Would extraterrestrial bacteria be dangerous to us?

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We can survive most earth originated micro organisms because we co-evolved with them. A totally alien microorganism could conceivable wipe out most terrestrial life.

ruveyn

Only if it could somehow target the biology of life on Earth and did so quite virulently. While it might be possible, it would seem to be extremely unlikely.

Suppose the alien organism is not based on DNA or RNA. Our bodily immune system might not even recognize it as a target.

If that were the case, most life on earth would be doomed.

ruveyn

If it never encountered anything like life on Earth before, I suspect that the most likely result, by far, is that it wouldn't post a threat at all. And if it did pose a threat, it would likely be more due to some kind of by-product it might issue rather than as a direct attack.

If it were that alien in biochemistry then how could it be a threat?

It would not have the skills to infect any terrestrial organism.
A microbe has to have specialized skills to be a decent pathogen.

And if it did figure out how to "break and enter" into an earth organism what could it do?

The very fact of its alien biochemistry would mean it would be unable to exploit its host for either sustenence or for reproduction.

The alien microbe would be like a starving man trying to survive by eating nothing but plant fertilizer. Except it would be even worse off than that.

Bacteria causes infection so I would say alien bacteria could do the same regardless of whether it has encountered human life before. Assuming it has dna and can replicate itself then it would pose a threat.

A virus on the other hand may find it harder to cause us problems as it would not have co-evolved with us.

They would not be "bacteria" as such, since that's a specific subset of life on earth, unless they somehow left earth... but microbe-xenos would probably not be able to do much to us unless they happen to come from a planet with environments similar to the inside of a human.

It would only need to be self replicating to cause a threat. If there was nothing on Earth to keep it in check we would be overrun with it.

We have all kinds of self replicating bacteria that pose no threat. Why would an alien bacteria be any different?

Because an alien one could upset the balance that Earth bacteria has evolved to keep. If it could replicate and feed off its surroundings and nothing on Earth could keep it in check then it would be out of control. A little like anti biotic resistant strains.

The keyword in that is "could". It is unlikely that an alien bacteria arriving on Earth would already have evolved to take advantage of some niche.

And not at all like antibiotic resistant strains. Antibiotic resistant bacteria expand to fill a void left by the killing of the non-resistant bacteria by our improper and/or careless use of antibiotics.

There would need to be no niche. A bacterium, or any self replicating cell, would feed off simple proteins and chemicals on Earth. If there was nothing on Earth to stand in its way, to keep its numbers down, it could easily overrun our oceans and land, replacing existing bacteria and so the food chain would be altered at its base. The consequences would be bad for all.

BTW - Have you heard of panspermia?

The reality is that we have an enormous variety of bacteria on Earth and no species of bacteria is able to take over the planet. Your fear that alien bacteria would somehow do what every species of bacteria that we do have has never been able to do is not at all plausible.

I'll worry about it when we actually discover reason that a planet or moon might be harbouring life.

Between the cold vacuum of space, the sterilising radiation of the sun, and the intense heat of reentry i severely doubt even a microbe would survive the ride here anyway.

All of our microbes base their biology on RNA or DNA. This might not be true for an alien microbe.

ruveyn

That's a very good point. There have been suspected fossils of bacteria found in meterorites, but no living bacteria.