentioned Adam Savage's "Scariest [Podcast] Episode Yet" in a
| different context the other day[0] in which I remember Joe
| DeRisi[1] saying something along the lines of brain & spinal
| fluid being "absolutely pristine" when it comes to the
| presence/absence of a microbiome (in healthy individuals) and
| that it'd be real problem if there were one.
|
| > I'm just a layman but can anyone ELI5 how this can be squared
| with the OP, specifically with statements like
|
| > > It turns out our grey matter is teeming with bacteria,
| viruses and fungi
|
| Can anyone explain this?
|
| [0] https://news.ycombinator.com/item?id=41765112
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