Humanity is rapidly learning the importance of the microbiome – all the invisible lifeforms that live in and on the human body. And the microbiome is now part of each person’s genome (RNA/DNA that makes you, you!).

Your genome is the sum total of every smidgeon of RNA and DNA in and on your body.

All-together our unique microbiomes help define the theater of activity in which we think, feel, and live our lives. Beyond our visible bodies all of our invisible, personal microbes are now included in our personages that everyone knows and loves. (BTW: Love the hat the Akkermansia muciniphila is sporting today.)

For thousands of years, people thought of a human being as the body, mind, and spirit. Now it’s body, mind, spirit, plus the living organisms: bacteria, archaea, spirochetes, fungi, mycoplasma, protozoa, and others. But wait, there’s more.

What about virus, viroids, plasmids, prions, phages, and free DNA that also hitch a ride through life in-and-on a human body? After all, bacteria are hosts to viruses living inside it. And the other questionable organisms impact the human being (for better or worse) via metabolic molecules, nucleic acids, lipids, polysaccharides, and proteins. Are they “alive” or just “free roaming particles”?

While astronomers debate if the beloved runt-orb, Pluto, is allowed in the planetary club, or relegated to the children’s table of dwarf planets where Eris has to sit; biologists must decide what constitutes the human microbiome? (Pluto got demoted. The microbiome expanded.)

Formerly, Science was not sure if a virus was “alive” according to a preexisting definition of “alive.” Here’s the old checklist of what proved something is alive. (See if you qualify):

  • Made of cells
  • Mobility
  • Uses energy
  • Responds to stimuli
  • Grows, develops
  • Reproduces
  • Adapts to environment

But as of 2020, Science expanded the definition of the human microbiome1 (and is still debating if a virus is alive or not quite. Just a matter of definition.

The consensus is to be inclusive. Viruses, prions, viroids, plasmids, phages, are all in the “alive enough to be part of the human microbiome” category. Note: crystals, although they grow and adapts to the environment, do not yet make the cut.

Even though a coronavirus can’t stand on its own 74 surface spikes, and requires a host for replication, if it’s in-or-on the body, then it counts as part of the microbiome.

Next time you say, “Howdy!” to someone, you are addressing the trillions and trillions of living microorganisms that inhabit the theater of activity – aka the body. You are also addressing the trillions of organized, gift-wrapped nucleic acids and enzymes, aka viruses plus other miniscule particles.

It’s tough matching items to a pre-conceived definition when in life, everything changes, everything matters.


  1. Berg G, Rybakova D, Fischer D, et al. Microbiome definition re-visited: old concepts and new challenges [published correction appears in Microbiome. 2020 Aug 20;8(1):119]. Microbiome. 2020;8(1):103. Published 2020 Jun 30. doi:10.1186/s40168-020-00875-0