Unknown commensal viruses and microbes?

[Buckaroo Banzai]

I was wondering. Actively harming the host is usually not very good for the parasite, virulence means decreased fitness as well, the fitness of the host sets a sort of margin to the fitness of the organism inhabiting it. That's basically why some viruses have initial high virulence which tends to decrease, as the more virulent strains die off with their hosts, and the less harmful strains let the hosts live long enough.

I've also read that much of the harm done by the virus is actually our immune reaction acting way too much dramatically when it was not needed at all, perhaps because without all the technology and hygiene we humans used to have their immune systems heavily occupied with multiple serious menaces, and now we usually have it idle, and when something appears, it overreacts. Akin to having the US army and no war at all, and using jet-fighters to bomb some wallet thief.

With that in mind, seems reasonable to think, from a layman's perspective, that could be a plethora of unknown commensal viruses and bacterias that are just innocuous, somewhat like "exogenous junk DNA", which is not junk in the sense of non-coding, but for the host's perspective.

And that would be a lot of them... anyone has read about something in this sense?

The closest thing I've seen was this:

Is There Normal Blood Flora?

And references, suggesting the same thing, a healthy normal flora.

I can imagine a few possible hypotheses to why it would not be the case, but I can also come up with counter hypotheses....

So, anyone knows about more real estimates, based on empiricism and serious math, of how much of harmless microbial commensalism could be around us?

 

[CharonZ]

Commensalism only applies to bacteria (or other organisms) as viruses do not have a metabolism.
That being said, there is actually already plethora on information about commensalistic microbes (in fact knowledge about commensalistic gut bacteria sparked the hype with prebiotic foodstuffs) .
In general, the vast majority of bacteria and fungi colonizing animals are commensals. Your gut, skin and so on are heavily covered with bacteria that usually do not harm you. In fact, they have a beneficial effect because due to their presence pathogenic bacteria have a harder time to settle in. Of course many of these commensalistic bacteria can turn into pathogens under certain conditions (e.g. during failure of immune system, acquisition of pathogenicity factors etc.).

Many of the predominant bacteria have are known already (mostly by 16s classification), though efforts are put into getting more precise views of the bacteria by metagenomic approaches.

 

[Buckaroo Banzai]

I thought that most of the known bacteria, such as intestinal "flora", were considered symbiotic rather than commensal, as they' perform useful, perhaps essential, tasks.

I didn't know that a viruses had not the same terms for ecological relationships due to lack of their own metabolism... they're usually spoken of as parasites.

I also didn't know of this whole thing of "metagenomics", it is interesting.

 

[CharonZ]

Unfortunately symbiosis (and related terms) are often used in different ways, depending on context. Quite often the definitions are not really clear.
In most scientific contexts a symbiosis simply refers to an usually intimate association of different organisms. Commensalism is just a special form of symbiosis in which generally no direct metabolic interaction is happening.