[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 : 322 points
Date : 2024-12-02 18:20 UTC (1 days 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...
| cbsmith wrote:
| Contamination is possible, but it's hard to explain the
| results that way. Definitely needs replication, of course.
|
| I don't see the point of the samples all being from older
| individuals. Even if it exclusively occurs in older
| individuals (unlikely), it would still mean that the blood-
| brain barrier is not 100% effective (which we already know to
| be true).
| 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.
| cbsmith wrote:
| > Evidence is scarce and the article is talking about brains
| with active illnesses.
|
| They compared them to control brains, which also had
| microbes.
|
| > 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.
|
| That would describe a scenario where the blood-brain barrier
| isn't 100% effective, no? If it's not 100% effective (which
| we know to be true), it is also seems unlikely that 100% of
| the things that cross the blood-brain barrier cause something
| that we currently consider a disease. Heck, in healthy
| individuals, latent taxoplasmosis' effects are often so
| minimial I don't think we'd call it a disease (otherwise 30%+
| of the world has the disease).
| 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.
| cbsmith wrote:
| I mean, we know about all kinds of microbes that can be in
| the brains of "unhealthy" people, and we've known that for
| ages (taxoplasmosis and CJD come to mind).
|
| The association in the article isn't a case of "we didn't
| find it in healthy people", but "we found it in _more_ in
| unhealthy people ".
|
| From the article: "It found that, while there was a
| remarkable diversity of species in the control brains, there
| were often overgrowths of certain bugs in Alzheimer's
| brains."
| CatWChainsaw wrote:
| Biology and binary do not play nice.
| _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.
| layer8 wrote:
| My gut tells me that the gut influences behavior.
| 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.
| biofunsf wrote:
| Aren't viruses much harder to detect than bacteria? Viruses are
| generally smaller and are completely inert without a host cell.
| Bacteria, besides be larger, also have their own metabolic
| processes and distinct structures you can do things like grow
| them in a laboratory culture until the colony is much obvious.
|
| Your comment makes it sound like bacteria are harder to detect
| but if we're already identifying viruses, locating bacteria
| seems easier.
|
| (Though some viruses are bigger than the smallest bacteria,
| like Mycoplasma at 200nm, viruses are generally smaller)
| londons_explore wrote:
| Both are hard to detect if there are only hundreds of them
| amongst trillions of human cells.
|
| At that point, 'just look with a good microscope' becomes
| infeasible, and you end up needing biological tricks like DNA
| amplification.
| eleveriven wrote:
| And it makes me wonder how much we're still missing or
| overlooking in the microbial landscape of our own bodies.
| 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.
| forgotoldacc wrote:
| > There's nothing like the blood brain barrier basically
| anywhere else.
|
| There is. The placenta and, oddly, prostate as well.
| __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).
| eru wrote:
| Or get a piercing.
| InDubioProRubio wrote:
| So getting pierced, puts one topological outside of
| baseline humanity?
| __MatrixMan__ wrote:
| I suppose it does. Be careful, you wouldn't want to end
| up homeomorphic to the wrong crowd.
| moi2388 wrote:
| Aren't tattoos injective?
| worksonmymach wrote:
| If I met a 8 holed donut I'd tear it a new one.
| __MatrixMan__ wrote:
| I expect I'd start by tearing it one fewer: now a seven
| holed donut with some stubs.
| 725686 wrote:
| Michael Stevens of VSauce fame has you covered with his
| "How Many Holes Does a Human Have?" video:
|
| https://www.youtube.com/watch?v=egEraZP9yXQ
| tmnvix wrote:
| Thanks for mentioning this. I really enjoyed the video
| and learned a thing or two. Would recommend!
| weberer wrote:
| We already know of harmful pathogens that can infect the
| brain, such as Borreliosis. The only jump now is the fact
| that there could also exist harmless bacteria.
|
| https://pmc.ncbi.nlm.nih.gov/articles/PMC8232152/
| adrian_b wrote:
| Spirochetes are much more efficient than most bacteria at
| moving through very viscous media, which include the
| obstacles encountered when moving through an animal body.
|
| Thus, both the spirochetes causing Lyme disease and those
| causing syphilis have high chances of reaching even the
| brain, while traveling through the body.
|
| Fortunately, for the bacteria employing other means of
| locomotion it is usually more difficult to pass through
| many of the internal body tissues, as long as those are
| intact.
| mschuster91 wrote:
| > But unless they're somehow getting from brain-to-egg-
| to-brain that's hard to explain.
|
| There are pathways from the outside to the brain - most
| notably the nose and the eyes. The former have a known
| pathogen pathway (naegleria fowleri, a virtually 100%
| fatal parasite), the latter are actually an
| immunoprivileged site [1] and investigations are ongoing
| what the role of eyes is in the transmission of H5N1 bird
| flu.
|
| [1] https://www.aao.org/eye-health/tips-prevention/eye-
| immune-pr...
|
| [2] https://www.unmc.edu/healthsecurity/transmission/2024
| /06/04/...
| 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.
| 20after4 wrote:
| > even our own immune system doesn't have access
|
| I thought that was recently found to be false? Or at least it
| isn't the full picture. see for example:
| https://www.science.org/doi/10.1126/science.abo7649
| s1artibartfast wrote:
| It is certainly true as a rule of thumb, although there may
| be more going on locally that was previously thought
| panabee wrote:
| This is unrelated to your main point, more to clarify an edge
| case for those interested in learning more: B cells can
| breach the BBB under certain conditions.
|
| At least one pathogen, Epstein-Barr virus, is known to
| inhabit B cells.
| ghurtado wrote:
| > Having bacteria in the gut is more obvious and makes more
| sense.
|
| It probably has to do with the fact that, topologically
| speaking, the stomach (and the whole GI tract) is technically
| on the outside of our bodies.
| eleveriven wrote:
| But bacteria are incredibly adaptable
| 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.
| tomcam wrote:
| I am skeptical that the brain wouldn't have a microbiome
| throwawaymaths wrote:
| There are regions of the body that almost certainly do not
| have a microbiome, for example the viteous humor
| tomcam wrote:
| I'm talking about the brain in particular. A lot goes on
| and it consumes a ton of resources.
| F-Lexx wrote:
| > A lot goes on and it consumes a ton of resources.
|
| But why should this be taken a sign of a brain
| microbiome? I fail to see the connection you're implying.
| seizethecheese wrote:
| A start: do fish have a blood brain barrier that's similar to
| humans?
| fasteo wrote:
| This is indeed the first question to ask. According to
| ChatGpt (don't beat me up)
|
| >>> Yes, fish brains have a blood-brain barrier (BBB)
| card_zero wrote:
| You can't just say "don't beat me up" and expect not to be
| beaten up.
|
| Anyway there's a pdf here that probably tells what _kind_
| of a BBB zebrafish have.
|
| https://www.mdpi.com/1422-0067/22/22/12111
|
| And the article itself says "... communities of bacteria
| thriving in salmon and trout brains. Many of the microbial
| species have special adaptations that allow them to survive
| in brain tissue, as well as techniques to cross the
| protective blood-brain barrier."
| fasteo wrote:
| ha, I guess you are right
|
| https://en.wikipedia.org/wiki/Self-fulfilling_prophecy
| glfharris wrote:
| CSF sampling is a routine investigation in most hospitals. We
| don't typically see bacteria in these samples, when we do, its
| in the form of bacterial meningitis, hence the skepticism.
| biofunsf wrote:
| When something seems obvious to me but scientists in the field
| disagree, I usually take this a sign I need to improve my own
| understanding.
| lolinder wrote:
| Unfortunately as often as not this doesn't seem to be the
| case. Expertise in a field often seems to create blinders.
| eleveriven wrote:
| And I think the brain, like other organs, might have its own
| microbial community, even if it's a small or specialized one.
| sumitkumar wrote:
| I like to think that the bacteria are only on the outermost
| layer of the body, i.e. skin. It just happens so that the
| respiratory and the digestive systems are the exterior part of
| the body which are inside our body. In other words epithelial
| cells mark the boundary of inside and outside and bacteria are
| usually tolerated on the outside and not inside.
| dr_dshiv wrote:
| So, what does that say about the possibility of fungal
| symbiotes?
| lm28469 wrote:
| > It's interesting to me that it would ever have been
| considered outlandish
|
| Not so long ago we thought fish or even human babies didn't
| feel pain, we take a lot of things for granted.
| https://hms.harvard.edu/news/long-life-early-pain
| 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
| pvaldes wrote:
| But evidence of absence is, and in this case we have a
| lot.
|
| For the last 400 years, pathologists on every country had
| filleted and put, lets say tens thousands of human brains
| and human guts under the microscope. One of them has
| systematically a microbiome, easy to see. The other
| don't, except when is diseased or rotten. The sample
| token here is huge, maybe millions.
|
| If we would had searched 400 years for this chocolate
| teapot without finding it, we could conclude with a solid
| suspicion that there is not such thing.
|
| This is very different than just saying "I don't think
| that there is bacteria in the brain but I never searched
| for it". All pathology science is based in searching for
| it. We created gram staining dyes, scanners, tags, gold
| coated plates for electronic microscopes, DNA analysis...
| exactly for that.
|
| If there really is a microbiome living in each healthy
| brain, we should have found it 150 years ago.
| tsimionescu wrote:
| > For the last 400 years, pathologists on every country
| had filleted and put, lets say tens thousands of human
| brains and human guts under the microscope. One of them
| has systematically a microbiome, easy to see. The other
| don't, except when is diseased or rotten. The sample
| token here is huge, maybe millions.
|
| Is that really the case? By my understanding of the
| article, we find plenty of bacteria whenever we look at
| human brain samples. The problem is that it's very hard
| to tell if that bacteria was already present in the
| brain, or if it got in through the process of cutting the
| brain open (especially by contamination with other
| tissues), or if it was indeed present before the
| procedure, but only because the individual was very old
| or had a disease.
| vlovich123 wrote:
| Yeah exactly. It's not an unreasonable search and we
| don't have confidence our search methods work. Hell, the
| Ryugu sample was contaminated while in a hermetically
| sealed clean room filled with nitrogen gas. Either the
| blood brain barrier is even more effective or maybe the
| story isn't quite so clear. This is not an unreasonable
| hypothesis nor do have we exhausted search. Hell, we're
| literally talking about it in response to a related find
| in another species. So it's definitely not a wild theory
| or one that conflicts with known theories.
|
| The chocolate teapot example is a non sequiter as it
| fails both Occam's razor and the principle that
| extraordinary claims require extraordinary evidence not
| to mention that it wouldn't follow any laws of known
| science and it's existence very well would upend quite a
| few of those. The scientific method isn't something you
| get to apply piecemeal.
| rapjr9 wrote:
| Unfortunately many people claim an absence of evidence
| _without_a_thorough_search_ is evidence of absence. As in
| "I have haven't seen it so it must not exist". Many
| people who are experts do this. There needs to be some
| new terminology here, just saying "there is no evidence"
| is meaningless, people need to start saying "there is no
| evidence after <these> kinds of searches" to qualify
| their statements. Like "I haven't seen any evidence, but
| I haven't really looked", or "I asked some of my
| collegues and none had seen any relevant papers", or "I
| did a PubMed search and found no papers on that topic",
| or "I did a PubMed search and found 10 low quality
| studies that showed no evidence of that". Otherwise it is
| completely reasonable to interpret "there is no evidence"
| as "I don't know".
| 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...
| pazimzadeh wrote:
| Our defenses are also crazy. For example, the inner mucus
| layer of the colon is able to keep trillions of bacteria at
| bay the vast majority of the time (unless there is
| inflammation or takeover by specific mucus-eating
| bacteria). Many of the proteins in the secreted mucus
| layers are still unknown in function, like FCGBP which
| comprises up to 40% of the protein content of mucus.
|
| The inner of the two Muc2 mucin-dependent mucus layers in
| colon is devoid of bacteria
| https://pubmed.ncbi.nlm.nih.gov/18806221/
|
| Bacteria penetrate the normally impenetrable inner colon
| mucus layer in both murine colitis models and patients with
| ulcerative colitis https://gut.bmj.com/content/63/2/281
|
| So I think without trillions of bacteria to exclude, in the
| absence of any other issues excluding bacteria from the
| brain seems pretty doable.
|
| Many viruses infect neurons, but they are way smaller than
| bacteria.
| 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...
| flawn wrote:
| Maybe the first point you make is also the argument for why
| our brain might have a microbiome, as our body is not in
| any way hermetically enclosed, and e.g. amoebas are able to
| infect our brains just by going through our nose.
| codethief wrote:
| From what I understand Joe DeRisi's approach[0] comes
| relatively close to your "blender" idea!
|
| [0]: I already mentioned Adam Savage's excellent podcast with
| him elsewhere in this dicussion but here's a direct link:
| https://m.youtube.com/watch?v=MzzD2F73iGU&t=2s&pp=2AECkAIB
| 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
| ForOldHack wrote:
| I once saw a video about using a scanning tunneling microscope.
| I wanted to get a handle on how hard it was, so I scanned an
| area the size of 4 football fields and found a single dime. It
| takes a long time just to figure out what you are looking for.
| We have literally not even scratched the surface.
|
| I would bet that your search was interesting, and that
| eventually you will find something.
|
| Mikelson-Morely went looking for ether, and Einstein found
| relitivity.
|
| Thank you for your work.
| fragmede wrote:
| > I scanned an area the size of 4 football fields and found a
| single dime.
|
| Despite only finding a single dime, that sounds fascinating.
| Can you say more?
| biofunsf wrote:
| What makes a hypothetical brain microbiome so hard to find? I
| would think that once you're doing microscopy on brain slices
| that a biome would show you quite fast. But if you're still
| optimistic after a negative search I assume there must be many
| reasons why a brain microbiome could exist but still be hard to
| detect.
| 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.
| PartiallyTyped wrote:
| and conversely whether probiotics for the brain might exist.
| singlow wrote:
| Countdown until the nutrition influencers start pushing them.
| AlfredBarnes wrote:
| How much of the thinking/feeling would be due to this
| microbiome? Is this how people develop mental illnesses? Such
| an interesting topic! I hope it gets the funding it needs!
| 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
| eleveriven wrote:
| Just how much we still don't know about the brain and its
| protective systems... It's crazy to think that a major part of
| the brain's anatomy was essentially hiding in plain sight for
| all these years.
| 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
| mr_toad wrote:
| It's rare, but viruses, bacteria, fungi, amoeba, worms and
| other parasites can get into the brain and cause meningitis.
|
| Amoeba can get in via the nose from contaminated water.
|
| https://en.wikipedia.org/wiki/Naegleriasis
|
| You really don't want that happening because they'll literally
| eat your brain.
| 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
| mmmrtl wrote:
| Probably the vast majority of studies are correct and a few
| misinterpret artefacts, and then a journalist uses an evocative
| word like "teeming" without knowing that what they're saying
| doesn't pass the sniff test. Same reason these papers languish
| for years and don't pass peer review in rigorous journals
| nborwankar wrote:
| Not sure if this article provides enough definitive info -
| happened to see it yesterday.
|
| https://www.newscientist.com/article/mg26335104-500-the-brai...
| dukeofdoom wrote:
| Most people will read this headline as a question. I read it like
| a proposition for bio weapon lab research. Post covid.
|
| Parasites can live there. I think, Toxoplasma gondii and malaria
| and a brain eating ameba exists. If you planted a bean in the
| brain of a beagle, it would grow too. Though I hope we don't ever
| do that.
| jexe wrote:
| If this were also true for humans, what would the implications
| be?
| unnouinceput wrote:
| that a bacteria decided to "lemme make this dude ask a question
| on HN". On a serious note, it's already answered in the article
| - it means that our behavior is not only influenced by the gut
| bacteria (already proven), but the brain ones too.
| jexe wrote:
| Well finally I have a new excuse to ask dumb questions
| here...
|
| But what I mean is, what are the downstream consequences of
| this knowledge? Does it change how we can reason about
| health, cognition, etc?
| unnouinceput wrote:
| unknown. they barely suspect this, to your question is
| another leap in science for future generations of
| researchers
| Vaslo wrote:
| What would this say about taking antibiotics? Would the blood-
| brain barrier keep them out?
| unnouinceput wrote:
| no. they are molecules, and they are let in by the barrier.
| biofunsf wrote:
| It depends. Some antibiotics pass the BBB easier than others.
| Some are used especially when passage through the BBB is
| desired.
| piombisallow wrote:
| The whole microbiome thing is way overblown. It's like studying a
| great city by looking at rats in the sewer. And yeah, maybe some
| people have rats in their houses too. That's doesn't really tell
| you much about the city.
| amit9gupta wrote:
| There has been some research on this, establishing the presence
| of microbiome in the brain:
|
| https://www.biorxiv.org/content/10.1101/2023.02.06.527297v1
| mmmrtl wrote:
| Why hasn't it passed peer review yet? Maybe because they only
| used techniques prone to artefacts. IMO if a brain microbiome
| exists in healthy people it would have been seen already, with
| all the microscopy and sequencing done
| eleveriven wrote:
| Sooo our brain might not be sterile (frighteningly). And we might
| see a shift in how we approach even mental health in the future.
| pvaldes wrote:
| > Is possible that the bacteria were swallowed by the white cells
|
| Then this would hardly count as brain "microbiome".
|
| Do wolves have a macrobiome of deer inside wolves guts?.
| skirge wrote:
| left-handed and right-handed bacteria determining political
| beliefs
| leptons wrote:
| That would explain a lot of things that seem completely
| baffling.
| ttyprintk wrote:
| Consider a worm attacking the judgment and inhibition center.
| Pigalowda wrote:
| I'm skeptical but there's plenty of intracellular bacterial
| pathogens. Perhaps there's an intracellular commensal
| bacteria/symbiote.
|
| I think if it was extracellular we would see it more often in CSF
| - which is collected quite a bit in healthcare. Regular
| histology/pathology slices and staining would detect as well.
|
| I could imagine an intracellular commensal bacteria that is small
| and virtually indistinguishable from an organelle like a
| mitochondria or lysosome that may exist.
|
| Mitochondria were already bacteria at one point. Could there be
| another endosymbiont?
|
| Mitochondria have circular DNA and phage like polymerase. Perhaps
| our secret symbiont can be found through DNA studies.
|
| Examples of intracellular bacterial pathogens include: Brucella
| abortus Listeria spp. Chlamydia spp. Rickettsia spp. Ehrlichia
| spp. Anaplasma spp. Coxiella spp. Mycobacterium tuberculosis
| Salmonella spp.
| m0ose wrote:
| Dr Salinas is awesome. She did an interview on "The Children's
| Hours" about lung fish that was so interesting. Her fish research
| is leading to a ton of human immunology understanding.
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