GOLD, A database that keeps track of this, counts more than 3 million prokaryotic genomes (previous post here). Estimates for the total number of bacterial species on Earth go from billions up to a trillion. It seems almost wasteful. Here’s Annie Dillard:
The creator goes off on one wild, specific tangent after another, on millions simultaneously, with an exuberance that would seem to be unwarranted, and with an abandoned energy sprung from an unfathomable font. What is going on here?
Most of these microbes we have no data about. Of a few million (i.e. much less than a percent) we know because we sequenced their genomes, but we have no other information about them. There are around 30,000 species (i.e. a percent of the species we have sequenced) that have been cultured and formally described. Maciej Cegłowski has published a post on how we arrived at this situation on his blog, Mars for the Rest of Us.
A consistent pattern in the new era of discovery has been that some bizarre microbe is discovered living in a preposterous environment like a hydrothermal vent, and then a couple of years later we find out it also makes up 40% of our intestinal flora. For example, Saccharibacteria are ubiquitous in the oral cavity, but the branch of life they belong to was only discovered in 1996 (in a German peat bog), and it took until 2015 to culture the first representative of the phylum, an absolutely tiny fellow who lives on the back of bigger, tougher microbes that like to hang out near the gum line.
Surprises like this were everywhere.
Cegłowski’s conclusion for our ability to find live on Mars or elsewhere:
The biggest lesson of this new era in microbiology is that we’re not very good at finding life. Microbes that have been living not just under our noses, but physically inside our noses, remain unknown to science. The most prevalent organism on Earth, a free-swimming ocean microbe called Pelagibacter ubique, was only identified in 1990, and not successfully cultured until 2002.
Nehaveigur 