Could alien microorganisms "infect" our own microbiome clouds and then "pollinate" us?

Question

I'm trying to make my idea make sense. I wanted to create an parasitic/symbiotic alien species which reproduces/breeds by air or touch, which they are unaware of. They do not understand why their species keep being "born" in other species. They are intelligent and sentient but not highly advanced themselves. They learn everything secondhand as they take over a population. They may learn how to use technology but they don't always learn the inner mechanisms of advanced technology they find on new worlds so often discard technology too advanced for them and use what they can learn to use to further their survival.

Basically they're alien brains that completely replace our own brains after their "infection" reaches our brains, in which their male and female DNA comes together and creates a new growth which then completely consumes our own brains for the nutrients and then grows into their own sentient brains that take over our bodies. Afterwards, the host body sustains them through normal bodily functions and the aliens keep living. Their process of being born is "parasitic", but after they're born, they no longer feed off their host body and then use the bodies as if it is their own, like symbiotic species.

I came up with a way to help make sense of this by using our microbiome clouds, which we all have, which are microorganisms that are on our skin and around our bodies in the air, unseen by our eyes. They're mostly bacteria and viruses but harmless and a part of our bodies' natural ecosystem.

I wanted to further describe the process and see if it makes more sense in how they're infecting others when they invade other worlds. This symbiotic species has evolved to reproduce by spreading their genetic DNA within their own microbiome clouds. This is what I have come up with:

Alien microbiome cloud ecosystem:

Their microbiome is full of microscopic strange microorganisms that feed off the aliens’ microbiome cloud which is full of their DNA. The aliens constantly emit their DNA out into their personal microbiome cloud by sweat or breathing out, which the microorganisms then feeds off of their DNA. However there is so much DNA being emitted by the aliens that these microorganisms often do not eat it all and and so the DNA often sticks to them, much like bees and pollen.

When these aliens come into contact with other species, their microbiome clouds attacks and consumes other species’ microbiome clouds unseen and completely replaces them. In the process, these microorganisms shed the leftover DNA that's sticking to them down onto the other species through the air and onto their skin, which then infects them through their bloodstream when it’s inhaled or absorbed by contact.

It is a type of symbiotic relationship between the aliens and the microorganisms in their microbiome clouds, however the aliens are completely unaware of this process and do not understand why their species keep being “born” in every other species that they come in contact with.

Their microbiome cloud basically infects our own microbiome cloud in order to “infect” us through our bloodstream. Their strange microorganisms are in effect pollinators for the parasitic/symbiotic aliens. These microorganisms are not intelligent, it is just the way they evolved with the aliens on their homeworld and the symbiotic aliens thought their way of existence it was normal until they left their homeworld and started seeing their own species being born and taking over other aliens after first contact. They have no idea that their biology evolved to work in this way.

Does this work??

Answer 1

sort of...

It looks like the goal here is to really lean into the bees & pollen metaphor. Ok, let's see where the problems are and how they might be fixed.

The question tells us that the aliens (technically the host creatures once taken over by the aliens, but aliens is shorter) "constantly emit their DNA". It's not entirely clear what "DNA" means in this context, but it does sound like bare DNA molecules are envisioned. As commenter jdunlop has already noted, that's almost certainly not going to work as DNA is too fragile. So, I'll assume you mean some form of sex cell (i.e., gametes).

Setting aside the immediate squick generated by the idea of constantly sweating out sperm or eggs, there are still some challenges to address.

Gametes, in particular female gametes, are typically fairly expensive cells. Producing them in mass quantities just to feed your local microbiome seems a bit frivolous. But let's not worry about that and just assume the cost is worth it.

Female gametes are also big. The human egg cell, for example, is about 120 microns across. This poses a problem. Bacteria (which I'm using as a generic stand in for the microorganisms in the microbiome) range in size from 0.2 microns to 300 microns with most being 5-10 microns. Going back to the bees & pollen metaphor, this is like bees getting pollen grains the size of an apple stuck to their leg. Obviously, that's not going to work.

So, how can this be fixed? Can the egg be shrunk? Sure, but it's not clear by how much given that it must carry a pretty sophisticated package of DNA and support functions (I'm assuming it needs to be as sophisticated as ours since this is a sapient species). How about shrinking down to 12 microns? I couldn't get 3 dimensional measurements on a human egg so I'm going to assume it's a disk that cannot be made any thinner. So, shrinking to 12 microns means reducing the radius to 1/10 its original size. That means this cell only has 1% of the original's space and is now much smaller than a human sperm cell.

But that's still too big for a microorganism to casually pick up the way a bee picks up pollen. I think this is where the original pollen metaphor breaks.

But maybe all is not lost

Lose the bees and keep the pollen. Plenty of plants just dump their pollen into the air (depending on where you live, maybe you've had to wipe it off the windshield of your car in the morning). What if this creature is pushing out fully formed gametes with some basic bacteria functionality (like being able to enter skin pores, work its way to the brain, etc.)? It's not quite the same but it's kind of close(ish).

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Ok, really what I've come up with is a hybrid of pollination and bacterial infection, but it doesn't seem too far off.

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EDIT

An alternative that keeps the bees

This is getting out there into handvaving territory but hear me out.

There is evidence that some nonmotile microbes will "hitchhike" on motile microbes (paywalled but you can read the highlights). Maybe that's what the gametes here are doing.

The creature's gametes are nonmotile but include an external energy packet that the motile microbes can eat. While the motile microbes eat, the gamete uses their motility to try to get to a viable host. Once they reach a host, the gamete secretes something nasty to chase away the microbe before it gets eaten. Then it goes about its business of stealing a body.

A bit more complicated than the bee & pollen metaphor but it could work (maybe).

Answer 2

The aliens are the microorganisms.

It is simpler. The aliens don't know this. Intelligence (a sort of hive mind) is an emergent property once the microorganisms commandeer the right kind of multicellular life. What the aliens consider to be their own species is just another sentient or semisentient species colonized by these micro-organisms, which are not even native to the alien homeworld. The micro-organisms still exist as micro-organisms outside the bodies of your aliens (and other species that they assimilate)

How exactly the micro-organisms commandeer a macro-organism needs to stay unclear. Having it be DNA based as you lay out risks having people who understand DNA be unable to suspend disbelief or wind up in the weeds of DNA mechanics and disengaged with your story. I think the micro-organisms should move in and the end result creature is a chimera.

Of course this means the alien "people" would be comprised of all sorts of physical forms from the various other worlds that have turned into them. That would be fun to write. They are all from the same culture and consider themselves the same people but if you want to reproduce you will need to find someone whose ancestors were the same species as yours.

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It is all worthwhile because I see this is not just speculative biology for the sake of speculative biology, but you have a vision for your aliens - how they are, what they do, how their civilization works, how they are puzzled by the fact that new civilizations turn into them. I wonder if this is allegorical high science fiction? A commentary on cultural imperialism? I am already engaged in this story! I hope you write it.

Answer 3

It can make sense, in a way.

Our microbiome is untouched by our immune system, so it would represent the ideal backdoor for infiltrating our body.

However our microbiome doesn't extend to the brain, so this organism should start from our skin/guts then use the nervous system to go upstream to the brain and start occupying it.

That this process works on every species is kind of improbable.